High-Rise Buildings – Munichre_ 2002

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					High-Rise Buildings

High-rise buildings in the course of history   Technology of high-rise buildings   Risk potential   Insurance

M           Münchener Rück
            Munich Re Group
                                                  Page                                                      Page

1         Introduction                               4   Fire fighting                             110
                                                  Organizational measures                   111
                                                  Atriums                                   111
2         High-rise buildings in the course of his-
                                                         4.3       Windstorm                                 111
          tory, technology and the environment      8
                                                         4.4       Earthquakes                               115
2.1       Historical development                     9   4.5       Foundations, settlement and
2.2       Architectural aspects and urban                          subsidence                                119
          development today                         12   4.5.1     Foundations                               119
2.3       Financing models                          14   4.5.2     Settlement and subsidence                 121
2.4       Infrastructural aspects                   17   4.6       Water                                     122
2.5       Economic aspects                          21   4.7       Special structural measures               122
2.6       Social and ecological aspects             21   4.7.1     Conversions                               122
                                                         4.7.2     Rehabilitation                            122
                                                         4.7.3     Demolition                                123
3         Technology of high-rise construction      24
                                                         4.7.4     Disposal                                  126
3.1       Planning                                  25   4.8       Other risks                               126
3.1.1     Planners                                  25   4.8.1     Terrorism                                 126
3.1.2     Regulations and directives                25   4.8.2     Impact                                    127
3.1.3     Technical analyses and special                 4.8.3     Collapse                                  132
          questions                                 26   4.8.4     Wear                                      132
3.1.4     Construction licensing procedure          26   4.9       Loss of profit                            132
3.1.5     Other constraints                         29
3.2       Execution                                 31
                                                         5         Insurance                                 138
3.2.1     Foundations                               31
3.2.2     Supporting structure                      35   5.1       Property insurance                        139   Load-bearing parts                        35   5.1.1     Contractors’ and erection all risks   Special construction methods              42             insurance                                 139   Facade                                    45   5.1.2     Advance loss of profit insurance          141   Roof                                      46   5.1.3     Insurance of contractors’ plant
3.2.3     Interior finishing                        46             and machinery                             142
3.2.4     Service systems                           48   5.1.4     Decennial liability insurance             144   Installations                             48   5.1.5     Insurance of buildings, fire insurance    144   Deliveries, vehicles                      49   5.1.6     Loss of profit insurance                  145   Passenger transport, vertical           Loss of rent                              145
          development                               49   Additional costs                          145   Waste disposal                            50   Contingency planning                      145
3.3       Occupancy                                 51   Prevention of access                      145
3.3.1     Maintenance, administration               51   5.2       Third-party liability insurance           147
3.3.2     Conversions                               53   5.2.1     Insurance of the designer’s risk          147
3.3.3     Rehabilitation                            53   5.2.2     Insurance of the construction risk        147
3.4       High-rise construction in the future      54   5.2.3     Insurance of the operational risk         148
                                                         5.3       Problem of maximum loss                   149
                                                         5.3.1     Construction phase                        149
4         Risk potential                            84
                                                         5.3.2     Decennial liability insurance             149
4.1       Design errors                             85   5.3.3     Operating phase                           149
4.2       Fire                                      86   5.3.4     Accumulation control                      152
4.2.1     Examples of losses during the                  5.4       Underwriting considerations               153
          construction phase                        86   5.4.1     Contractors’ and erection all risks
4.2.2     Fire protection on construction sites     89             insurance                                 153
4.2.3     Examples of losses during the                  5.4.2     Contractors’ plant and machinery          153
          occupancy phase                           99   5.4.3     Decennial liability insurance             153
4.2.4     Fire-protection regulations, loss              5.4.4     Insurance of buildings, fire insurance    153
          prevention                               107   5.5       Reinsurance                               155   Regulations                              107   Structural fire protection               107   Active loss-prevention measures          108   6         Summary and outlook                       156
1 Introduction

Page 5                                                                                                         1 Introduction

High-rise buildings have always triggered major
debates and aroused emotion. That is hardly
surprising, considering that this type of building
radiates more symbolic power than almost any other.

1   Introduction

From their beginning in the middle of the last century        Up until the end of the last century, high-rise buildings
and right up to the present day, high-rise buildings have     were still made of solid brick masonry, which ultimately
always been a dominant landmark in the townscape,             required foundation walls up to 1.8 m thick. When steel
visible from far and wide, like the towers of Antiquity and   frames adapted from steel bridge construction were intro-
the Middle Ages. At the same time, this sky-scraping con-     duced, with their increased strength and lower weight,
struction method has always been an ideal means of dis-       builders and architects were able to soar to greater
playing power and influence in the community. In the light    heights. With this steel skeleton, the net weight of the
of this goal, reasonable economic considerations often        structure was considerably lower than that of a solid
recede into the background during the erection and sub-       masonry building; it thus not only cut the costs of con-
sequent use of these high-rise buildings.                     struction, but also gave wings to the architects’ imagin-
A prestige object for the builder, these edifices not only    ation. By the turn of the century, they were designing build-
have an effect on their immediate neighbours, but also        ings that also looked light and delicate as even at that
influence many areas of urban life in very different ways.    time the skeleton structure permitted a large proportion
These aspects will also be taken up in this publication.      of windows on the outer facade.
In the early years, the builders’ urge to rise to dizzying
heights was limited by unsolved technical problems. In        Since then, the construction of high-rise buildings has
recent years, however, a real competition has developed       continued to change with the requirements imposed by
among the builders of skyscrapers to be world champion        air-conditioning and particularly office communications.
at least for a few months before being outdone by a rival     The high-rise office buildings of the nineties have
with an even higher building. Even seemingly Utopian          little in common with their predecessors. Instead of
projects now stand a good chance of becoming reality.         compact walls and ceilings, we now have a high-tech
This rapid development has only become possible be-           structure made up of largely prefabricated elements which
cause the technical conditions and methods used in con-       are welded and bonded together on site. The building
structing high-rise buildings have improved decisively        comprises a skeleton of steel or reinforced concrete which
and in some cases changed fundamentally in the last few       is rounded off by suspended ceilings and false floors
years.                                                        creating the space required for installations. The originally
1 Introduction                                                                                                           Page 6


load-bearing outer wall has been replaced by a pre-             associated with high-rise buildings and the techniques that
fabricated facade.                                              are applied in order to illuminate possible solutions from
However, this complex method of construction promotes           the point of view of both construction technology and
the spread of fire and fumes, and therefore, in conjunction     insurance.
with the considerable concentration of values involved,
represents an extremely sensitive risk both during con-         Moreover, the more broadly based general information
struction and throughout the service life of the building.      available will make it easier not only to assess the risk of
The major fires which broke out in a number of high-rise        high-rise building projects but also to arrive at a price
office buildings shortly before their completion in the early   for insuring such projects.
nineties show how correct the appraisal of the fire risk in     The definition of a high-rise building differs from one
high-rise buildings is. The losses incurred through these       country to the next. For our purposes, we will proceed
fires are several times higher than the amounts of indem-       on the basis of a minimum height of 30 m and will restrict
nity known to date.                                             ourselves to buildings used for residential or office pur-
This is consequently one of the main reasons why high-          poses.
rise buildings constitute a new dimension of risk for the       Despite the various critical voices raised, the construction
insurance industry, one which has made it necessary to          of high-rise buildings has by no means reached its zenith.
draw up new concepts for underwriting, loss assessment          The problem of high-rise buildings is one which we – as
and PML determination throughout every phase of con-            insurers and reinsurers – will also have to consider in the
struction and subsequent use.                                   future.
We therefore believe that this publication on high-rise         This special publication is also intended, last but not least,
buildings is an appropriate addition to our comprehensive       as a means of passing on to others our experience from
series of special publications, particularly those on under-    the major losses that have occurred in the recent past.
ground railways and bridges.
We are fully aware of the fact that many of the aspects
considered with regard to the construction, use and insur-
ance of high-rise buildings naturally apply in the case of
lower buildings too. Nevertheless, we do not wish to limit
ourselves to aspects which only apply specifically to high-
rise buildings. After a brief historical overview, we will
therefore consider in detail all the risks and problems

                                                                                                          03 MONADNOCK BUILDING
2 High-rise buildings in the course of history, technology and the environment

2.1 Historical development
2.2 Architectural aspects
                                          2.3 Financing models
                                          2.4 Infrastructural aspects
                                                                                 2.5 Economic aspects
                                                                                 2.6 Social and ecological aspects
Page 9                                                            2 High-rise buildings in the course of history, technology and the environment


According to the Bible, the Tower of Babel was to
“reach unto heaven” (Genesis 11).
But when the Lord saw what the people had done, He confused their language and scattered them abroad over the face
of all the earth so that they left off building the city.

2     High-rise buildings in the course of history, technology and the environment

2.1      Historical development                                      edge of the roof was no less than 130 feet (roughly 38 m)
                                                                     above the road surface. Due to its elevator, the upper
What could be a more appropriate point to begin our con-             floors were in greater demand than the lower floors. Fol-
sideration of high-rise buildings than with the Tower of             lowing completion of the “Equitable” building, it was the
Babel and then to trace their historical development over            done thing to reside on one of the “top” floors.
the centuries. However, a distinction must be made                   Burnham and Roof’s Monadnock building, which was
between “high buildings” and “high-rise buildings”: “high            completed in Chicago in 1891, must also be mentioned as
buildings” have only a few floors and not uncommonly                 one of the last witnesses of a whole generation of solid
only one, albeit very high floor. They are crowned by a              masonry high-rise buildings. Sixteen floors of robust brick
high roof and turrets (in the manner typical of medieval             masonry rise skywards in stern, clear lines: an astonishing
and Gothic cathedrals). “High-rise buildings”, on the other          sight to eyes accustomed to the frills and fancies of the
hand, have many, usually identical floors of normal height           late 19th century. Standing on an oblong base measuring
one above the other. Seen in this light, high-rise buildings         59 m 20 m, the building is reminiscent of a thin slice
have their origins in the towers of San Gimignano rather             and not only recalls the industrial brick buildings of the
than in the Tower of Babel or ecclesiastical structures.             late 19th century, but also anticipates the formal simplifi-
The first high-rise office building according to this defin-         cation of the later 1920s.
ition was built in Chicago in 1885: the Home Insurance               The buildings rose higher and higher with the spread of
Building. It still stands on the corner of La Salle and              pioneering construction methods – such as the steel
Adams Street, a witness of its times. It has twelve floors –         skeleton or reliable deep foundation methods – as well
there were originally ten, but two were subsequently                 as the invention and development of the elevator. The
added – and was built in roughly eighteen months. The                highly spectacular skylines of North American cities,
architect W. L. B. Jenney used an uncommon new method                particularly Chicago and New York, originated in the early
for the construction of his building: the weight of the walls        years of the 20th century.
was borne by a framework of cast-iron columns and rolled             Glancing over Manhattan’s stony profile, the silhouettes
I-sections which were bolted together via L-bars and the             dotting the first 12 km of the 22-km-long island bear
entire “skeleton” embedded in the masonry.                           vociferous testimony to this dynamic development:
The early Equitable Life Building in New York, which was             – the World Trade Center, currently the tallest building in
completed in 1872, also contributed towards the develop-                New York, 417 m high,
ment of high-rise buildings, for it was the first tall building      – the legendary Empire State Building, built in 1931,
to have an elevator. Although it only had six floors, the               381 m,
2 High-rise buildings in the course of history,
  technology and the environment


2 High-rise buildings in the course of history, technology and the environment                                                        Page 12

08 HONGKONGBANK                            09 MESSETURM, FRANKFURT AM MAIN

–   the United Nations building erected in 1953, 215 m,                          ing to which the height of a building must not exceed two-
–   the Chrysler Building dated 1930, 320 m,                                     and-a-half times the width of the road running alongside
–   the former Pan Am Building completed in 1963, 246 m,                         the building. The building mass was further limited by the
–   the Rockefeller Center (1931–1940), a complex of                             requirement that the floor space index must not exceed
   19 buildings,                                                                 twelve times the area of the site. Among other things, the
– the Citicorp Center built in 1978, 279 m, and                                  zoning law stipulated that only the first twelve floors of a
– the AT&T Building opened in 1984, a pioneering                                 building were allowed to occupy the full area of the site
   building by the post-modern architect Philip Johnson,                         and that all subsequent floors must then recede in zoned
   with an overall height of 197 m.                                              terraces – a requirement of major aesthetic significance,
It is only recently that attention has also turned to interest-                  for this terraced form still dominates the silhouette of
ing high-rise buildings outside North America: Norman                            American skyscrapers today.
Foster’s Hong Kong and Shanghai Bank, Ieoh Ming Pei’s                            All doubts as to the profitability of high-rise buildings
Bank of China in Hong Kong and the twin tops of the                              were set aside with completion of the Empire State Build-
Petronas Towers in Kuala Lumpur, currently the tallest                           ing, the Chrysler Building and other skyscrapers in the
building in the world at 452 m.                                                  1930s, for they would never have been built if they could
High-rise buildings in Germany are a modern develop-                             not have turned a profit. Although rentals proceeded slow-
ment and are concentrated particularly in Frankfurt am                           ly at first when the Empire State Building was completed
Main: today, Frankfurt is the only German city with a                            in the heart of the recession in the 1930s and it was there-
skyline dominated by skyscrapers. One of the tallest build-                      fore known as the “Empty State Building” for many years,
ings in the city is the Messeturm built in 1991 with a                           it subsequently generated satisfactory revenues once all
height of 259 m, which is not much more than half the                            the premises had been let.
height of the Sears Tower in Chicago, currently the tallest
office and business tower in North America with a total                          Cities in Europe and Asia grew horizontally and it was
height of 443 m.                                                                 only when production and services acquired greater eco-
It was the rapid growth in population that originally pro-                       nomic significance throughout the world and the price of
moted the construction of high-rise buildings. New York                          land rose higher and higher in economic centres after the
once again provides a striking example: land became                              Second World War that they also began to grow vertically.
scarce well over a hundred years ago as more and more                            Modern Hong Kong is a striking case in point: it encom-
European immigrants streamed into the city. From roughly                         passes an area of 1,037 km2 (Victoria, Kowloon and the
half a million in 1850, the city’s population grew to                            New Territories), of which only one-quarter has been de-
1.4 million by 1899.                                                             veloped, but with maximum density and impressive effi-
More and more skyscrapers rose higher and higher on                              ciency. Almost all the new buildings, office towers and
the solid ground in Manhattan, as buildings could only be                        particularly residential towers in the New Territories have
erected with great difficulty on the boggy land to the                           more than thirty floors.
right and left of the Hudson River and East River. In this
way, New York demonstrated what was meant by “urban
densification” despite the considerable doubts originally                        2.2   Architectural aspects and urban development today
voiced by experts in conjunction with this development.
The first area development code to come into force in                            As the historical development of high-rise buildings has
New York was the so-called “zoning law” of 1916, accord-                         already shown, the construction of edifices reaching higher
2 High-rise buildings in the course of history, technology and the environment                                                              Page 14

and higher into the sky was – and to a certain extent                              the appropriate and basically essential symbiosis
still is – an expression of power and strength. This is                            between engineering designer and artist has been aban-
equally true of both ecclesiastical and secular buildings:                         doned.
the power, strength and influence of entire families – i.e.
their standing in society – is mirrored in the erection of                       This critical discourse on the architectural, urban develop-
ever taller buildings culminating in a battle to build. The                      ment and economic background is not basically to cast
towers of San Gimignano are one of the best preserved                            doubt on high-rise buildings as such, but it does illuminate
examples of this development. In many North African cit-                         some of the facets that are central to considering the risk
ies, too, this attitude has moulded the townscape for                            potential inherent in high-rise buildings.
many centuries and will no doubt continue to do so in                            This almost inevitably raises the question why high-rise
the future.                                                                      buildings should have to be built in today’s dimensions.
                                                                                 – One reason is indisputably the need for a “landmark”. In
The names of the builders and architects have only been                            other words, to express economic and corporate power
known since the high Middle Ages around 1000 AD. They                              and domination in impressive visual terms. Nothing has
created new stylistic elements and added their “signature”                         changed in this respect since the very first high-rise
to entire periods. Looking back, this makes it difficult for                       buildings were erected.
us today to decide whether these master craftsmen                                – The steadily rising price of land in prime locations and
shaped the various stylistic developments or whether a                             an increasingly scarce supply have made it essential to
number of master builders only became so well known                                make optimum use of the air space. Prices in excess of
because their work reflected the contemporary fashion                              DM 50,000 per square metre are not uncommon for land
trends most accurately. That still holds true today, the only                      in conurbations and economic centres. Despite their
difference being that tastes change very much more rapid-                          height, however, high-rise buildings still occupy areas of
ly and “degenerate” into short-lived fashions. A building                          truly gigantic proportions: the ratio of height-to-base
that reflects the spirit of the times when it is finished can                      width of the cubes in the 417-m-high World Trade Cen-
appear “old” within only a few years. The brevity of the                           ter, for example, is 6:1.
various stylistic trends is one of the reasons for the in-                       – Connections to the infrastructure are improved by con-
homogeneous appearance of modern towns and cities.                                 centrating so many people in such a small area. The
Since architects must expect that later buildings will have                        World Trade Center alone provides jobs for over 50,000
their own, completely different formal identity, they do not                       people – that is the equivalent of a medium-sized town.
see any reason why they should base their own designs                              All institutions of public life are united under a single
on existing standards, particularly as this would merely                           roof and the distances between them have been min-
cause them to be considered “unimaginative”.                                       imized.
Three points become clear if we take a closer look at mod-
ern trends in high-rise construction:                                            However, high-rise buildings do little to prevent land being
– The dictate of tastes mentioned above is expressive of                         sealed on a large scale. The suburbs of modern American
   the egotism prevalent in modern society with its desire                       cities are a prime example: as far as the eye can see, the
   for status symbols and designer brands. Unfortunately,                        landscape is covered with single-family homes, swimming
   the public not uncommonly bows to this dictate, as                            pools and artificially designed gardens simply to provide
   when town councillors set aside major urban develop-                          sufficient private residential land for all the people work-
   ment considerations and with seeming generosity set                           ing in a high-rise building occupying only a few thousand
   up public areas in the form of lobbies and plazas in                          square metres.
   high-rise buildings.                                                          – Many of the techniques and materials which are also
– The sheer magnitude of the projects forces all planners                           used for “normal” buildings today would never have
   to adopt a scale totally out of proportion to all natural                        been invented and would never have become estab-
   dimensions and particularly to the people concerned                              lished if high-rise construction had not presented a
   when planning their buildings. In the past, urban devel-                         challenge in terms of technical feasibility. Rationalized,
   opment plans were easily drawn up on a scale of 1:100                            automated sequences are beneficial to high-rise build-
   or at most 1:200, a scale which could still be directly                          ings; at no time in the past were such huge buildings
   related to the size of a human being. With today’s high-                         erected in such a short space of time. Short construction
   rise buildings, however, a scale of at least 1:1000 is                           periods also mean shorter financing periods and conse-
   required simply in order to depict the building on paper.                        quently profits which partly compensate for the add-
   This is illustrated by the example of the Sears Tower                            itional costs incurred in the construction and finishing of
   in Chicago: completed in 1974, the Tower measures                                the building.
   443 m in height. Drawn to a scale of 1:2000, a human
   being is represented by a minute dot measuring barely
   0.9 mm.                                                                       2.3   Financing models
– In the past, it was the master builder and architect who
   defined the construction and consequently the appear-                         The construction costs for high-rise buildings often run
   ance of a building; today, on the other hand, technical                       into hundreds of millions of dollars. The owner of the
   developments determine what can and cannot be done;                           building will rarely be willing or able to bear these costs

                                                                                                                  11 HIGH DENSITY: HONG KONG SKYLINE
Page 17                                                         2 High-rise buildings in the course of history, technology and the environment

without outside assistance. On the other hand, however,            The developer usually draws up what is known as a mas-
debt service and exhausted credit lines will then constrict        ter plan for complete districts and then retains (usually
his operative freedom. Alternative financing models are            prominent) architects to design the various components of
therefore frequently sought; the best known models are             the master plan independently of one another. The devel-
briefly outlined below.                                            oper then seeks to find tenants or lessees for the building
                                                                   which at this stage only exists on paper. Construction
LEASING                                                            work begins when tenants or lessees have been found.
Leasing of buildings, particularly high-rise buildings, can        La Défense in the Paris Basin is a typical example of such
to a large extent be compared with rentals. This alternative       a development.
is commonly chosen when a company finds itself in finan-           This suburb was created on the drawing board in the
cial straits and needs cash. Selling the building – often a        1950s. A dilapidated district was demolished and com-
prestige object in a prime location – to a leasing company         pletely redesigned. The traffic systems, such as Metro,
is of two-fold advantage to the company: firstly, it acquires      urban railway, motorway and access roads were moved
the urgently needed capital, and secondly, it can continue         below ground level and covered by a concrete slab 1.2 km
to use the building in return for a monthly leasing fee            long.
which, however, amounts to no more than a fraction of the
purchase price received.                                           Mostly office towers were erected on this slab with open
The composition of corporate assets is changed by such a           squares and green areas in between. The ensemble is
transaction. This can be a disadvantage when new loans             rounded off by the Grande Arche de la Défense designed
are needed, for the building is then no longer shown on            by the Danish architect Johann Otto von Spreckelsen and
the assets side as a property secured by entry in the land         completed in 1989. The Grande Arche is a huge cube
register.                                                          which is open on two sides with 37 office floors and a
                                                                   height of 110 m equal to its ground lengths. All the capital
BOT                                                                invested on the site came from private sources and was
BOT stands for “build, operate and transfer” (there are            controlled by a public-law community of interests.
other variations but these will not be discussed in further
detail here). In the case of this financing model, the owner       In times of sluggish investment activity, however, it is not
of the land places his land at the disposal of a contractor        uncommon to find that only certain parts of the master
who then erects a building on it, such as an office tower.         plan are actually realized. Originally planned as a homoge-
The owner of the land can exert a certain influence on the         neous townscape, the result is then nothing more than an
planning and intended use, but does not share in the con-          unrelated fragment and areas that should have been filled
struction costs. The contractor must organize the project’s        with life appear to be deserted and uninhabited instead. In
financing himself, be it with own funds or with the aid of         the mid-nineties London’s Docklands provided a dramatic
loans (“build”).                                                   example of such a development: the transformation of the
In return, the owner of the land waives all or some of the         West India Docks built between 1802 and 1806 resulted in
income from occupancy of the building for a certain                what was for a while the highest mountain of debt in the
period of time, usually 25 years. During this time, the            world with the high-rise obelisk on Canary Wharf. After
builder must obtain rents that are calculated to cover his         having consumed roughly US$ 3bn, the half-finished pro-
debt service and draw a profit from the invested capital           ject was temporarily abandoned before finally being com-
(“operate”). The builder’s risk with regard to rents and           pleted and let following a variety of financial transactions.
debt interest is often considerable. At the end of the
agreed occupancy period, both the land and the office
tower become the property of the landowner (“transfer”).
                                                                   2.4    Infrastructural aspects
There are differences between these financing models: al-
though the BOT model grants the landowner the right to             The different fates of La Défense and Canary Wharf are
ownership, he is for a long time excluded from occupancy           not (only) due to the extremely different planning periods
of the property. With the leasing model, the high capital          of 30 years (La Défense) and 8 years (Canary Wharf), but
investment required is transferred to the lessor and the           above all to the manner in which the necessary infrastruc-
financing costs are replaced by monthly payments akin              ture for the two projects was tackled.
to rent by the lessee.                                             In the case of La Défense, the entire necessary infrastruc-
                                                                   ture was completed before the construction work actually
DEVELOPER                                                          started: underground railway lines and roads, service
The developer is a new profession born out of the explo-           systems were all planned and built beforehand. As a re-
sive rise in construction costs which has been intensified         sult, a fully functional and above all adequately dimen-
by increasingly large buildings and structures. This was           sioned infrastructure was consequently available when the
triggered by urban renewal programmes and changes in               buildings were taken into service. This made La Défense
tax regulations for large construction projects for which          attractive to investors and tenants alike; the new district
new financing models were developed in the USA in the              soon pulsated with life as an economically sound basis for
sixties and seventies.                                             the entire project.
Page 21                                                          2 High-rise buildings in the course of history, technology and the environment

A jungle of political, economic and investment difficulties         major fire or collapse of the building. Despite (or precisely
must be overcome for such prospective planning because              because of) its size, a high-rise building is an incredibly
the owner of the high-rise complex bears no direct respon-          sensitive and vulnerable system. Even a brief power fail-
sibility for the large majority of these far-reaching infra-        ure can result in operational and economic chaos. The
structural measures. The project’s progress is consequent-          same applies to outside disturbances in the form of strikes
ly controlled by the municipal authorities, as well as by           by public transport corporations or a malfunction in the
supply and operating companies and not by the owner of              underground or urban railway system.
the complex.
The situation of Canary Wharf in London’s Docklands
is exactly the opposite and proves that the La Défense
type of planning is the economically more appropriate               2.6    Social and ecological aspects
approach, despite the associated delay in starting con-
struction work and the longer preliminary financing                 Criticism today focuses particularly on the social and eco-
required.                                                           logical effects of high-rise buildings.
A second City of London was to be created in the heart of           The most commonly voiced reservations with regard to
the Docklands within the shortest possible space of time,           high-rise apartment blocks concern the social aspect. It is
with thousands of square metres of tailor-made office               claimed – and there are probably a number of studies to
space, hotels, shops and apartments for high-income ten-            prove – that cohabitation in high-rise buildings does not
ants. A rail-bound fully automatic cabin railway known as           work as smoothly as in homogeneous, historically grown
the Docklands Light Railway was to ensure the necessary             districts with numerous small, manageable dwellings. The
access.                                                             anonymity suffered by the people in these “residential fac-
However, this transport system fell far short of meeting            tories” is criticized in particular – above all on account of
the requirements, as its capacity was far too low and it            the total isolation from other residents in order to avoid
lacked the essential connection to the London Under-                the stress of permanent contact.
ground. The road connections for private traffic and public         Organic, homogeneous population structures with their
buses were similarly inadequate. This made the Docklands            positive effects on social conduct are rarely found and the
unattractive to both commercial and private tenants. An             charge that high-rise apartment blocks are hostile to fam-
Underground link was finally built after extensive planning         ilies and children is consequently not entirely unfounded.
and at the enormous cost of roughly US$ 1.7bn; the road             Two diametrically opposed ghetto situations can easily
connections were likewise improved at the cost of almost            arise in high-rise apartment blocks: since the costs for con-
US$ 1bn. Only then did the precarious economic situation            struction and maintenance of these buildings are dispro-
of Canary Wharf improve.                                            portionately high, correspondingly high rents must be
As these examples show, almost every high-rise construc-            charged, with the result that these blocks are more or less
tion project is doomed to at least economic failure if the          reserved for the well-off, while the socially weaker classes
infrastructure is not considered, planned and actually in-          are excluded. Conversely, however, high-rise apartment
stalled down to the very last detail.                               blocks can rapidly cease to be attractive if compromises
                                                                    are made with regard to the building quality, maintenance
                                                                    or infrastructure on account of the high investment costs
                                                                    entailed. A building in disrepair will soon drive away the
2.5   Economic aspects                                              “good” tenants and become a slum.
                                                                    The ghetto situation is intensified when high-rise apart-
Hundreds of companies and thousands of people depend                ment blocks are built in newly developed fringe areas – far
on the smooth operation of a high-rise building, from the           away from cultural and social centres – on account of the
one-man business of a newspaper vendor or shoeshiner                high cost of land in inner city areas. It is not without good
and corporations with thousands of employees, such as               cause that these areas are commonly referred to as “dor-
banks, brokers or global players with a daily turnover in           mitory towns”.
the order of several billions to radio, television and tele-        Studies have also proved beyond all doubt that criminal
communications companies which use the roofs and tops               activity is promoted by huge apartment blocks and particu-
of high-rise buildings for the transmission and receiving           larly high-rise buildings. According to these studies, this
installations. In addition, there are innumerable other busi-       phenomenon is attributable to the anonymity of the resi-
nesses and workers with their families whose economic               dents, as well as to the “pro-crime” environment with ele-
situation is directly or indirectly linked with the high-rise       vators, poorly lit corridors devoid of human beings, refuse
building. These range from transport companies and                  collection rooms and bicycle garages, laundries and above
catering firms to tradesmen under long-term contract in             all underground parking lots. It is a proven fact that con-
the building.                                                       siderably more murders, burglaries, muggings, rapes and
Nor should it be overlooked that even the municipal au-             other crimes are committed in such buildings than in resi-
thorities and the service companies are also affected by            dential areas with smaller rented or private homes.
the “failure” of a high-rise building and that its effects can      Not only high-rise apartment blocks have a usually nega-
be felt nationwide or even worldwide in the worst case.             tive effect on people’s social environment: office towers
This scenario not only applies to such total failure as a           are equally disadvantageous. The vertical structure of the
2 High-rise buildings in the course of history, technology and the environment                                                           Page 22

buildings simultaneously underlines the vertical hierarchy:                      the possibility of falling objects. That fear is surely not en-
the location of the office space becomes an indicator of a                       tirely unfounded, for there have been cases in which parts
company’s “importance” and, if the company occupies                              of buildings, such as glass panes, have been torn out of
several or all the floors in a high-rise building, it may also                   their anchorage by strong winds and injured or even killed
be indicative of the employee’s standing in the company.                         people on the street below.
The company’s top executives reside on the uppermost                             Our love-hate relationship with high-rise buildings is final-
floors with the best views; the floors below provide a                           ly also revealed in such recent box-office hits from Holly-
shield and every employee can positively see the distance                        wood as “Deep Impact”, “Godzilla” or “Independence
between himself and “them up there“. It is therefore not                         Day”. It seems that their directors simply cannot avoid the
wrong to question whether high-rise office towers are                            temptation of reducing one of New York’s most beautiful
really appropriate to modern organizational structures                           buildings – the Chrysler Building – to a smouldering heap
with their emphasis on team work and interdisciplinary                           of rubble with the help of floods, monsters or meteorites.
cooperation.                                                                     As a result, these skyscrapers more or less become the
                                                                                 real stars of the film on account of their magic attraction
Excessive energy consumption is a major shortcoming of                           and immediate recognizability.
high-rise buildings and one which could possibly lead to
their demise one day. High-rise buildings are the farthest
removed from the ideal form as regards energy efficiency
– namely the sphere, or the cube in the case of houses.
That applies to both heating and cooling: some skyscraper
facades have to be cooled by day and heated by night in
order to avoid undue stresses and the resultant damage.
The World Trade Center, for example, consumes some
680,000 kWh/day electricity for air-conditioning during
periods of strong solar irradiation; the Messeturm in
Frankfurt burns up energy worth DM 40 per square metre
of useful floor space for heating and cooling every month.
A well insulated low-energy house, by comparison, uses
energy worth less than DM 1 per square metre. The “energy
balance” of high-rise buildings is also poor in other
respects such as the water supply, which usually only
operates with the aid of booster pumps, as well as in terms
of the disposal systems and operation of the elevators, etc.
From the point of construction economy in general, high-
rise buildings will probably always be the poorest conceiv-
able solution, from the particularly energy-intensive and
therefore expensive construction as such to the dispropor-
tionately high demolition costs. Moreover, high-rise build-
ings are made almost exclusively of materials which a
construction biologist would take great pains to avoid,
namely concrete, steel, light metal, plastics and a wide
variety of chemicals.
Although subjectively unaware of the fact, the residents
are frequently exposed to constant stresses in the form of
pollutant emissions and electrosmog. High-rise buildings
are sometimes described as microcosms; that is no doubt
meant in a positive sense, but the reality is different. The
people in a high-rise building are totally cut off from the
world around them, from wind and weather, from tem-
perature, from smells, sounds and moods. They live in an
artificial world.
At the same time, however, the high-rise buildings also
have a negative effect on the world around them, for they
not uncommonly generate air turbulence and downdrafts
in their immediate vicinity; they can be a source of un-
pleasant reflections and some adjacent areas remain per-
manently in the shade. Illuminated facades and large glass
fronts are a death trap for many birds.
The people outside the high-rise buildings also often have
the feeling that they are being observed or threatened by
3 Technology of high-rise construction

3.1 Planning                     3.2 Execution   3.3 Occupancy   3.4 High-rise construction in the future
Page 25                                                                                      3 Technology of high-rise construction

Skyscrapers are gigantic projects demanding incred-
ible logistics, management and strong nerves among
all concerned in their planning and construction.
As long ago as 1928, the American Colonel William
A. Starrett wrote that no peacetime activity bore
greater resemblance to a military strategy than the
construction of a skyscraper.

3   Technology of high-rise construction

3.1 Planning                                                    course of the entire planning and construction of a sky-
                                                                scraper project, it soon becomes clear that highly profes-
3.1.1 Planners                                                  sional management is essential for such a project. Project
                                                                management companies have come to play an increasing-
The complexity of the trades to be coordinated has be-          ly important role in recent years as they take over the en-
come several times greater since then. Take, for example,       tire organization, structurization and coordination of con-
the new block built for Südwest-Landesbank in Stuttgart:        struction projects. They act as professional representatives
many disciplines and different experts were involved sole-      for the client and embody the frequently voiced desire for
ly in the project planning:                                     the entire project to be coordinated by a single partner.
– Architects
– Planning engineers for the supporting structures (engi-       3.1.2 Regulations and directives
   neering design and structural analyses)
– Construction and site management (resident engineer)          The various laws, regulations, directives and standards in
– Planning of the technical building services (particularly     force must be taken into account when planning and erect-
   heating, ventilation, sanitation, cooling and air-           ing a building. The planning engineers are also obliged to
   conditioning)                                                observe what are known in Germany, for instance, as the
– Interior designers                                            “generally accepted technical rules for construction“; in
– Construction physics and construction biology                 other words, generally applicable technical and trade rules
– Planning and site management for data networks                must be taken into account and observed in addition to
– Planning of the lighting and materials handling               the standards and regulations.
– Planning of the electrical and electronic systems             Although each country has its own regulations and dir-
– Planning of the facades                                       ectives governing the construction of high-rise buildings,
– Surveying engineers                                           they are all basically similar in content with a few differ-
– Geotechnology, hydrogeology and environmental                 ences depending on the local circumstances. It is standard
   protection                                                   practice in some countries to base the bidding and plan-
– Design of outdoor facilities and vegetation                   ning phase for projects on foreign standards (particularly
– Surveying of the actual situation in surrounding build-       on the American ANSI Codes and UL Standards, British
   ings                                                         Standards or the German DIN standards) or to include var-
                                                                ious elements of these foreign standards in the national
If we were to include all the contractors and specialists in-   system of standards.
volved in the project as well, the list would probably be       As a rule, these regulations are primarily designed to en-
ten times longer. And if we then consider that bankers,         sure personal safety and then to protect the building
construction authorities, legal advisers and even advertis-     against damage and defects. In addition to the require-
ing agencies or brokers must also be coordinated in the         ments imposed by public authorities, there are also re-
3 Technology of high-rise construction                                                                                     Page 26

quirements imposed by insurance companies with the aim           This exceedingly concise outline of applicable regulations
of ensuring greater protection for property. These require-      illuminates only some of the rules to be observed when
ments can be classified in four groups:                          building a skyscraper. If all the regulations governing high-
                                                                 rise construction were to be stacked one on top of the
FIRE PROTECTION AND OPERATIONAL SECURITY                         other in printed form, they would themselves be as high
Many of the construction regulations concern fire protec-        as a multi-storey building.
tion. There can be many thousands of people in a high-
rise building at any one time. If a fire breaks out, they        3.1.3 Technical analyses and special questions
must all be able to leave the building in the shortest
possible space of time and without risk of injury. This is       Planning a high-rise building would be inconceivable
why regulations concerning the number and execution              today without the help of experts and technical consult-
of escape routes and fire escapes, fire compartments             ants. Extensive soil analyses are required to determine the
and the choice of materials must be observed (see                strength of the subsoil before deciding on the location for
Section 4.2.5).                                                  a high-rise building. In the majority of cases, cores are
Operational security encompasses regulations governing           drilled into the load-bearing subsoil to obtain soil samples.
the safety of elevators and escalators, the execution of         The drilling profile of the geological strata making up the
stairs, railings and parapets or the installation of emer-       subsoil and laboratory analyses of the soil samples pro-
gency lighting. Some regulations also include CO2 alarm          vide the basic data for the soil report which is in turn used
systems for underground parking lots; indeed, there are          as the basis for planning the supporting structures and
even regulations governing the non-slip nature of floor          choosing a suitable foundation structure with due regard
coverings in traffic areas, sanitary rooms and kitchens.         for the loads exerted by the high-rise building.
                                                                 The forces acting on the high-rise structure in the event of
STABILITY AND CONSTRUCTION PHYSICS                               an earthquake must be taken into account when erecting
The regulations governing the stability of a building are        high-rise buildings in areas prone to seismic activity. The
usually met by the requisite structural analyses. In add-        same applies to wind loads and particularly to the dynamic
ition to demonstrating the internal structural strength of       effects of windstorm or earthquake loads. The additional
the construction and safe transfer of loads to the subsoil,      vibration loads can result in overall loads of the same
the stability calculations must also include possible de-        order of magnitude as the load exerted by the dead
formation due to thermal expansion, wind loads and live          weight of the structure. The situation is particularly critical
loads or dead weight, for example. This is closely related       if the vibrations reach the resonant frequency of the build-
with demonstrating the safety of the construction, for in-       ing: in such a case, the vibrations can intensify until the
stance by taking steps to limit the (unavoidable) cracks in      entire building collapses. The collapse of the Tacoma
concrete elements.                                               Bridge in Washington State, USA, was probably the most
                                                                 spectacular case of destruction due to resonant vibration
PROTECTION AGAINST NATURAL HAZARDS                               in a man-made structure.
The regulations and directives governing protection              In many cases, these effects cannot be determined by or-
against natural hazards are usually closely associated with      dinary computation. Even computer simulation cannot al-
the demonstration of stability. Windstorms and earth-            ways help. Sometimes a decisive element may be lacking
quakes are the most serious natural hazards for high-rise        to obtain a mathematical approximation; in other cases,
buildings. As a rule, the assumed loads and design rules         the computer may be too slow or the storage capacity in-
for the “load cases” of earthquake and windstorm will be         adequate.
specified by the regulations in order to ensure that the         This frequently makes it necessary to carry out model
building will withstand windstorms or earthquakes up to          experiments in a scientific laboratory. Models of the high-
certain load limits. At the same time, this will serve to rule   rise buildings are exposed to artificial earthquakes on a vi-
out the risk of bodily injury due to falling parts of the        bratory table or subjected to a simulated hurricane in the
building, especially parts of the facade.                        wind tunnel. A detailed knowledge of mathematics and
                                                                 physics is necessary to ensure that the same physical
SOCIAL ASPECTS AND PROTECTION OF THE SURROUNDINGS                properties and serviceable results are obtained despite the
The regulations governing social aspects and protection of       reduction in scale. For this reason, these studies can only
the area surrounding high-rise buildings are designed            be carried out by highly specialized test institutes.
above all to prevent any indirect risk or threat to people.
Such regulations may concern planning aspects, such as           3.1.4 Construction licensing procedure
the minimum distance between a high-rise building and
neighbouring buildings, or they may take the form of rules       The construction licensing procedure is normally specified
defining the maximum permissible influence that a build-         in the construction laws of the country concerned. As a
ing can have on the microcosm surrounding it.                    rule, the principal will file an application with all the requis-
Depending on the location of the high-rise building, cor-        ite documents (description, plans, analyses, etc.) to the
responding statutory instruments may also govern the             relevant construction supervisory authority. The involve-
effects on air traffic safety or the building’s influence of     ment of specialists is obligatory in the case of larger and
radio communications.                                            more complicated projects, such as those involving high-
3 Technology of high-rise construction   Page 28
Page 29                                                                                           3 Technology of high-rise construction

                                                                     rise buildings. Such specialists include experts from the
                                                                     municipal fire brigade, water authorities, trade supervisory
                                                                     offices, environment protection agencies or similar offices
                                                                     in other specific fields.
                                                                     These specialists review the applications for a construction
                                                                     licence and specify any additional requirements to be met.
                                                                     The licence is then sent to the principal together with the
                                                                     requirements specified by the specialists; responsibility for
                                                                     complying with these requirements rests with the principal
                                                                     or owner of the building.

                                                                     3.1.5 Other constraints

                                                                     Even in our high-tech era, the planning and construction
                                                                     of a high-rise building are not dictated only by naked fac-
                                                                     tual constraints. Tradition, religion and even the belief in
                                                                     spirits and demons still play a not insignificant part in
                                                                     many countries.
                                                                     Take, for example, the Hong Kong and Shanghai Bank
                                                                     building in Hong Kong: during the planning phase, a geo-
                                                                     mancer or expert on “fung shui” (i.e. “wind and water“)
                                                                     repositioned the escalators and moved executive offices
                                                                     and conference rooms to the other side of the building on
                                                                     the basis of astrological investigations and measurements
                                                                     in order to guarantee an optimum sense of well-being for
                                                                     clients and employees. However, it must be said that such
                                                                     intervention is limited by technical and structural require-
                                                                     In western countries, too, the owners are guided by
THROUGH                                                              similar considerations when the 13th floor is omitted
                                                                     from the planning or the technical installations are deliber-
                                                                     ately located on this floor in order to avoid the unlucky
                                                                     number 13.
Page 31                                                                                    3 Technology of high-rise construction

3.2 Execution                                                 conditions prevailing on site. Drilling piles in a whole var-
                                                              iety of forms can be used when working with large pile
3.2.1 Foundations                                             diameters and very long piles. Modern equipment can
                                                              easily ram piles measuring up to 2 m in diameter to
Although the foundations are out of sight once the build-     depths of well over 50 m. The piles are then combined
ing is completed, they are of immense importance for en-      into appropriate pile groups in accordance with the loads
suring that the dead weight and live loads of the building    to be transmitted by the building.
are safely transmitted to the native subsoil.                 Although the load-bearing capacity can be roughly calcu-
These loads are not inconsiderable. The dead weight of a      lated on the basis of soil characteristics, the maximum
high-rise building can amount to several hundred thou-        permissible pile load is determined by applying test loads
sand tonnes. This value may be exceeded several times         to the finished piles with the aid of hydraulic presses and
over by the live loads which are taken as the basis for de-   comparing the resultant settlement with the permissible
signing the building and include the loads from equipment     settlement.
and furnishings, people or moving objects, as well as wind    Diaphragm walls are another means of producing deep
or earthquake loads. Moreover, these loads often exert dif-   foundations. These walls are produced directly in the
ferent pressures on the subsoil, thus resulting in uneven     ground and are between 60 and 100 cm thick. They are
settlement of the building. In order to avoid such develop-   produced in sections with the aid of special equipment
ments where possible, these buildings must be erected on      and a stabilizing bentonite slurry. The result is a continu-
subsoil of high load-bearing capacity, such as solid rock.    ous wall in the ground. This method is used in particular
Yet even if a strong native subsoil is found near the sur-    when subsoil of high load-bearing capacity is only found
face, shallow foundations will frequently be disregarded in   at considerable depth.
favour a system that transfers the load to deeper layers on   Diaphragm walls and piles are also used to safeguard the
account of the high bending moments to be absorbed            foundation pit required for construction of the under-
from horizontal forces.                                       ground part of the building. The effort entailed can be con-
This can be done in several ways. One is to produce round     siderable, particularly if the neighbouring buildings are
or rectangular caissons which are lowered to the required     very close. Rotating drills are mostly used today to minim-
depth and bear the foundation structure. Pile foundations     ize vibrations when installing the retaining wall. Founda-
are probably the most widely used method, however. The        tion pits can easily be produced to depths of 30 m or more
piles can either be prefabricated and then inserted in the    using this method.
native soil or they can be produced on site in the form of
concrete drilling piles. Which method is chosen will ultim-
ately depend on both the structural concept and the soil

3 Technology of high-rise construction                    Page 34


Page 35                                                                                         3 Technology of high-rise construction

3.2.2 Supporting structure                                        such an outrigger truss yields further advantages over a
                                                                  simple core construction when it comes to transmission of Load-bearing parts                                        the horizontal loads. The bending stress applied to the
                                                                  core area in the lower floors is considerably reduced when
The steel skeleton permitted hitherto inconceivable flexi-        using an outrigger truss. The outrigger itself usually ac-
bility in construction and layout planning. It also permitted     commodates such technical floors as the heating and ven-
series construction up to great heights, since the vertical       tilation systems.
dead weight was considerably lower than when using                The Fort Wisconsin Center built in Milwaukee in 1962 is
solid masonry and did not make it necessary to grade the          one example of an outrigger truss structure. The produc-
sectional steel profiles in these areas. The tradition of steel   tion of such suspended structures gave rise to a number
skeleton structures predates the first high-rise building to      of innovations, such as the lift-slab process for concrete
have been erected by this method, namely the Home In-             structures. The load-bearing cores are first of all erected
surance Building in Chicago (1885): mills and granaries, as       with the outrigger on top; the individual floors are then
well as engineering structures (bridges, silos) had already       concreted on the ground, one above the other (separated
been built in England with an iron framework towards the          by a release spray). Finally, they are raised to their installa-
end of the 18th century.                                          tion position by means of hydraulic jacks and then con-
The first frame structures used for the steel skeleton            nected to the core (see Section
were flexurally rigid frames corresponding in height to           Supporting steel structures in the form of tubes are often
one floor. New York’s Empire State Building, which was            used for extremely tall buildings. In this case, the support-
completed in 1932, is one example which clearly shows             ing structure is located in the outer facade, which is conse-
the advantage of this new method, namely the short                quently designed in the form of a load-bearing facade with
time required for the construction work. Moreover, the            small openings. The result is an enclosed, intrinsically
complete separation of outside wall and supporting                rigid tube without any unnecessary space-filling columns
structure permitted absolute freedom of design for the            inside. The World Trade Center in New York is an example
facade. Instead of requiring around 300 kg of steel per           of such a structure. The outer walls are studded with verti-
square metre of base area as in the past, modern support-         cal steel columns roughly one metre apart. A generously
ing structures only require roughly 125 kg of steel on            dimensioned development area was obtained on the
average.                                                          ground floor by “collecting” the descending columns.
As the buildings became taller and taller, however, the           America’s tallest skyscraper, the Sears Tower in Chicago
main problem was no longer the vertical loads but such            (443 m high), is a further development of the conventional
horizontal loads as wind and earthquake forces, as well as        tube: it is a “bundled” tube. The layout of the building is
their transmission.                                               subdivided into a number of tubes to relieve the columns
This led to the development of what was known as the              in the corners of the building when subjected to horizontal
core method. The individual floors with their secondary           loads; this results in more uniform distribution of the load
supporting structure, namely the columns, are suspended           over the facade columns. In this case, however, the inter-
from a central core as the primary supporting element,            ior can no longer be designed with the same flexibility as
normally in the form of a reinforced concrete or steel            when using a single tube.
structure with reinforcing shear walls. The columns merely        The “truss tubes” perfected by Fazlar Khan (SOM) in the
transmit vertical loads, while the core transmits both verti-     John Hancock Center in Chicago are another further devel-
cal and horizontal loads. Its primary function is to rein-        opment of the basic tube. These tubes are additionally re-
force the building in horizontal direction. The cores and         inforced by diagonal struts in the facade plane and are a
their surrounding walls normally accommodate vertical             structural feature that has almost become a hallmark of
service installations, such as elevators, stairs, primary ser-    SOM buildings.
vice shafts for electric power and HLS (heating, lighting,        It was only in the mid-1970s that concrete began to be
sanitation). A similar supporting effect is obtained with the     more widely used in constructing skyscrapers. Until then,
aid of horizontal reinforcing elements in the form of shear       the length of time required for concrete construction and
walls, which may be considered as an “open core“. How-            the associated financing problems were the main reasons
ever, such supporting structures are rarely found in taller       for the predominant use of steel structures in the construc-
buildings.                                                        tion of high-rise buildings. New developments in shutter-
Since the middle of the 20th century, a number of im-             ing, however, resulted in dramatically shorter construction
provements in the supporting structures for skyscrapers           times. The octagonal concrete core of the Messeturm in
have been introduced by the architects Skidmore, Owings           Frankfurt, for example, was erected with the aid of a slip-
& Merrill (SOM) in Chicago. One such development by               form which was hydraulically raised one metre every day.
SOM is the “outrigger truss”: a rigid superstructure known        The latest developments in supporting structures for high-
as the outrigger is mounted at the top of a reinforcing core      rise buildings include composite structures of steel and
with movably connected floors and columns. The outrig-            concrete, for instance in the form of steel sections embed-
ger connects the columns to the core. They are suspended          ded in concrete.
from the outrigger and are therefore under tension, thus
eliminating the risk of buckling that is associated with
pressure elements. A supporting system in the form of

A   B   C   D        E                 F                  G

                                                    OUTRIGGER TRUSS METHOD
                                                         BUNDLED TUBES (F-G)
   3 Technology of high-rise construction                            Page 40

                                                            B Wind

Page 41                              3 Technology of high-rise construction


3 Technology of high-rise construction                                                                                     Page 42 Special construction methods                           glazing during construction of the supporting cross. The
                                                               finished floors were then connected to the supporting
BMW HEADQUARTERS, MUNICH                                       cross via the king posts and raised one floor at a time
The headquarters of BMW A.G. differs from conventional         every week with the aid of hoisting gear so that another
buildings to create an impressive corporate symbol in the      floor could be produced in the space vacated at the foot of
form of a 100-m-high four-cylinder structure. The require-     the core and then connected to the floor above (lift-slab
ments for appropriate office organization yielded a basic      method). Completion of the facade, glazing, installation
outline in the shape of a clover leaf. Stairways, elevators    and interior finishing proceeded on the suspended floors,
and sanitary areas are accommodated in the central core.       unimpeded by the structural works and lifting operations.
In this way, all the offices can be reached by the shortest    In addition to reducing the construction time required, this
possible route. Trendsetting methods were also used for        method also eliminated the need for expensive tooling
the construction work.                                         and assembly work.

A reinforced concrete version was chosen as the most           LA GRANDE ARCHE, PARIS
economical solution. According to the design concept, the      This building, which has already been mentioned in Sec-
entire building with 18 office floors and a technical floor    tion 2, takes the form of a giant cube open on two sides
was to be suspended from a girder cross at the top of the      with edge lengths of 110 m. It was completed at the end of
roughly 100-m-high core via four central king posts. This is   1989 on the 200th anniversary of the French Revolution
a modification of the outrigger truss (Section The   and took 5 years to build (see photo on page 18).
entire load of the building is transmitted to the founda-      The building has a weight of more than 300,000 Mp and is
tions via the core as the central element; it also absorbs     mounted on neoprene bearings, the loads being transmit-
all wind forces. A mighty girder cross with a projection of    ted 30 m into the subsoil via twelve concrete pillars.
16 m is mounted at the top of the core.                        The cube’s main support is in the form of four prestressed
The four king posts are secured to this central girder         upright reinforced concrete frames 21 m apart. They are
cross, each king post comprising 105 threaded steel bars       complemented by horizontal members measuring roughly
with a load-bearing capacity equal to a suspended weight       70 m at ground and roof level. Each of these members is
of 4,600 Mp. Small outer columns are additionally located      9 m high, the equivalent of a 3-storey building. Since the
between the floors. These outer columns are designed as        two vertical sides of the cube would be without roof-level
compression columns above the technical floor (12th            transverse bracing during construction, the required stabil-
floor) and as king posts below.                                ity for that phase of the work was produced by means of
Time and costs were the decisive reasons for choosing          horizontal steel truss reinforcements.
this innovative construction method. All 19 floors were        A total of 37 office floors are accommodated in the
successively produced at the foot of the shell and core; the   two 18-m-wide wings of the cube (each with an area of
first floors were even produced complete with facade and       42,000 m2).

                                                                                           Top: VIEW FROM THE HEADQUARTERS BUILDING
                                                                                      Bottom: 32 HEADQUARTERS OF BMW A.G. IN MUNICH
Page 45                                                                                     3 Technology of high-rise construction Facade                                                 metal facades are at least the equal of conventional con-
The skeleton construction which has increasingly been          Modern facades also require a sophisticated ventilation
used since the turn of the century has inevitably given rise   and cooling system. The air-conditioned or twin facade is
to new possibilities for the facade. The size, shape and       a case in point. Here an additional facade of laminated
number of windows were no longer limited by structural         glass is arranged in front of the conventional facade, thus
requirements following the introduction of curtain facades,    creating a space through which air can circulate. More
since the loads were now primarily transmitted by posts        complex ventilation concepts for routing air into and out
and columns.                                                   of the building may be realized by including additional
                                                               vertical and horizontal bulkheads. Individually controlled
PLANNING                                                       ventilation flaps are capable of providing a more natural
Most facade designs today are still based on empirical         and far less complex exchange of air.
know-how and are not tested until the design has been
established in detail. The tests are carried out on true-to-   PRODUCTION AND ASSEMBLY
scale models of individual facade elements in order to         Due to the extensive know-how required with regard to
test adequate resistance to air and water, load-bearing        material properties and construction physics and on ac-
capacity and the possibility of excessive deformation          count of the great manufacturing depth, modern facades
or glass breakage when subjected to corresponding loads,       are only produced by specialized companies based on the
e.g. with the aid of firmly anchored aircraft engines.         architect’s design and in accordance with functional, as
                                                               well as structural aspects before subsequently being as-
DESIGN                                                         sembled.
Today’s modern facades are characterized by external wall      The degree of prefabrication in modern facades is consid-
elements equal to one floor in height and inserted             erable. The frames, glazing, parapet lining, sunshades and
between the respective structural floors. Non-supporting       anti-glare finish, as well as thermal insulation and sealing
metal facades suspended in front of the building have in-      are all assembled into single-storey facade elements in the
creasingly become established for economic reasons, par-       manufacturer’s plant. In many cases, such technical equip-
ticularly in high-rise construction.                           ment parts as radiators, air outlets and the ducting for
The scope for design is enlarged by coloured or mirrored       electrical and electronic equipment are also already inte-
window panels and linings of natural stone, ceramic            grated at this stage.
tiles or brick. Almost any desired appearance can be pro-      In the meantime, fixing elements can be mounted on the
duced.                                                         shell of the high-rise building. These elements can usually
                                                               be displaced in three planes to compensate the dimen-
TECHNICAL PROPERTIES                                           sional tolerances occurring in the shell. The facade elem-
Modern facades must meet complex requirements as re-           ents as such are fitted without the help of scaffolding,
gards construction technology, engineering design and          thus greatly reducing the time required for this work. The
construction physics. Thanks to its lightness and almost       frame profiles are assembled with labyrinthine indenta-
unlimited possibilities for profile design, aluminium has      tions to compensate the deformation arising in the build-
largely become the material of choice for the outer frame-     ing as a result of wind and live loads, as well as tempera-
work. The panes are made of high-grade glass filled with       ture differences. Permanently elastic rubber profiles en-
noble gases or with a surface coating that reflects infrared   sure that the facade remains impermeable to air and
light. On the inside, modern facades are highly imperme-       water.
able to water and water vapour in order to prevent dam-
age due to moisture.
Despite the large areas of glass, protection against the sun
is more important than heat loss today due to good ther-
mal insulation of modern facades. Even where sound-
proofing and fire protection are concerned, glass and

3 Technology of high-rise construction                                                                                     Page 46 Roof                                                     Due to the relatively small area available per floor, fire-
                                                                 resistant elements (fire walls) are usually only to be found
There are no fixed rules governing the roofs of high-rise        in the core areas incorporating the elevators, stairwells,
buildings. The roof design depends only on the architect’s       service and installation shafts, sanitary and ancillary
draft and on the purposes and functions to be fulfilled by       rooms. A vertical breakdown into fire compartments is
the roof.                                                        mostly obtained with the aid of fire-resistant floor con-
Most roofs are flat. The electromechanical drive system          structions (for further details see Section 4.2.4).
for the elevators is usually installed on the roof; in some      The installations for air-conditioning, ventilation, lighting
cases, there is also a rail around the perimeter of the          and fire alarms are usually located between the load-bear-
building to accommodate the equipment required for               ing ceiling and a suspended false ceiling into which the
cleaning the facade, as well as the pertinent connections        lamps are normally integrated. Small-scale electrical in-
and facilities.                                                  stallations are contained in trunking in the screed flooring;
A heliport or parking space can also be set up on the flat       elevated false floors are installed if numerous connections
roof of large high-rise buildings. It is sometimes even used     are required, such as in computer centres. Cables can then
in Japan for golfing practice.                                   be routed as desired in the space below the floor; the
Air-intake towers for air-conditioning systems, on the           equipment is connected to sockets in so-called floor tanks.
other hand, have become less common on modern high-              False floors are to be found almost everywhere in modern
rise buildings. Due to the great height of buildings, air-       office towers, since cables can be rerouted without diffi-
conditioning and heating systems are now decentralized           culty, as is increasingly required on account of the rapid
and spread over several individual floors. Moreover, every       pace of change in office and communications technology.
installation and every superstructure on the roof means          Moreover, the space below the floor can also be used for
another opening in the intact roof skin and this can give        ventilation and air-conditioning installations, particularly in
rise to leakage problems, particularly on flat roofs. It is      computer centres. Particular attention must be paid to the
therefore advantageous to transfer such systems to lower         question of fire protection in such false floor construc-
floors.                                                          tions.
Overhead glazing is another type of roof commonly found          Connection of the flexible partition walls to both the sus-
in high-rise buildings. Such roofs keep out the elements         pended ceiling and the elevated false floor can pose prob-
while at the same time creating spacious assembly areas,         lems. From the point of view of soundproofing and ther-
usually in the centre of the building. Atriums and conven-       mal insulation, it would be better to install the partition
tion halls are two pertinent examples.                           walls between the load-bearing floors. However, since the
High-rise buildings with a sloping roof are usually round-       suspended ceilings and false floors normally extend over
ed off by an antenna system with appropriate lightning           the entire area and are not confined to any single room on
protection.                                                      account of the technical installations, the partition walls
                                                                 must also be fitted between the suspended ceiling and
3.2.3 Interior finishing                                         false floor. This consequently makes it necessary to use
                                                                 soundproofing and thermally insulating floor coverings,
Walls, ceilings and floors in high-rise buildings are no dif-    as well as ceiling materials.
ferent to those in other buildings. The choice of materials      Facade elements into which technical components have
and structures depends on the intended use of the build-         already been incorporated by the manufacturer (see
ing rather than on its form (high-rise, low-level or cubic).     Section 3.2.3) are conveniently linked to the remaining net-
Since particular importance is attached to flexible use of       work by means of screw-in and plug-in connections. How-
high-rise buildings, the partition walls, floor structures and   ever, it is becoming increasingly rare for such technical
(usually suspended) ceilings will be of corresponding de-        service connections to be installed in the external walls,
sign.                                                            as they do not permit as flexible use of the room as floor
When considering the interior finishing, a distinction must      tanks.
basically be made between load-bearing or supporting ele-
ments which are required for structural reasons and those
which merely partition off the rooms and installations.
Load-bearing elements are almost exclusively made of
concrete or steel today, as well as of combinations of
these materials.

                                                                                                              34 CEILING INSTALLATION
                                                                                                                  35 DOUBLE FLOORING
3 Technology of high-rise construction                                                                                 Page 48

3.2.4 Service systems                                            – It must be possible to shut off individual plant segments
                                                                   when the corresponding parts of the building are not in Installations                                              use.

ENERGY AND WATER SUPPLY                                          SUPPLY OF HEAT AND COOLING
Unlike the case with normal multi-storey buildings, the          Unlike the case with the majority of normal multi-storey
technical service components in high-rise buildings must         buildings in which the installed heating capacity is several
meet special requirements – if only on account of the            times the required cooling capacity, the ratio is normally
height – since the required supply of energy, water and air      reversed completely in most high-rise buildings, due
and the effluent volume are incomparably larger. The twin        above all to the larger ratio of window area to total ex-
towers of the World Trade Center in New York, for in-            terior area.
stance, with around 50,000 employees and 80,000 visitors         The energy required for this purpose, such as heating,
every day, requires more than 25,000 kWh of electricity          steam, refrigeration and electricity, must be supplied with
every hour. These utilities must also be transported to the      due regard to cost-efficiency and the minimum possible
very last floor in sufficient quantities, under adequate         environmental impact due to emissions. A number of
pressure and at sometimes totally different temperatures.        alternative solutions are drawn up during the planning
The planning effort required on the part of the service en-      phase and compared in order to determine the most cost-
gineers responsible for the supply and disposal services in      efficient source of energy on the basis of the investment
high-rise buildings is therefore very much greater than          costs and expected annual costs for operation and main-
in the case of smaller and medium-sized projects. The            tenance of the equipment.
costs for electrical and electronic systems in the recently      The essential difference between high-rise buildings and
completed Petronas Towers in Kuala Lumpur, currently the         other buildings in terms of designing the components
tallest building in the world, amount to more than US$ 90        (particularly fittings, pumps, gaskets) lies in the higher
per square metre – and that does not include any other           pressure stage. A water column in a 300-m-tall building,
services.                                                        for instance, exerts a stagnation pressure of 30 bar. The
The pressure load on the individual components is re-            fittings on the lower floors must therefore be dimensioned
duced through subdivision into several pressure stages           for the maximum stagnation pressure (possibly with the
with technical service centres in the basement or on the         aid of pressure reducers). This makes for a major differ-
ground floor, on intermediate floors and on the roof.            ence in costs.

The systems should be designed in such a way as to en-           Pressure stages are also required for the sanitation, thus
sure flexible division of the areas (large rooms, individual     permitting the use of smaller pumps. Sanitary dispensing
rooms) so that their use can subsequently be changed             points must additionally be isolated from the building as
without extensive conversions.                                   such for soundproofing reasons.
A variety of ventilation and air-conditioning systems can        The internal heat loads (e.g. hot exhaust air, exhaust heat
be installed, depending on the purpose for which the             from refrigeration systems) accumulated in high-rise
building is used. The high-rise headquarters of the Deut-        buildings are commonly used to heat water with the aid of
sche Bank in Frankfurt am Main, for instance, is supplied by     heat pumps or heat recovery systems.
a two-channel high-pressure system in which the air is in-       Studies undertaken in the USA have shown that the height
jected from above and discharged through corresponding           does not have any effect on the flow rate and rate of fall,
exhaust air windows. A second, independent two-channel           since faecal matter and effluent do not simply drop to the
high-pressure system additionally blows air into the             ground under the force of gravity, but more or less wind
rooms from the false floors.                                     their way downwards along the pipe walls.
The concept used in the Messeturm in Frankfurt am Main
is completely different: in this case the required air is sup-   CONTROL SYSTEMS
plied via what is known as a one-channel continuous-flow         Today’s complex, ultra-modern control systems are pri-
system in combination with a “fan-coil four-conductor            marily based on intelligent digital controllers. This tech-
system” in the outer facade.                                     nology permits a direct link between DDC (direct digital
In principle, all air-conditioning and ventilation systems       control) substations and the centralized instrumentation
must meet the same basic requirements:                           and control which also takes over energy management
                                                                 functions, such as:
– The air in the room must be continuously renewed (a            – optimization of the overnight and weekend temperature
  three to sixfold exchange of air is normally required per        reduction,
  hour).                                                         – linking the heating of service water with re-cooling of
– The outside air flow must be guaranteed with a min-              the refrigeration system,
  imum fresh air flow of 30 to 60 m3/h per person.               – operation of the external blinds.
– The risk of drafts must be minimized and any nuisance
  due to the transmission of sound eliminated.
Page 49                                                                                     3 Technology of high-rise construction Deliveries, vehicles                                   It is therefore not unfair to assert that the American invent-
                                                               or of our modern “safety elevator”, Elisha Graves Otis,
Although most high-rise buildings are centrally located        was also one of the pioneers who paved the way in 1852
and within a convenient distance to public transport           for high-rise construction. Asked what they feared most in
systems, a sufficient number of parking spaces must still      a high-rise building, the respondents claimed that their
be provided for employees, suppliers and visitors. The         greatest horror scenario was not a fire, but a malfunction
number of parking spaces required is usually stipulated in     in the elevator system. Such catastrophes may be exceed-
the construction regulations in relation to the number of      ingly rare, but they cannot be excluded entirely. A fully oc-
jobs or useful office space; similar ratios also apply to      cupied elevator plummeted when a B25 bomber crashed
other business premises, shops, restaurants and meeting        into the Empire State Building in 1945 (see Section 4.8.2).
halls. The ratio may be more than 5:1 – i.e. one parking       In the beginning, when the high-rise buildings had no
space for more than five jobs – if the building is well sup-   more than about 20 floors, every elevator led from the en-
plied by public transport, such as direct connection to the    trance level (not necessarily the ground floor) to every
underground railway. Even in such cases, however, sev-         other floor in the building. The simple control technology
eral hundred or a few thousand parking spaces may still        was offset by a number of disadvantages: numerous ele-
be required for large high-rise buildings. The recently com-   vators and elevator shafts were needed. The numerous
pleted Petronas Towers in Malaysia, for instance, is set to    stops and, above all, the low speed (with frequent braking
accommodate around 70,000 workers. In extreme cases, if        and restarting) meant that it took a long time for the eleva-
adequate public transport is not available, it may be ne-      tor to reach its destination. It was soon found that eleva-
cessary to provide one parking space for every job.            tors – like every mass transit system – needed a sophisti-
                                                               cated operating concept. The two operating systems com-
For financial reasons, the size of a high-rise building is     monly used today – namely group and changeover opera-
often also dictated by the number of parking spaces re-        tion – only became possible with the development of
quired. Depending on the nature, location and execution        powerful drive systems and controllers, as well as highly
of the garages and on the building’s structural system (na-    effective braking systems with multiple braking for safety
ture of the subsoil), the manufacturing costs for one park-    reasons.
ing space can easily amount to around DM 50,000. This          In group operation, for which a separate shaft is (still) re-
means that the cost of building 2,000 parking spaces can       quired for each elevator, the elevators or groups of eleva-
reach as much as DM 100m with complex engineering and          tors only serve certain floors: one group of elevators
location on several levels, including the required ramps       serves the first ten floors, for example, while a second
and traffic areas.                                             group serves floors 10 to 20 from the entrance level, the
Traffic links must be created not only for the parking         next group then serves floors 20 to 30, etc. The groups
spaces, but also for delivery traffic to the building, as      must overlap on at least one floor so that people can
well as for refuse-collection vehicles. High-rise buildings    transfer from the 17th to the 23rd floor, for example, al-
are commonly said to represent a “town under one               though they must change elevators in the process. The
roof“. That, however, also means that the traffic to,          advantage of this system is that the number of elevator
around and from the building is equal to that of a small       shafts decreases towards the top of the building, thus
town, the only difference being that the entire traffic is     counteracting the lower floor space frequently found on
concentrated on a handful of access roads and adjacent         the top floors.
traffic areas which must be able to handle this volume         In changeover operation, large and very fast express ele-
of traffic at peak periods.                                    vators serve a small number of central floors which are
                                                               often also highlighted architecturally. In New York’s Em- Passenger transport, vertical development              pire State Building, these elevators take no more than a
                                                               minute to travel from the ground floor to the 80th floor.
In addition to escalators and automatic walkways, which        “Local elevators” serve the floors between the “change-
usually only serve to connect a few floors conveniently        over floors“. Here too, the elevators may serve groups of
and without delays, passengers and goods are normally          floors in exceptionally large high-rise buildings. If the
carried up and down by elevators in high-rise buildings.       equipment rooms are located alongside the elevator shaft,
The comparison made above between a high-rise building         a number of local elevators can be operated one above
and a small town also applies with regard to the number        the other in the same shaft; in this way, the number of
of people inside the building: in the course of a few hours    shafts can be reduced while maintaining the transport
every morning, tens of thousands of people stream into a       capacity. Up to three elevators are contained one above
megabuilding to start work and leave again within a very       the other in each of 36 open shafts in New York’s World
short space of time at the end of the day. They are supple-    Trade Center. The volume of traffic is analysed by micro-
mented by visitors, guests and customers, with the result      processors, thus avoiding long delays. The floor area has
that the elevators often have to transport well over           been increased by 25% as a result of these sophisticated
100,000 people every day.                                      systems.
3 Technology of high-rise construction                                                                                    Page 50

At least one goods elevator with high load-bearing cap- Waste disposal
acity and therefore lower speed is usually required to
transport goods and to serve the building.                       In the days when waste was collected without preliminary
Depending on the size of the high-rise building, there           sorting on site, waste chutes were frequently installed in
must also be a sufficient number of elevator cabins large        residential and administrative buildings, as well as in high-
enough to accommodate stretchers.                                rise buildings with up to 20 floors. Such waste chutes are
Elevators should never be used to evacuate people follow-        not advisable in taller buildings – due to the associated
ing a catastrophe. It is therefore a statutory requirement in    greater height of fall – for paper or plastic bags tear open
most countries that a warning be affixed to all elevators        as they fall and considerable noise is generated by the
prohibiting use of the elevator in the event of a fire. Eleva-   waste as it falls and collides with the walls and bottom of
tors are often directed automatically to the ground floor        the chute. The fire hazard is also enormous.
following a fire alarm and remain there with their doors         Standard practice today is to collect the waste separately
open. So-called firemen’s lifts are additionally installed in    on each floor: paper, recyclable secondary materials, com-
high-rise buildings for use in the event of a fire (see Sec-     postable organic waste and residual household waste
tion 4.2.4).                                                     which is collected in large containers and then transferred
Apart from the statics, there is no other structural part or     via the goods elevator (or service elevator) to a central col-
equipment in a building subject to so many regulations           lecting point (in the basement) alongside the delivery area
and technical controls as the elevator – and with good           or to the underground parking deck. The waste is com-
reason, too. Constant care and regular maintenance com-          pressed to a fraction of its original volume in special con-
bined with stringent inspections by an independent test          tainers at the central collecting point. Mobile waste collect-
institution, such as the Technical Inspection Agencies (TÜV)     ing bins are ready and waiting in the goods elevators in
in Germany, are an absolute must for the safe operation of       the World Trade Center in New York, for instance. In add-
high-rise buildings.                                             ition, there are five filling hoppers which can comminute
                                                                 all manner of objects, including desks.

Page 51                                                                                        3 Technology of high-rise construction

Too little attention is frequently paid to the problem of        nal service-providers (“outsourcing“). Both alternatives re-
waste disposal when planning a building. The following           quire an efficient building management capable of taking
rough estimate illustrates just how much waste can accu-         over the following responsibilities, particularly in the case
mulate in a high-rise building: if each of the 5,000 as-         of high-rise buildings:
sumed employees in a high-rise building “produces” only          a) Technical building management
2 kg of waste per day, that makes a total of no less then        – Energy supply
10 tonnes to be disposed of every day. In addition, there is     – Disposal
the waste from shops, kitchens and restaurants, as well as       – Equipment operation
special waste from service facilities and filling stations for   – System communication
motor vehicles. A sophisticated logistical system is conse-      b) Commercial building management
quently needed simply to dispose of the waste.                   – Cost accounting
                                                                 – Property accounting
                                                                 – Rentals
                                                                 – Contract management
3.3 Occupancy                                                    c) Infrastructural building management
                                                                 – Cleaning services
3.3.1 Maintenance, administration                                – Caretaker services
                                                                 – Security services
When the high-rise building is completed, it is taken into       – Secretarial and postal services
service and occupied by the owner or tenants. Costs are          A new market segment known as “facility management”
continuously incurred during this time for maintenance           has developed in recent years and caters to the needs of
and care of the building; these costs can have a significant     users in larger properties in particular. It differs from clas-
effect on the financial result of the building’s operator. He    sic building management in that it is not limited solely to
must decide whether to employ his own staff to deal with         the occupancy phase, but is already in action during the
the problems (e.g. cleaning, maintenance, security, admin-       planning phase and therefore covers the entire life cycle of
istration) or whether to assign intrinsic functions to exter-    the building right up to its demolition.

37 ELEVATOR DEMONSTRATION BY OTIS                                38 MAINTENANCE
3 Technology of high-rise construction             Page 52


Page 53                                                                                      3 Technology of high-rise construction

Cost-efficient optimization of all processes during the         special precautions must be taken and the work efficiently
occupancy phase of a high-rise building requires an effi-       coordinated to ensure that the conversion proceeds with-
cient and powerful computer system including CAD                out a hitch.
(computer-aided design) applications. The latter is             The only possibility for expansion in densely populated
particularly important for internal planning changes, con-      cities is normally upwards – i.e. by adding floors – if add-
versions, rehabilitation and changes in occupancy, as well      itional space is required at a later date. In such cases, par-
as for permitting documentation of important information        ticular care must be taken to ensure that the additional
(e.g. layout drawings, general drawings of the building,        loads can be absorbed by both the existing building and
security information, furniture inventories, telephone con-     the existing foundation structure. It may even prove ne-
nections).                                                      cessary to extend the foundations in such a case. This can
New requirements are often imposed on the performance           be achieved by a technically complex method using add-
of technical equipment in a high-rise building in the           itional piles which must be produced with the aid of spe-
course of its occupancy phase. Different times of day and       cial drilling equipment in the underground parking levels
seasons, as well as changing tenants require rapid adapta-      on account of the low working height.
tion of the heat, cooling, electric power and lighting. In      Demolishing old skyscrapers in inner city areas is an ex-
office buildings, manufacturing premises and high-rise          ceedingly complicated business. Such buildings are nor-
buildings, this adjustment is handled by freely program-        mally demolished by blasting after months of preparation
mable DDC systems which record all the data of the con-         and a great deal of expert knowledge so that the explosive
nected technical equipment, such as fans, burners, pumps,       charges are positioned at precisely the right points to en-
valves and external blinds, analyse these data and then         sure that the building collapses like a stack of cards with-
optimize the corresponding process sequence. Unneces-           out a single piece of rubble leaving the site.
sary energy consumption is avoided, consumers are
switched off when their offices are not in use and              3.3.3 Rehabilitation
switched on again shortly before occupancy recom-
mences. The recorded data are forwarded to either the           There are many reasons why a high-rise building should
centralized instrumentation and control in the building or      have to be rehabilitated. The criteria to be met here are
via the public telephone network to an external control         basically the same as for conversions, i.e. the safety of
centre. Expensive call-outs on site can be reduced              the building and its residents or users must be assured
through remote programming by the maintenance com-              completely and at all times during the rehabilitation work.
pany if faults arise or limit values change. If more com-       Particularly high safety standards must be maintained in
plex maintenance work is required, the technician on duty       conjunction with asbestos abatement – i.e. when removing
can immediately see which spare parts are required              the asbestos installed as insulation or for fire-protection
to remedy the fault.                                            purposes and replacing it with physiologically safer
                                                                materials. Asbestos fibres are considered to be highly
3.3.2 Conversions                                               carcinogenic and are released in particular during
                                                                demolition work.
In the planning a high-rise building, care is normally taken    The technical equipment in the building, such as heating,
to ensure that the building can subsequently be used in a       sanitation or elevators, must also be rehabilitated after a
relatively flexible manner. Internal conversions due to         certain period of time. In many cases, however, such re-
changes of use following a change of tenant or the chang-       newal or modernization work is undertaken without shut-
ing needs of the present user should not be a problem. In       ting down the entire building. It is often sufficient to shut
this way, the operator of the building can also respond         down only part of the building, and sometimes the work
more effectively to changes in the property market.             can even be carried out without interrupting operation of
To ensure such flexibility, the service systems are centrally   the building at all.
located in the building. The partition walls separating the
individual rooms are non-supporting and can be relocated
to permit subsequent changes in room size. As a rule, the
building’s supporting structure is totally isolated from the
system of partition walls inside the building. Where pos-
sible, reinforcing walls are located outside the useful floor
area, such as in the core area. The columns are conse-
quently the only remaining load-bearing elements causing
a “nuisance” in the useful area. A column spacing of 6 to
7 m is widely used as a standard grid, meeting both archi-
tectural and structural requirements.
If the conversion nevertheless affects the load-bearing
structure of the high-rise building, it is essential to draw
up a structural analysis for all building states during the
conversion work in order to avoid damage. If other parts
of the building remain in use during the conversion work,
3 Technology of high-rise construction                                                                                    Page 54

3.4 High-rise construction in the future

In view of the anticipated population explosion and
the concentration of dwellers in the conurbations,
the need for high-rise buildings will continue to grow,
especially with building land becoming increasingly
scarce and property prices soaring as a consequence.
The Australian Embassy in Tokyo sold 500 m2 of its
garden in return for DM 1.25m – per square metre!
Such astronomical prices can be more easily
understood if we consider that there are currently
5,400 people per square kilometre in Tokyo and
that the population in this conurbation is forecast
to increase from 18.5 million at present to almost
30 million in the coming decades. In some regions,
it will only be possible to settle new residents or busi-
nesses if they can be accommodated in high-rise

It is already certain that today’s (1999) world record for the   height. It does not take a prophet to forecast that the
tallest building – the twin Petronas Towers in Kuala Lum-        future of high-rise buildings – these “architectural dino-
pur (452 m) – will not be held for long. A new record-           saurs”, as one critic recently wrote – is highly uncertain in
breaking edifice, the Chongqing Tower, is already under          their traditional form. The disproportionately large manu-
construction in Shanghai. Specific plans have already            facturing effort, the high operating costs due above all to
been drawn up for an 800-m-high building in Tokyo (Mil-          the excessive consumption of energy, and reservations as
lennium Tower), and totally inconceivable, gigantic pro-         regards health and safety will result in a new kind of high-
jects involving heights of several kilometres are also under     rise building totally different from today’s.
discussion. One of the most unusual is the Japanese pro-         Since technological progress is advancing steadily, how-
ject TRY 2004, a pyramid rising 2004 m into the sky. It is       ever, and the attitudes of both owners and architects will
to be made up of 204 octahedral elements which can be            also be of decisive importance, one would almost require
mutually sealed off from one another if a fire breaks out.       the skills of a clairvoyant to predict with any accuracy the
In this way, living space is to be created for one million       specific changes which are impending. Nevertheless, we
people over an area of 8 km2.                                    shall at least venture a rough prediction of possible future
Economic considerations could impose limits on these gi-         developments.
gantic plans, for the costs for construction and operation
of a high-rise building increase exponentially with its

                                                                                                                41 PETRONAS TOWER
3 Technology of high-rise construction                                                                           Page 56

             259 m                       296 m            310 m           381 m                       381 m

                                                                                            42 TREND TOWARDS EVER-TALLER
                                                                                               MODERN HIGH-RISE BUILDINGS
Page 57                                                      3 Technology of high-rise construction

431 m        443 m         452 m             457 m (under construc-           800 m (planned)
(2624 feet)

43 THE MILLENNIUM TOWER – a vision for the 3rd millennium
(1482 feet)


 (1453 feet)

(1250 feet)

(850 feet)
3 Technology of high-rise construction                                                                                       Page 68

ENERGY SAVINGS                                                  POWER GENERATION
Consistent use of the savings potential already available       High-rise buildings are positively ideal for generating
today will indisputably be the most important “source” of       power: the huge facades are usually exposed to the sun
energy in the future. Numerous studies have proved that         from dawn to dusk and the prevailing winds on the roof
energy savings of up to 80% can be realized in both the         are considerably stronger and more persistent than those
private and the commercial sector without any loss of           on the ground. And these are also the main sources of en-
comfort or convenience. “Intelligent energy consumption”        ergy to be used in the future: wind-operated plants to gen-
is a term that is increasingly being used in this context. As   erate electricity on the roof or particularly exposed edges
a result, the foundations for a building’s future consump-      of the facade, collectors to heat air or water and photovol-
tion of energy are already set in the planning stage: the       taic systems to generate electricity on the facades and
topographical surroundings are of importance here, as is        possibly also for producing hydrogen at a later stage.
consideration of the prevailing wind strengths and direc-       Generation of heat via the deep-pile foundations asso-
tions, and any shadows cast. An energy-efficient building       ciated with virtually every high-rise building is a less ob-
will be positioned with its “broadside” away from the sun       vious possibility. When the building is complete, water
in warmer climates, while every effort will be made to          can be circulated through heat exchanger tubes integrated
ensure that as much of the facade as possible faces the         into the pile reinforcements. Due to the feed and return
sun in colder climates. Windows facing the sun should be        flow of the water, the different energy potential between
as large as possible, those facing way from the sun as          footing and building can be exploited and the subsoil
small as possible (the keyword is: passive solar architec-      used as a seasonal or temporary store of energy. One
ture). A rotary building is another conceivable possibility     of the first projects of this type has already been realized
and could be turned towards or away from the sun as re-         in the rebuilding of the Commerzbank headquarters
quired. Particular attention must be paid to thermal insula-    in Frankfurt am Main.
tion of the facade. Northern European construction stand-
ards are a positive example here, as they specify a thick-      CONSTRUCTION BIOLOGY
ness of several decimetres for the insulating layers. Trans-    The more we know and learn about the harmful effects of
parent thermal insulation will probably become estab-           modern materials and installations on health, the less
lished in future, as it not only reduces the heat loss, but     probable it becomes that future generations will voluntar-
can also attract additional heat by allowing the radiated       ily accept this hazard. Research and industry must there-
heat to reach the facade without obstruction. Thermopane        fore find acceptable alternatives, such as emission-free
glazing with a k-value of less than 1 already represents the    materials, installations, insulating and isolating materials,
state of the art today, as does solar glazing with almost       adhesives and coatings, as well as avoiding the use of
100% reflection of the radiated heat.                           chemicals which give off toxic gases in the event of a fire.
Considerable savings can also be achieved inside the
building, for instance by using a combined heat and
power generating unit instead of conventional heat and
power generation, or by using variable-speed forced-circu-
lation pumps in the sanitation, heating and air-condition-
ing sectors, or by using energy-efficient fluorescent tubes
which require up to 80% less electricity than conventional
filament lamps, or by controlling the lights via movement
detectors and naturally by ensuring the energy efficiency
of every single appliance used in flats or offices, from
well insulated fridges to personal computers with low
power consumption. Reusing the off-heat from air and
water will be a matter of greater importance in the future.
Ideally, our future energy requirements should all be met
by regenerative sources.

                                                                                   48 ADDITIONAL HEAT RECOVERY VIA PILING FOUNDATIONS
                                                                                               IN THE COMMERZBANK HIGH-RISE BUILDING
3 Technology of high-rise construction                                                                                  Page 70

The construction of high-rise buildings will be dominated by four factors in future, namely: time savings, personnel
savings and financial savings, in addition to the energy savings already mentioned above.
As examples in Japan show, it is already possible to erect buildings with the help of assembly robots. The required ele-
ments are designed and drawn with the aid of computers (CAD = computer-aided design). The computer automatically
retrieves all the required (dimensional and design) data from the saved architectural and engineering drafts, as well as
from detailed libraries. The parts are then manufactured by fully automatic machines on the basis of these production
data (CAM = computer-aided manufacture) and transported to the site “just in time“. Assembly robots pick out the right
part in the right sequence, transport it to the assembly point and install the finished element in the right place.

Thanks to the efficiency of the computers and robots,
buildings erected in this way bear little resemblance
to the conventional edifices erected with prefabricated
parts: the precision and arithmetic accuracy of these
machines permits a hitherto inconceivable variety of
forms and even the most complex structural analyses
are mastered with the help of computers.
If the engineers who developed and built these robot-controlled “construction machines” are to be believed, then this
method can not only considerably cut the time required for construction work, but can also reduce the construction costs
by up to 40% and reduce the workforce required for conventional construction projects by up to one-third (roughly one-
half of these would then find work in the component manufacturing plants). Above all, the dangerous and physically
strenuous work would be eliminated.
In this way, something that was considered Utopian only a few years ago has already begun to become an everyday real-
ity: huge edifices and even complete towns are erected by robots as if guided by a ghostly hand. In spite of this, how-
ever – or perhaps for precisely this reason – highly qualified experts will be needed to develop, operate and control the
necessary computer programs, techniques and technologies.

                                                                                                49 FULLY AUTOMATED BUILDING SITE
        52 NEW YORK
              Page 78

Page 79
4 Risk potential

4.1 Design errors
4.2 Fire
                    4.3 Windstorm   4.5 Foundations, settlement 4.7 Special structural measures 4.9 Loss of profit
                    4.4 Earthquakes 4.6 Water                   4.8 Other risks
Page 85                                                                                                        4 Risk potential

The following sections consider all of the hazards
constituting the greatest risk potential during the
construction and occupancy of a high-rise building.
The commentaries will be illustrated by examples of
losses and rounded off by proposals which need to
be implemented to minimize such risk potential and
prevent losses.

4   Risk potential

4.1 Design errors                                              Such aspects include compliance with fire protection re-
                                                               quirements in the building, the position and number of
Fortunately, no-one really knows just how many rumoured        escape routes and the number, location and execution of
design errors by architects are actually true. They are said   stairwells and traffic areas. Even such seemingly less im-
to have forgotten not only the toilets, but even complete      portant aspects as compliance with accident prevention
stairwells in multi-storey buildings. And today’s construc-    regulations are reviewed, for instance as regards the
tion practice makes such design errors more probable than      height of railings or the distance between bars in railings
ever: since the supporting structure, shell and core, and      and grids.
interior finishing are totally isolated from one another not   In many cases, however, the design is changed at short
only during the design phase, but also during the subse-       notice during the construction phase, with the result that
quent construction phase, errors may possibly not be dis-      the plans submitted for inspection no longer reflect the
covered until the work has reached a fairly advanced stage.    actual situation. If errors are made by the designer at this
This leads to time-consuming and costly changes and cor-       stage in violation of building and planning codes, they will
rections, usually at the expense of the professional indem-    only be discovered (if at all) during final inspection of the
nity insurance prescribed for architects in many countries.    building by the construction supervisory authority as
The most commonly occurring design errors can be sub-          specified in many countries.
divided into two groups: failure to observe building and       Such changes frequently cannot be undone, and this
planning codes on the one hand, and errors in the choice       forces both sides to accept compromises possibly at the
of materials and wrong or inadequate construction details      expense of the building’s safety. Despite the numerous
on the other.                                                  statutory instruments and court rulings in test cases, the
                                                               complex legal relationship between principal and architect
FAILURE TO OBSERVE BUILDING AND PLANNING CODES                 makes it necessary for the courts to decide who is to bear
It may be assumed that, in the majority of countries, when     the costs incurred as a result of such errors. In most cases,
a building exceeds a certain size – and this will certainly    both the architect’s legal protection insurer and his profes-
apply to high-rise buildings – corresponding plans must        sional indemnity insurer will be involved.
be submitted to the construction licensing and supervisory     If the errors are not discovered and the building is taken
authorities for inspection. The inspection and approval        into service, however, this may not only increase the prob-
procedure not only encompasses aspects under the build-        ability of a loss occurring, but also pose an acute risk to
ing code, such as compliance with specified distances and      life and limb for its users. Particularly grave defects only
the specified height and size of a building or its type of     become evident when the loss actually occurs, for in-
use, but also the safety of the people inside the building.    stance when a fire occurs. Fire insurers, personal accident,
4 Risk potential                                                                                                       Page 86

health and life insurers, occupational disability insurers       can be sure of having underwritten a completely new risk.
and once again the liability insurers may all be called          As already mentioned in Sections 3.2.3 and 3.2.4, the con-
upon to bear the costs once the courts have settled the          struction of modern office towers has little in common
question of blame. If a guilty party can be identified, that     with the construction methods employed in the past. In-
party can face considerable penalties for any shortcom-          stead of solid ceilings and walls, we now have a skeleton
ings ascertained. It is irrelevant in this context whether       structure – usually made of steel – with endless kilometres
this party was actually aware of these shortcomings or           of wiring for telecommunications, switching, control and
merely must have been aware of them.                             air-conditioning running vertically and horizontally
For this reason, all insurers – and particularly fire insurers   through the entire structure. During both the construction
– are well advised to ascertain whether all of the safety re-    and the operating phases, this combination consequently
quirements have been met before they conclude a policy           poses an enormous risk for the spread of fire and smoke,
for buildings entailing high risk potential.                     as well as for the harmful effects of heat, fumes and water.

Not only the legal relationship between principal and            This new 12-storey office tower is one of fourteen build-
architect is exceedingly complex; just as complicated is         ings erected over the railway tracks of a station in the City
that between architect and (sub)contractors and particular-      of London. Due to the extremely confined conditions, the
ly among the (sub)contractors themselves.                        containers accommodating the construction workers were
Although the architect or specialist engineer specifies          installed on the first floor of the shell.
which materials are to be used or installed, the (sub)con-       During the evening of 22nd June 1990, an electrical appli-
tractor must check whether these materials are indeed            ance or short-circuit caused a smouldering fire in one of
suitable for such use. Modern and unconventional con-            these containers. Undiscovered for several hours, this
struction practices frequently make it difficult or even im-     smouldering fire charred the interior furnishings until it
possible for (sub)contractors to determine whether the           reached the polystyrene foam inside the steel walls of the
specified materials or the execution intended by the             container. This resulted in major generation of smoke until
designer are indeed suitable and correct.                        the container literally burst apart around midnight and
Unsuitable materials and connections in sanitary installa-       caused a major fire.
tions, for instance, can rapidly result in water damage due      The fire was only discovered by a security patrol roughly
to burst pipes.                                                  30 minutes later after a smoke detector was tripped. When
Unsuitable insulating materials can give off toxic gases or      the fire brigade arrived another seven minutes later, the
acids in the event of a fire; incorrectly dimensioned fix-       temperature around the container was apparently already
tures for suspended ceilings or facade elements can cause        in excess of 1,100 °C. Twenty fire-fighting teams with over
bodily injury or property damage if they fall down.              100 firemen fought for almost five hours to bring this diffi-
In extremely simplified terms, it could be said that most of     cult fire under control.
the damage incurred in or on a building is ultimately at-        The extreme heat ultimately caused the steel skeleton and
tributable to design errors.                                     a number of ceilings to fail. A large area in the middle part
                                                                 of the roughly 40-m-high building subsequently dropped
                                                                 by between 0.6 and 1.2 m. The fire also destroyed material
                                                                 which was stored on the first and second floors. This led
4.2 Fire                                                         to even more intense smoke emission, which in turn
                                                                 caused extensive damage to the aluminium facade and
Fire is one of the greatest risks for every building and par-    valuable interior fittings.
ticularly for high-rise buildings. Due to the spectacular        The considerable property damage worth around £36m
photographs and film sequences shown in the media,               was the highest fire loss to have been incurred in a high-
major fires have always made – and will continue to              rise building in the United Kingdom up to that time and
make – headline news not only during the construction            was due to the absence of an early-warning system, the
phase, but above all during the occupancy phase. They            widespread propagation of fumes due to the chimney ef-
are a major headache to all insurers and reinsurers due          fect of the atrium and the presence of numerous openings
in particular to the exorbitant rise in repair and restoration   in walls and ceilings. Moreover, neither the fire-alarm
costs, as well as the loss of human life.                        system nor the risers and sprinkler system had been acti-
A few examples of major fires during the construction and        vated in this stage of the building’s construction.
occupancy phases are provided below.
                                                                 LONDON UNDERWRITING CENTRE
4.2.1 Examples of losses during the construction phase           A fire broke out during the interior finishing work in this
                                                                 over 55-m-high office tower in London’s banking and in-
GENERAL                                                          surance centre in August 1991. The cost of repairing the
It is not always easy for an insurer to determine which          damage consumed £110m or around 75% of the insured
risks may be associated with technical improvements, new         value of the building and was far higher than the cost of
techniques, new materials or combinations of different           repairing the damage following the Broadgate fire in the
materials. It is only when the loss occurs that the insurer      previous year. First estimates indicated that the loss would
57 FIRE IN THE BROADGATE BUILDING, LONDON: sunken roof support beams

Page 89                                                                                                           4 Risk potential

be no more than a fraction of the final cost, and to the         smoke. Three men died in the fire or as a result of jump-
man on the street the building appeared to have survived         ing out of a window.
largely unscathed, at least from the outside, and merely         Altogether, 40 fire brigades with over 2,000 firemen fought
had to be cleaned.                                               for roughly six hours to bring the fire under control. Their
The fire broke out on the ground floor at the beginning of       work was impeded from the very beginning by the narrow
the morning shift, near the atrium where it was extensive-       access roads. The water pressure from their nozzles only
ly nourished by the considerable material and packaging          reached up to the 10th floor.
scrap which had been stored there. Although the fire bri-        Subsequent investigations revealed that although all the
gade arrived within minutes despite the early morning            fire-prevention requirements, such as smoke detectors,
rush-hour and narrow streets, it proved extremely difficult      fire walls, firemen’s lifts and sprinkler systems, had been
to bring the fire under control. Thanks to the atrium, the       met, these systems had not been activated during the con-
flames had already reached the roof and were reaching            struction phase. It is assumed that the fire was most prob-
out towards the unsealed floors leading off to the sides.        ably caused by a bucket of thinners igniting on contact
The atrium itself was difficult to reach since it was com-       with sparks from welding work being done on parts of the
pletely encased in scaffolding for installation of 16 large      air-conditioning system.
escalators. The stairwells were almost impassable on ac-         Despite the extensive damage, the hotel – which is located
count of the immense heat and smoke. It was only when            on the 17th to 36th floors of the building – was opened
the roof above the atrium broke and the smoke was dis-           without undue delay. In the department store, around
pelled that the firemen were able to make progress in            3,000 m2 out of more than 130,000 m2 was seriously
bringing the fire under control.                                 damaged by the fire, but the supporting structures re-
The considerable increases in the cost of repairing the          mained unscathed. Completion of the store is expected to
building during the ensuing months were due almost ex-           be delayed by several months. The total loss is estimated
clusively to the extreme spread of harmful fumes. These          to be in the region of DM 25m.
fumes (including chloride-laden fumes from burning PVC
cable installations) had spread through openings in walls        4.2.2 Fire protection on construction sites
and ceilings, as well as the false floors, to all floors above
and below ground and had settled on most of the installa-        Numerous similar major fires in the recent past have clear-
tions and facade elements. Further damage was caused by          ly shown that too little attention is still being paid to fire
contaminated fire-fighting water in the false floors and         prevention on construction sites for buildings in general
basement floors. The supporting structure, on the other          and for high-rise buildings in particular. This has led to
hand, suffered very little damage.                               devastating fires and immense costs for the insurance in-
In addition to requiring extensive decontamination, such         dustry.
fires also raise questions with regard to warranties. Sup-       These fires are more likely to be caused by human negli-
pliers may have guaranteed the serviceability and appear-        gence than by technical defects, for example workers care-
ance of their parts and installations over a period of sev-      lessly throwing away glowing cigarette ends and the im-
eral years, but no-one can judge how the frequently com-         proper use of cooking appliances in the workers’ quarters,
plex switchgear, for example, will respond over the years        which are frequently located in the shell of the building.
to the extreme heat and corrosive fumes produced by the          Moreover, as the fires in the Broadgate Building (1990)
fire. In addition, the commonly used PVC sheathing also          and the London Underwriting Centre (1991) clearly
produces highly corrosive substances.                            showed, an atrium in the building can have extremely
                                                                 negative effects in the event of a fire, as its considerable
MERIDIEN PRESIDENT TOWER                                         area positively invites misuse as a place for storing large
This 36-storey hotel and shopping centre in Bangkok was          quantities of material, particularly during the construction
almost complete and about to be inaugurated when a fire          work. These materials are easily combustible on account
broke out following an explosion during installation of          of their packaging, which is usually not removed before-
parts of the air-conditioning. The fire very rapidly spread      hand and therefore constitutes an increased fire risk. In
through the air-conditioning shafts and soon reached the         addition, the chimney effect (i.e. vertical draft) due to the
10th floor, as well as lower floors.                             atrium helps the fire to spread rapidly to the roof and
When the fire broke out, more than 150 construction work-        other floors leading off from the atrium.
ers were adding the finishing touches to the inside of the       The situation is further aggravated by the fact that, even if
building. Since the workers on the upper floors were un-         the risk potential is acknowledged, safety features are the
able to make their way downwards, roughly 40 fled onto           first to be sacrificed under the rising pressure of time and
the roof while others used ropes to lower themselves onto        costs. The growing use of combustible materials, the high-
a veranda on the 5th floor so that they could escape from        er fire load and its distribution over all floors are therefore
the flames.                                                      the main reasons for catastrophic major fires.
Despite the intense smoke, seven helicopters succeeded in        This trend has become unacceptable in the United King-
rescuing the men on the roof, as well as another 50 from         dom. In an unrivalled campaign, fire brigades, insurance
lower floors with the aid of ladders and straps. One of the      companies and the construction industry have drawn up a
helicopters was even forced to make an emergency land-           “Joint Code of Practice” for fire protection on construction
ing after its tail rotor touched the building in the dense       sites. Compliance with the regulations and requirements
4 Risk potential                                                                     Page 94

Page 95   4 Risk potential
Page 99                                                                                                             4 Risk potential

contained in this Code has now become an indispensable           4.2.3 Examples of losses during the occupancy phase
element in the terms of insurance for the construction of
major high-rise projects. This Code specifies in detail how      GARLEY BUILDING IN HONG KONG
fire protection is to be effectively organized and imple-        “Elevator to hell”, “Trapped in a burning skyscraper”,
mented in all the various areas and phases of construc-          “Towering inferno” – these are just a few of the headlines
tion.                                                            in world press reports on one of the most devastating fires
Adequate protection against fires can only be guaranteed         in Hong Kong in almost 40 years.
by clear instructions and standards which are implement-         During welding work in an elevator shaft in the 16-storey
ed from the very beginning of the construction work and          Garley Building in Hong Kong’s Kowloon district on 21st
which are regularly monitored and supported with corres-         November 1996, a fire broke out which killed 39 people
ponding investments in time, money and material.                 and seriously injured around 80 others. More than 90
Particularly in the case of high-rise construction, prevent-     people were rescued, some of them in daring scenes in
ive fire protection must be included from the planning           which a helicopter pilot risked his own life.
phase onwards so that the various construction phases            Maintenance and repair work was in progress in the office
can be taken into account accordingly. One of the essential      and business tower when highly flammable material
conditions for effective fire protection is the appointment      caught fire during welding work in the basement. The fire
of a safety officer responsible for risk management on site.     made its way up through the elevator shafts and spread
A whole team of safety officers may be appointed for a           like lightning through the top three floors of the building.
high-rise construction site; in such cases, they are often re-   The immense heat and smoke made these floors a death
sponsible for personal and occupational safety, as well as       trap for the people working there: the windows could not
for fire protection. In addition to drawing up, implement-       be opened to let the heat and smoke out, and escape
ing and verifying the fire-protection concept, it is import-     routes were filled with smoke or impassable on account of
ant to train the site personnel in fire-fighting techniques      the fire. As a result, 22 charred bodies were subsequently
and to familiarize the fire brigade with the site.               found in a single office on the 15th floor.
Since the situation on site is subject to constant change in     The fire brigade was called shortly after the fire broke out
line with the progress made during the various construc-         and arrived on the scene shortly afterwards, so that many
tion phases, the site drawings must be regularly updated         of the people in the building were fortunately saved. Al-
with regard to access roads for the fire brigade, fire com-      though hundreds of firemen were at the scene of the fire,
partments, water supply lines and fire loads in particularly     it took over 20 hours to bring the fire under control.
high concentrations. Such risks as combustible liquids,          What were the reasons for the fire being able to spread so
gas depots, cable ducts and temporary openings in walls          rapidly, for the magnitude of the loss and the numerous
and ceilings must be highlighted in the same way as the          fatalities? The primary cause lay in the totally inadequate
available fire-fighting equipment.                               fire-protection installations in the 21-year-old Garley Build-
Above all, particular attention must be paid to preventive       ing. There was neither an automatic fire alarm nor a
fire protection. The primary objective must be to reduce         sprinkler system. From the speed at which the fire spread
the fire load. Waste materials must be removed regularly         through the elevator shaft to the upper office floors, it may
and combustible waste collected from the individual floors       be assumed that the structural fire protection was also in-
every day. The value of material stored for construction         adequate. It is claimed that plywood had been used as
and assembly work should be limited, the material spread         provisional elevator doors.
over several storage units and protected by special meas-        The Hong Kong Fire Prevention Act stipulates that all high-
ures, such as fire walls or sufficient distance, in order to     rise buildings licensed after 1973 must be equipped with a
reduce what is frequently a very high fire load.                 sprinkler system, among other things, but this did not
Specific control of all work constituting a fire hazard is an-   apply to the Garley Building. In view of the large number
other essential precaution. A special approval procedure is      of older buildings in a similar condition to that of the Gar-
being introduced to ensure safer practices with grinding,        ley Building, the headline in one Hong Kong newspaper –
cutting or welding work, for example, as well as work with       “700 office buildings could become death traps” – is not
soldering lamps, application of hot asphalt or other work        so far-fetched.
with radiant heat. At least one person trained in fire-fight-
ing techniques and equipped with a fire extinguisher must        FIRST INTERSTATE BANK BUILDING IN LOS ANGELES, USA
always be present during such work. Even when the work           Once the tallest building in California, the 261-m-high,
is complete, however, the area must be inspected again to        62-storey office tower fell prey to what is considered to
ensure that a fire cannot break out subsequently (e.g. as a      have been one of the most destructive skyscraper fires in
result of glowing welding slag).                                 the USA in recent years when, for reasons unknown, a fire
The site should be fenced off and access controlled in           broke out on the 12th floor on the evening of 4th May
order to minimize the risk of fires due to third parties.        1988. From the fire-fighting point of view, it represented
                                                                 one of the biggest challenges for the Los Angeles City Fire
                                                                 Department. With 383 firemen, almost one-half of the en-
                                                                 tire shift on duty in the city was called out to fight this fire.
                                                                 The fire was brought under control after 31/2 hours. The
                                                                 12th to 16th floors were gutted. The floors above suffered

4 Risk potential                                                                                                      Page 104

considerable damage due to smoke and those below were          be abandoned on account of the major smoke in the stair-
extensively damaged by fire-fighting water.                    wells with their chimney effect.
One maintenance technician died when he took the eleva-        Broken glass panes on the facade posed another problem
tor to the floor in which the fire had broken out because      as they fell down onto firemen and fire engines feeding
an open fire door had evidently jammed between the             water into the fire connections at the foot of the building.
burning office area and the lobby in front of the elevator.    Cut hoses had to be replaced more than once. The glass
Around 50 people were injured, including several firemen.      panes also came down in large units, as they were bonded
The loss totalled more than US$ 50m, plus losses amount-       together by the reflecting plastic coating; even the coating
ing to tens of millions for business interruption.             was burning in some cases.
The building had been completed in 1973 before the             As a precautionary measure, the newly installed sprinkler
sprinkler regulation for high-rise buildings in Los Angeles    groups on floors 17 to 19 above the burning floors were
came into force. This regulation stipulates that sprinklers    also activated so that they would have provided effective
must be installed throughout the building. At the time of      assistance had the fire spread above the 16th floor, but
the fire, work was under way to install a sprinkler system     this proved unnecessary.
in the rest of the building to ensure better fire protection   The defects and negative factors will be discussed in more
for the roughly 4,000 employees and tenants in the build-      detail in the next section. The positive factors in this diffi-
ing and to supplement the sprinkler system which was           cult fight against a fire are summarized here:
originally only installed on the lower level of the under-     – Concentrated and well organized deployment of
ground car park. Work on the new sprinkler system was al-        firemen.
ready 90% completed at the time of the fire, even in the       – Resistant supporting steel framework thanks to the fire-
floors affected by it, but the system had not yet been taken     resistant spray-coating.
into service. Parts of the riser had also been drained and     – Sophisticated emergency plans by the bank made it
fire pumps switched off in the building.                         possible to continue bank operation without a hitch in
The fire brigade was alerted by a neighbour, as there was        an emergency centre on the morning following the fire
a delay before the alarm warned security personnel des-          and throughout the months of cleaning and repair work
pite the fact that the automatic fire-detection system was       in the building.
functioning correctly; this delay was due to human error       – As a result of this fire, a regulation was issued specify-
and incorrect regulations. As a result, the security person-     ing that sprinkler systems had to be retrofitted in all
nel disregarded a fire alarm triggered manually by the in-       450 high-rise buildings without such sprinkler protection
stallation workers in response to minor smoke emissions,         in Los Angeles within a transition period of three years.
as well as other alarms by smoke detectors on the 12th
floor.                                                         ONE MERIDIAN PLAZA IN PHILADELPHIA, USA
By the time the fire brigade arrived, most of the 12th floor   On the evening of 23rd February 1991, a fire broke out on
was already in flames. Since use of the elevators was pro-     the 21st floor of this office tower with 38 floors above
hibited by regulations, the firemen had to carry their         ground and three underground floors. Three firemen were
heavy equipment up the stairs to the scene of the fire.        killed in action and 24 others injured.
As a result, roughly half an hour passed before they were      There were only a few people in the building when an
actually able to start fighting the fire with water from the   automatic fire-detection system on the 21st floor triggered
risers in the four stairwells.                                 an alarm on the central control panel on the ground floor
Fighting the fire proved to be a difficult matter. Once        at 20.23 hours. The fire brigade was called by neighbours
again, the excessively low water pressure had to be boost-     before an alarm could be sent from there to the fire bri-
ed with the aid of fire pumps and additional water sup-        gade.
plied via the risers. Since the fire doors leading to the      The first firemen arrived on the scene after seven minutes
stairs had been opened, smoke and fumes soon spread            and took the elevator up to the 10th floor. From there, they
upwards.                                                       took the stairs up to the burning floor. Since the power
In the meantime, the fire had spread to floors above the       supply, including the emergency power supply, failed in
12th floor with flames up to 10 m high leaping from            the entire building shortly afterwards, the firemen had to
broken windows on the outer facade. Fire and smoke also        carry all their equipment up the stairs, thus considerably
penetrated through incompletely sealed cable openings          delaying the commencement of their fire-fighting efforts.
and air-conditioning ducts, as well as through the 31 ele-     Licensed in 1969 and completed in 1972, the building was
vator shafts.                                                  only equipped with sprinklers in a few areas of the under-
In addition to the intense heat and smoke in the stairwells,   ground floors. In 1988, the building’s owner decided suc-
the firemen’s work was further impeded by failure of the       cessively to install sprinklers throughout the whole build-
power supply and of the emergency lighting in the stair-       ing. Only a few floors from the 29th upwards had been
wells. The vital radio link was similarly impeded by the       equipped with sprinklers when the fire broke out.
shielding effect of the building’s steel skeleton and the      Originally dry risers had been converted into wet risers to
large number of firemen on the scene.                          supply the sprinklers during the installation work. Two
Helicopters were called in to drop firemen onto the roof of    sprinkler pumps were similarly installed, as were pressure-
the building to allow them to head down towards the seat       reducing valves on the connections for the wall hydrants
of the fire via the stairwells. However, this attempt had to   installed on all floors. Following the fire, it was found that
Page 105                                                                                                         4 Risk potential

these valves had been wrongly set so that the water pres-         CONCLUSIONS
sure from the wall hydrants was too low.                          These fire catastrophes have once again shown that the
This also explains why the firemen’s efforts proved unsuc-        threat posed by fires in high-rise buildings still exists.
cessful – the fire on the 21st floor had turned into a conflag-   Although in some cases exceedingly more stringent regu-
ration in the meantime. Due to the excessively low water          lations and fire-protection requirements were introduced
pressure, both the volume of fire-fighting water and the          for high-rise buildings in many countries throughout the
range were inadequate. After four hours, the sprinkler in-        world in the 1960s and 70s after a series of devastating
staller succeeded in adjusting the pressure-reducing              fires in various countries with in some cases numerous
valves with the aid of special tools so that the required         fatalities (Brazil, Colombia, Venezuela, Korea and others),
water supply could be guaranteed.                                 there are still a large number of older high-rise buildings
In the meantime, the fire had spread to three other floors        which do not come under the more stringent regulations
and the stairwells were filled with smoke. The fire spread        or at least not fully – as the fire in Hong Kong proves –
particularly along the outer facade. Three firemen died as        since separate statutory rules and regulations are required
they tried to clear the smoke in one of the stairwells by         to retrofit structural changes and fire-protection equip-
smashing windows.                                                 ment in existing buildings.
After roughly 11 hours fighting the fire, the firemen had to      The following list of negative features can be drawn up on
retreat from the burning floors because the ceilings threat-      the basis of these fires during the occupancy phase, more
ened to collapse. It was therefore decided to fight the fire      or less representative of numerous similar occurrences in
via the sprinkler system already installed on the 29th floor.     high-rise buildings:
The required water pressure was to be obtained by feed-           – absence of fire compartments on large open-floor areas;
ing water into the risers. Ten sprinkler heads were acti-         – vertical spread of fire and smoke through stairwells and
vated by the heat of the fire and it was finally brought             air-conditioning ducts not sealed by fire dampers (chim-
under control around 15.00 hours on 24th February.                   ney effect);
Altogether 19 hours were needed to put the fire out com-          – lack of sealing on cable ducts in stairwell walls;
pletely. It is assumed that the fire was caused by spon-          – inadequate evacuation of people due to smoke-filled
taneous ignition of oil-soaked rags. In addition to total            stairwells;
destruction of the entire furnishings on the floors affected      – impeded access to the actual seat of the fire;
by the fire, the building’s structure and outer facade also       – absence of a suitably protected firemen’s lift with separ-
suffered considerable damage.                                        ate power supply in high-rise buildings with more than
The owner of the building demanded over US$ 250m in-                 30 floors;
demnification from the insurers for the repair costs and          – threat of ceilings collapsing on account of inadequate
other losses. In his view, the steel structure of the upper          resistance to fire;
floors from the 19th floor upwards had been so severely           – failure of the emergency power supply since it was not
damaged by the heat that the only alternative was to de-             isolated from the shaft of the main power supply;
molish and subsequently rebuild the tower. An expert ap-          – no continuous, automatic fire-detection system to give
pointed by the courts, however, agreed with the insurers             early warning of a fire, to signal a fire and to permit
that the building could be repaired without demolishing it.          rapid location of the fire;
After protracted negotiations, the claim was settled six          – inadequate instruction and training of security person-
years after the fire. The building had neither been repaired         nel regarding the action to be taken in the event of an
nor was it partly occupied at that time. Barely a year later         alarm and fire;
it was demolished, probably on account of the significant         – lack of standardized procedures between the alarm
deterioration in its condition and on account of its contam-         regulations and the guidelines published by the fire
ination with asbestos and PCB (polychlorinated biphenyls).           brigade;
The robust roof and facade construction considerably im-          – inadequate supply of fire-fighting water due to exces-
peded the demolition work. The building’s location in the            sively low pressure in the risers, often on account of a
city centre and adjacent buildings, as well as underground           partly closed shutoff valve or incorrectly set pressure-
rapid-transit railways under the building, prohibited the            reducing valves;
use of explosives. The demolition costs were estimated at         – external attempts to boost the water pressure thwarted
US$ 25m over a period of two years.                                  by inappropriate marking of the fire connections;
                                                                  – no automatic fire-fighting systems, such as sprinklers;
                                                                  – failure of the sprinkler systems installed to function

                                                                                 69 FIRE-DETECTION SYSTEM IN THE MESSETURM IN FRANKFURT
Page 107                                                                                                         4 Risk potential

4.2.4 Fire-protection regulations, loss prevention               The German directives specify a fire-resistance period of
                                                                 90 minutes for the supporting structure in high-rise build-
The facts and shortcomings outlined in the preceding sec-        ings and 120 minutes for buildings with a height of more
tion have significantly increased the magnitude of the fire      than 60 m. In both cases, only non-combustible materials
losses described.                                                may be used for the supporting elements.
For this reason, efforts are being made to limit the fire risk   Since high-rise buildings are largely constructed with steel
with the aid of corresponding fire-protection regulations        skeletons, unprotected steel cannot be used on account of
and loss-prevention measures.                                    its inadequate resistance to fire. Composite structures of
A high-rise building does not constitute any extra risk with     concrete and steel or fire-resistant coatings or fire-proof
regard to occurrence of the fire, but it certainly does with     panelling must be used instead.
regard to the spread of fire, smoke and fumes. This is due       So that the building itself cannot contribute towards the
to the vertical nature of the building, which greatly pro-       spread of fire, non-combustible materials are largely stipu-
motes the spread of fire in the main propagation direction,      lated for the structural parts and elements. Combustible,
namely from the bottom upwards.                                  normally or barely flammable materials are only permitted
Compared with buildings below the limit for a high-rise          if structural measures ensure that they cannot contribute
building – regardless of definition – a high-rise building       towards a fire.
will always have significant disadvantages when it comes
to rescuing people and fighting fires. People cannot be          FIRE COMPARTMENTS
rescued from outside the building if they are trapped on         As already mentioned, fire can also spread via the outer
floors out of range of the fire ladders; they can only be lo-    facade if windows have been shattered by the heat. It has
cated and rescued via the stairwells. The same applies to        been found in such cases that the flashover distance of at
fighting the fire, since outside intervention is impossible.     least 1 m between two floors as required by the directives
The firemen must concentrate on tackling the fire from in-       is frequently too short. The alternative possibility of parts
side the building and must make their way to the scene of        projecting from the facade is similarly not always effect-
the fire with their equipment through stairwells filled with     ive, and it is therefore perfectly appropriate to use fire-
smoke and heat.                                                  resistant glazing.
                                                                 In the cases described above, it was sometimes found that Regulations                                              the fire had spread over the entire floor and also over sev-
                                                                 eral floors inside the building. Fire compartments with
Due to these difficulties, the standards and regulations in      vertical and horizontal structural seals must be created to
force in the majority of countries include special provi-        prevent fire spreading in this way:
sions for high-rise buildings, with corresponding require-       – The ceilings must be fire resistant and made of non-
ments to be met in respect of fire prevention and protec-           combustible materials.
tion. In this way, they take account of the higher risk po-      – Partition walls must be made of non-combustible ma-
tential.                                                            terials and must also be fire resistant for certain uses.
In Germany, for instance, these requirements are laid out        – Doorways should at least be sealed with tightly closing,
in the 1978 “directives”. Besides, compliance with all the          fire-retardant doors; any other openings required in the
provisions of the Construction Codes in force in each fed-          walls must be sealed in an equivalent manner.
eral state is compulsory.                                        – Partition walls in corridors should reach right up to the
                                                                    structural ceiling. Structural fire protection
Most of these directives relate to the requirements for          Stairwells are areas of particular importance, since they
structural fire protection, including the rescue routes.         must usually permit safe evacuation of the building in the
The examples described in the preceding section clearly          event of a fire. Their number depends on the area, height
show, both in a positive and negative sense, how import-         and shape of the building. Several stairwells are normally
ant it is to meet these requirements.                            required.
                                                                 Stairwells must have fire-resistant walls of non-combust-
FIRE-RESISTANT MATERIALS                                         ible materials. Internal stairwells may only be reached via
To ensure the stability of a high-rise building in the event     lobbies sealed by smoke-tight self-closing and at least fire-
of a fire, the supporting structure and ceilings must be re-     retardant doors.
sistant to fire. The characteristic “fire resistant” must be     Smoke vents must be installed at the top of all stairwells;
defined in the applicable standards. However, this means         internal stairwells must be equipped with a mechanical,
that the requirements to be met by fire-resistant parts can      automatically activated ventilation system connected to an
easily differ from one country to the next, depending on         emergency power supply. If a fire breaks out, excess pres-
the standards applied. The same holds true for the inspec-       sure must be generated in the stairwells to prevent the in-
tion procedures specified for verification.                      gress of smoke.
4 Risk potential                                                                                                           Page 108

VENTILATION AND AIR-CONDITIONING SYSTEMS                 Active loss-prevention measures
Ventilation and air-conditioning systems must be installed
in such a way that fire or smoke cannot be transmitted to         STANDBY POWER SUPPLY
stairwells and other floors or fire compartments. The             Standby or emergency power supplies must be installed
cases outlined above clearly show how difficult it is to          in high-rise buildings from a specified height onwards.
meet this requirement. Stairwells, lobbies, safety locks and      These power supplies operate independently of the public
elevator lobbies must be equipped with ventilation                grid; following a power failure in the public grid, they auto-
systems which are isolated from other systems.                    matically switch on to supply electric power to all safety
As a rule, several floors are normally combined into one          equipment:
area for the ventilation and air-conditioning systems. To         – fire-detection and gas-alert systems;
prevent fire and smoke being transmitted via the ventila-         – fire pumps and their control systems;
tion ducts, fire dampers must be installed in the fresh air       – firemen’s lifts and passenger elevators;
and exhaust air ducts on each floor; these fire dampers           – ventilation systems, as well as smoke and heat vents;
must be activated automatically by smoke detectors as             – fire-resistant sealings of openings;
well as manually.                                                 – emergency lighting for rescue routes;
More stringent requirements must be imposed on the                – electroacoustic alarm systems and/or paging systems.
stairwells in taller buildings (safety stairwells). In particu-   The equipment providing the standby power supply must
lar, the safety locks outside the stairwells must be              be isolated from the general power supply and protected
equipped with mechanical ventilation systems.                     by fire-resistant materials.

SHAFTS AND ELEVATORS                                              FIRE DETECTORS
To prevent fire and smoke spreading vertically inside a           The importance of rapid and reliable detection and report-
building, the continuous installation shafts for ventilation,     ing of fires has already been highlighted in the preceding
electric power, telecommunications, sanitation and docu-          section. In larger high-rise buildings, it is therefore essen-
ment conveyors must be of the same fire-resistant design          tial to install an area-wide automatic fire-detection system
as the stairwells. Cable ducts should be sealed with fire-        which triggers a fire alert on the building’s central control
resistant elements on every floor. Openings must be               panel. This central control panel should preferably be lo-
sealed with fire-resistant doors or flaps. Automatically ac-      cated on the ground floor or in a permanently manned se-
tivated smoke and heat vents must be installed here too.          curity centre. Automatic or manual signalling of an alarm
Waste-disposal chutes must be protected in the same way.          to the local fire brigade – preferably via a direct line – de-
Elevator shafts must also be enclosed by fire-resistant           pends on the conditions prevailing on site. The security
walls; access to the elevators must be restricted to the cor-     and maintenance personnel must have clear and precise
ridors or enclosed lobbies. Elevators should be connected         rules of conduct; they must also be fully familiar with
to the standby power supply so that they can automatical-         these rules so that human error can largely be excluded.
ly be lowered to the ground floor following a power failure       Automatic fire-detection systems should be installed in ad-
or fire alarm.                                                    dition to the existing sprinkler systems, since the latter’s
Firemen’s lifts must be installed so that the firemen can         fire-detection sensors are only tripped much later – by the
arrive at the scene of a fire without delay; this is already      heat of a fire – and trigger an alarm when the sprinkler
specified by public authorities in certain standards and          nozzles open.
directives. The time lost in fighting a fire due to the ab-       The type of smoke or heat detector to be used must be
sence of such firemen’s lifts has already been shown by           determined according to suitability in each individual in-
the cases described above.                                        stance. Manual detectors – e.g. push-button fire detectors
According to the German directives governing high-rise            – must be installed in addition to automatic detectors so
construction, a firemen’s lift is required for all buildings      that fires can also be signalled by the people present.
over 30 m high. Additional firemen’s lifts may be specified       These detectors should preferably be located in a prom-
for buildings over 100 m high.                                    inent position in the corridors and rescue routes, as well
Every firemen’s lift must be located in a separate fire-          as in the lobbies to stairwells.
resistant elevator shaft. The associated equipment rooms          The installation of automatic fire or smoke detectors is
must likewise be of fire-resistant design and sealed by fire-     problematical due to the presence of ventilation and air-
resistant elements. In many cases, these lifts are addition-      conditioning systems in high-rise buildings and the asso-
ally equipped with rescue materials and radio equipment.          ciated air streams. Appropriate specialist companies are
Lobbies with fire-resistant walls and at least fire-retardant     consequently considering the use of highly sensitive
doors must be provided at the stopping points for the             smoke detectors (HSSD) and very early smoke detection
firemen’s lifts. A mechanical ventilation system must also        apparatus (VESDA). With such apparatus, detection of the
be provided. The required electrical switchgear and supply        smoke at a very early stage in the fire could be used to
lines must be physically separated from other systems             activate the fire dampers and then to switch off the air-
and lines. It is also important to ensure that the firemen’s      conditioning.
lifts are connected to the standby power supply specified
for the building or that they can be operated via perman-
ently charged batteries.

                                                                                                        70 ATRIUM IN A BANK BUILDING
4 Risk potential                                                                                                         Page 110 Fire fighting                                            to control a fire in full flame, for instance if it leaps from a
                                                                 floor with no sprinklers to one with sprinklers. Sprinkler
FIRE EXTINGUISHERS                                               systems are simply not dimensioned to cope with such
Hand-operated fire extinguishers must be installed at            developments.
clearly marked and generally accessible points in high-rise      Sprinkler systems must meet the following requirements:
buildings in order to fight incipient fires. These extinguish-   – they must rapidly control a fire in the fire compartment
ers are intended for use by the building’s residents. How-          in which it breaks out;
ever, teams should be present on every floor made up of          – they must limit the emission and spread of flames, hot
the people who work and live there; they must then be in-           fumes and smoke;
structed on what to do if a fire breaks out and also be fa-      – they must trigger an alarm in the building, preferably
miliarized with the use of these hand-operated fire extin-          also indicating to the central control panel where the
guishers.                                                           seat of the fire is located;
                                                                 – the alert must be forwarded to the fire brigade or other
FIRE-FIGHTING WATER                                                 auxiliary forces.
The cases outlined above have shown how important it is          The ability of the system to indicate to the central control
to have an effective supply of fire-fighting water when          panel where the seat of the fire is located presupposes
combatting a fire in a high-rise building. So that the fire-     that a separate sprinkler system with an alarm valve is
men can start to fight the fire as soon as they arrive on the    assigned to each floor and to each fire compartment. As
scene, wet risers must be installed in every stairwell or in     already mentioned in connection with fire-detection
their vicinity and a wall hydrant with hose line connected       systems, the installation of an automatic fire-detection
to these risers on every floor. The hoses must be suffi-         system in addition to the sprinkler system is advisable so
ciently long to direct fire-fighting water to every point on     that fires can be discovered and signalled more quickly.
that floor. An adequately dimensioned water line and ade-        Sprinkler systems must be installed in accordance with the
quate water pressure must be ensured when planning and           applicable directives or standards, the best known of
designing the building. In very high buildings, booster          which include NFPA, CEA, FOC and VdS. All the compon-
systems must be installed in the wet risers to increase the      ents used for installation must comply with the relevant
water pressure.                                                  standards.
Whether the water for fire fighting can be taken from the        The various directives and standards permit a variety of
public mains or from separate water reservoirs or tanks          solutions with regard to the water supply:
must be decided in each individual instance in accordance        – water supply from the public mains – possibly via an
with local conditions and regulations.                              intermediate tank on the ground – via booster pumps on
For greater safety, it may be useful to install not only wet        the ground to supply several groups of floors with dif-
risers, but also dry risers into which the fire brigade can         ferent pressure levels
feed water at the required pressure from the ground floor.       – intermediate tanks on various upper floors, under either
                                                                    normal pressure or excess pressure, to supply the
SPRINKLERS                                                          sprinkler groups above or below
An automatic sprinkler system is the most effective pro-         – deep tanks and pressurized tanks on the roof, as well as
tective measure for fighting and controlling a fire in a high-      intermediate tanks in the middle of the building, to sup-
rise building. Care must be taken to ensure that the com-           ply the sprinklers below with static or high pressure
plete building is protected by such sprinklers. In the cases     Tanks on upper floors can be replenished via low-capacity
outlined above, there were either no sprinklers at all or no     pumps. Depending on the type of supply selected, it may
activated sprinklers on the burning floors. In the case of       be necessary to install pressure-reducing valves on the in-
“One Meridian Plaza”, the fire was subsequently brought          dividual floors.
under control with the aid of the sprinkler system and an        For a sprinkler system to operate smoothly, it must not
additional supply of fire-fighting water.                        only be correctly installed and set, but also be regularly
Based on past experience, the installation of sprinkler          inspected and serviced by specialist personnel.
systems is in many countries prescribed by law for high-
rise buildings from a certain height onwards – as from           OTHER FIRE-FIGHTING EQUIPMENT
60 m in Germany, for example. In some cases, the statu-          Other automatic fire-fighting equipment may be appropri-
tory regulations even stipulate that sprinklers have to be       ate for certain systems in a high-rise building, such as
installed retroactively in high-rise buildings erected be-       transformers, electrical switchgear and control rooms,
fore the regulations came into force.                            computer centres and telephone switchboards. Depending
Automatic sprinkler systems throughout the building are          on the systems concerned, CO2 or – if still permitted by
important since they must fight a fire as early as possible      law – halon fire extinguishers are two possibilities worth
and must either extinguish the fire directly or keep it          mentioning here, as well as extinguishing systems based
under control until the fire brigade arrives to finish off the   on inert gases.
job. However, a sprinkler system will normally be unable
Page 111                                                                                                           4 Risk potential Organizational measures                                     ings, for example, have an immensely important effect on
                                                                    the active wind and flow conditions. The location of the
As already mentioned, emergency and alarm plans must                building – on open ground or surrounded by other high-
be drawn up in consultation with the relevant authorities           rise buildings – has a massive influence on the wind pro-
and auxiliary forces, especially the local fire brigade. So         file. The effect of wind separating off the edges of neigh-
that all fire-protection facilities are fully functional when       bouring buildings, reduced wind velocities due to obs-
required, they must be regularly inspected and serviced.            tacles at ground level and effects similar to friction or de-
The test and maintenance intervals applicable to the differ-        flection of the wind loads due to neighbouring buildings
ent facilities and systems must be scrupulously observed.           cannot be taken into account in the standard loads.
It is also important to ensure that the maintenance and             Local wind effects have repeatedly been observed in the
security personnel know what procedures to adopt in the             canyons formed by skyscrapers in large cities. One such
event of an alarm or fire, reinforced by recurrent staff fire       effect is known as the “spinning effect”, a tornado-like
and safety training at regular intervals. The catastrophic          effect near ground level which affects pedestrians. In by-
consequences due to taking the wrong action have already            gone days, the strong upwinds encountered on the Flat-
been outlined in Section 4.2.4.                                     iron Building in New York used to cause not a few ladies
                                                                    considerable problems as they strolled past. It is also Atriums                                                     known as the Marilyn Monroe effect in construction aero-
The situation described in Section 4.2.2 with regard to at-         The shape of the building is another factor influencing the
riums also poses an additional risk for people during the           wind forces actually at work. When wind meets an obs-
building’s occupancy as a hotel or department store, for            tacle, it normally generates compressive forces on the
example. Atriums in particular have a magnetic effect and           windward side of the building and suction forces on the
a concentration of visitors and customers is consequently           leeward side. In addition, air streaming around the build-
to be found in these areas.                                         ing produces suction forces on the sides parallel to the
A number of special requirements must be met in order to            wind direction. The shape of the corners and edges of the
ensure personal protection.                                         building is particularly important. Separation effects can
The required rescue routes must not be directly linked to           cause suction and compressive forces several times great-
the atrium. Instead, they must lead away from the atrium,           er than the original dynamic pressure. The magnitude of
towards the outside walls of the building. This conse-              these edge and corner forces depends primarily on the
quently means that the stairwells should be located along           geometry of the building round which the air flows. Basic-
the outside walls to keep them clear of smoke and to per-           ally, it may be said that the more sharp-edged and irregu-
mit more effective illumination in the event of a power             lar the building is, the more irregularly the wind forces
failure.                                                            will be distributed.
Flashover from one floor to the next must be prevented in           Suction forces cause major problems around the roof in
the atrium area. This can be achieved, for example, by in-          particular. If the roof structure has not been adequately an-
stalling fire-resistant glazing. The supporting elements            chored, parts of the roof may be lifted off and catapulted
must also be at least fire-retardant to prevent the top of          away unhindered. In addition to the roof, such elements as
the atrium crashing down onto the inner area.                       light-metal facades, antennas, promotional signs and
Care must also be taken to ensure that smoke is adequate-           water tanks are some of the parts most seriously threat-
ly discharged in the event of a fire. This is particularly diffi-   ened by wind on high-rise buildings. The risk of parts
cult on account of the large volume and resultant dilution          being blown away and flying around is greatest during the
and mixing of the smoke. Frequently, discharging the                construction phase. Such parts can cause considerable
smoke via a smoke and heat vent will suffice; in critical           property damage to their surroundings, and harbour
cases, however, an additional mechanical means of dis-              potential for bodily injury which cannot be neglected.
charging the smoke must also be installed.                          During the autumn gales in 1972, for example, several
                                                                    hundred glass elements worked themselves loose from
4.3 Windstorm                                                       the outer facade of the John Hancock Tower in Boston and
                                                                    crashed down onto the pavement. An area of 50,000 m2
Each of the two twin towers of New York’s World Trade               had be reglazed. Facades and roofs are also exposed to
Center, which will be discussed in more detail in the fol-          driving rain and hail. “Updraughts”, which cause the rain
lowing sections, has a base area of roughly 4,200 m2. That          to move upwards instead of down as a result of different
is roughly equal to a square base measuring 65 m 65 m.              inner and outer pressures, can cause moisture to penetrate
The towers are 417 m and 415 m high, respectively.                  inside the building. No fewer than 5,000 panes had to be
Using the highly simplified wind load permitted by Ger-             replaced for this reason on the UN Secretariat Building in
man standards, this yields a total static load of roughly           New York in 1952.
4,500 tonnes per tower from dynamic pressure and wind               A purely structural consideration of the wind will not suf-
suction.                                                            fice in the case of larger building structures. Wind is a
These values do not, however, include the conditions                phenomenon which varies strongly in strength and direc-
prevailing locally which must be taken into account when            tion and can produce dynamic effects in combination with
designing a high-rise building. The building’s surround-            vortices separating off from the buildings around which
effects from friction impact wind speed

  Wind load
  W (kN/m)
                                                     Height h (m)

                                                Horizontal load H = W x H

                                                Bending moment M = W x h2

                                        Core to stiffen
                   Wind                 the building


                                          Ground-bearing pressure
                                          from vertical load

                                          Ground-bearing pressure
                                          from wind

                                          (Ground-bearing pressure
                                          from vertical load and wind)

4 Risk potential                                                                                                       Page 114

the air flows. Particularly in the case of slim buildings cap-   The main problem for the planning engineers are not the
able of vibration, such as towers, smokestacks and sky-          horizontal loads but the much more complicated question
scrapers, this can lead to stresses which must not be            of transmitting the bending moment due to these loads. In
neglected. These vibrations are particularly critical when       the case of a uniformly applied area load, for example, the
the wind excites the building to vibrate at its resonant fre-    horizontal load acting inside the building will represent a
quency, thus producing the resonant effects already men-         linear function over the height of the building, while the
tioned in Section 3.1.3. In response to these fluctuations in    bending moment increases quadratically in proportion to
the wind, the building begins to vibrate and can continue        the building height. This means that the bending moment
to do so until the vibrations reach an amplitude threaten-       increases much more strongly than the horizontal load
ing the building with collapse.                                  with every additional metre in height. More and more so-
There are also other, less spectacular problems to be            phisticated solutions must be found for these loads to be
solved by the planners. Depending on their frequency and         controlled by the supporting structure of a skyscraper.
amplitude, vibrations will be perceived by the building’s        Supporting structures of the type developed in particular
users. These vibrations can become unpleasant or even in-        by the architects Skidmore, Owings & Merrill (SOM), such
tolerable when they reach a certain limit which, however,        as the “tube” (e.g. World Trade Center, New York), the
is normally still far away from threatening the stability of     “bundled tube” (e.g. Sears Tower, Chicago) or the “truss
the building. In the 1970s, for instance, this resulted in one   tube” (e.g. John Hancock Center, Chicago), have been pro-
of the greatest “building losses” anywhere in the world:         duced as a result of the problem that conventional sup-
due to wind vibration, almost all the tenants moved out of       porting structures are no longer in a position to transmit
a high-rise building as if in panic, resulting in a loss of      the wind loads safely (see Section
roughly US$ 75m in lost rent.                                    In the subsoil, the bending moments caused by wind must
Such dynamic effects can be counteracted by changing             be absorbed by soil pressures which can lead to consider-
the rigidity of the building or by installing active or pas-     able pressure on the leeward side of the foundations.
sive damper systems. Passive dampers include baffle              So far, we have only considered “normal windstorm
plates, for example, to reduce vortex formation. Active          loads“. If we consider, however, that many of the metro-
systems can be made up of water tanks, movable weights           politan centres with skylines dotted with skyscrapers are
or rotating unbalanced flywheels.                                located in areas exposed to severe windstorms – Hong
Shortly after completion of the John Hancock Tower in            Kong and Tokyo, for instance, are located in the track of
Boston in the early seventies, it was found that gales           typhoons and even New York can suffer a hurricane, while
caused enormous vibrations in the tip of the tower. A            Chicago is exposed to tornadoes – then it becomes clear
damping system comprising a 600-tonne counterweight              that the planning engineers must also consider this prob-
which can be moved around as required in accordance              lem. The high wind speeds associated with typhoons, hur-
with the wind direction had to be installed on the 58th          ricanes and tornadoes are not the only problem: a tor-
floor. It was discovered that the building could have top-       nado, for instance, can cause a sudden pressure drop of
pled over at any time. To everyone’s surprise, however, it       up to 10% of the atmospheric pressure within only a few
would have fallen onto its narrow side, rather like a book       seconds, with the result that the outer skin of “airtight”
falling onto its spine.                                          buildings literally bursts – and that applies particularly to
Damping systems are always based on a similar principle.         the windows.
A large mass is moved by hydraulic computer-controlled           Compared with the simplified wind load assumed in ac-
equipment or pendulum constructions in the direction op-         cordance with German standards, this would lead to an
posite to the actual direction of vibration by the building.     actual assumed wind load of around 10,000 to 13,000
The vibration energy of the wind is absorbed in this way.        tonnes for New York’s World Trade Center if we were to
The amplitudes and horizontal acceleration forces are re-        take into account all the effects mentioned in this section.
duced considerably, thus also largely eliminating the effect
of dynamic forces.                                               PRECAUTIONS DURING CONSTRUCTION
It can be extremely complicated to take wind loads into ac-      The loss potential during construction is an aspect which
count in calculations, and it is therefore almost standard       cannot be neglected.
practice today to test the response of a high-rise building      Although the stability of the building during the various
in the wind tunnel first. As already mentioned in Section        construction phases is documented by corresponding
3.1.3, even computer simulations cannot always provide a         structural analyses, such equipment items as facade
satisfactory answer to the problem. Over the years, this         elements or temporary structures are usually not taken
has given rise to a separate engineering discipline – model      into account, or only inadequately.
analysis – to solve the structural and dynamic problems of       Additional precautions must therefore be taken during the
a building on the basis of miniaturized models.                  construction work, particularly if the contractor is given
The widespread belief that it is sufficient to divide all the    sufficient advance warning of an impending windstorm.
parameters of the original by the same factor in order to        A loss of more than DM 5m was incurred during construc-
obtain an adequate model is unfortunately not correct.           tion of a 90-storey high-rise building in the Far East. Sub-
Complex mathematical problems are frequently encoun-             contractors had temporarily stored such electrical installa-
tered when drawing up models and it has taken a long             tion material as control cabinets and relays on the upper
time for model-making to become a precise science.               floors of the building shell, but delivery bottlenecks led to
Page 115                                                                                                        4 Risk potential

a delay in assembly of the facade elements on these            buildings varies. The damage depends more on the rate of
floors. A considerable proportion of the electrical material   motion and magnitude of the displacement than on the
stored on these floors was soaked by Typhoon Herb as it        acceleration. The most important and most serious effects
passed over in 1996 and consequently exposed to the risk       are outlined below, together with the possible protective
of corrosion. Since the damage was foreseeable and pre-        measures.
cautionary measures were not taken, the insurer was only
obliged to indemnify part of the loss under the policy.        SUBSOIL
                                                               Natural rock is the best subsoil from the point of view of
                                                               its earthquake properties. Sandy soils saturated with water
                                                               and artificially backfilled land are considered to be particu-
                                                               larly critical. The widely-feared liquefaction effects (plasti-
4.4 Earthquakes                                                cization of the soil) can occur if an earthquake coincides
                                                               with high groundwater levels. The building may subse-
The Richter scale is a logarithmic scale for determining the   quently remain at a slant or both the building and the sur-
energy dissipated in an earthquake. This means that an         rounding terrain may subside. The importance of the sub-
earthquake measuring 7 on the Richter scale dissipates         soil was revealed in particular by the earthquake in Mexico
32 times the energy of a size-6 quake, while one measur-       in 1985. The epicentre of the earthquake was located near
ing 8 dissipates roughly 1,000 times as much energy.           the Pacific coast, at Lázaro Cárdenas. The intensity of the
The energy dissipated by these earthquakes is expressed        earthquake decreased rapidly as the distance from the epi-
in horizontal and vertical acceleration forces acting on the   centre increased, but then rose strongly (up to 3 points on
skyscrapers. The immense forces transmitted from under-        the modified Mercalli scale) in Mexico City, some 350 km
ground must be absorbed by the supporting structures of        from the epicentre. The main reason for this increase lay
the buildings. These dynamic loads are replaced by struc-      in the fact that Mexico City is built on the soft sediment of
tural equivalent loads in horizontal and vertical direction    a dried-up lake, a subsoil that massively reinforces the
when a structural analysis of the building is performed.       effect of the incoming seismic waves through resonant
The highest acceleration forces measured to date in an         vibration.
earthquake were recorded during the Northridge earth-
quake in Los Angeles (17th January 1994) and amounted          FOUNDATIONS
to 2.3 times the acceleration due to gravity “g” (g =          Deep foundations generally display better seismic resis-
9.81 m/s2) in horizontal direction and 1.7 times the accel-    tance than shallow foundations. Floating foundations can
eration due to gravity in vertical direction. In simplified    prove advantageous on soft ground, since they may be
terms, this means that the planning engineers would add-       better able to attenuate resonance action. The risk of sub-
itionally have to apply roughly 2.3 times the dead weight      sidence is considerably greater with floating foundations
in horizontal direction and roughly 1.7 times the dead         than with deep foundations.
weight in vertical direction to the building when dimen-       “Base isolation” is an anti-seismic construction technique
sioning the supporting structure so that these earthquake      that uses the principle of attenuation to reduce vibrations.
forces can safely be absorbed. Such values are fortunately     The building is isolated from the solid subsoil by damping
exceptional. Moreover, they only act on the supporting         elements arranged on a foundation ring or foundation
structure very briefly and are subject to rapid changes        plate. Another version was employed for the Court of Ap-
of direction. The values assumed in the majority of stand-     peals in San Francisco: the building was retroactively
ards correspond to between 5% and 10% of the acceler-          more or less mounted on ball bearings which are intended
ation due to gravity. Assumed loads of up to 0.4 g are re-     to gently damp down the impact of a future earthquake.
quired in extreme cases and US standards already include       The requirements to be met by all the various anti-seismic
more recent earthquake zones in which even higher values       bearings are set out, for example, in the Uniform Building
must be assumed in certain frequency ranges. In spite of       Code (Division III, 1991).
this, however, experts still doubt the adequacy of these       When using these methods, it is important to ensure that
assumed loads under certain conditions.                        the damping system is correctly attuned to the applied
                                                               frequency spectrum and to the resonant frequency of the
HOW DO SEISMIC LOADS ACT ON A BUILDING?                        building. Resonance action can be avoided in this way.
The horizontal and vertical acceleration of the subsoil due    As in the case of wind loads, earthquakes can also give
to an earthquake causes the building to vibrate.               rise to resonant vibration. These are described in more
In simplified form, these loads can be represented by hori-    detail in Section 4.3. The resonant frequency and conse-
zontal and vertical equivalent loads acting on the mass        quently also the resonance effects can be influenced with
centre of gravity of the building. The magnitude of these      the aid of damping systems. In addition to the isolation
equivalent loads depends directly on the mass of the           systems for foundations mentioned above, vibrations can
building. This leads to the conclusion that as the height of   also be damped by using heavy moving counterweights.
the building increases, the mass centre of gravity normally    “Soft” skeleton structures have a period of fundamental
wanders upwards and the flexural effect on the building is     natural oscillations equal to roughly one-tenth of the num-
intensified by the longer lever arm.                           ber of floors in seconds. The period of a 15-storey building
The potential earthquake damage suffered by high-rise          consequently equals roughly 1.5 seconds. Higher edifices

                              HIGH-RISE BUILDING
                                                                  Static equivalent system

                                                                                       V = ay x g

                                                           H = aH x g
                                                                                       Mass centre of gravity

                                                                                                 H = horizontal equivalent load
                                                   Horizontal (aH)
                                                          +                                            which acts on the mass centre
                                                   Vertical (aV)
                                                                                                       of gravity

                                                                                                 V = vertical equivalent load
                                                                                                       which acts on the mass centre
                                                                                                       of gravity

                                                                                                 h = building’s own weight

                                                              75 50 T AND/OR 90 T HEAVY DAMPERS TO BE INSTALLED IN TWO JAPANESE HIGH-RISE BUILDINGS
                                                                                           TO REDUCE RESONANCE VIBRATIONS CAUSED BY EARTHQUAKES
4 Risk potential                                                                                                       Page 118

require a certain time before they oscillate at maximum           The system of active variable stiffness (AVS) is one such
amplitude. This excitation period lies between 20 and             system. With this system, the rigidity of the building is
30 seconds. Enduring earthquakes, such as that in Mexico          specifically varied by securing the bonds to the members
City in 1985 (around 3 minutes), consequently represent a         of the frame structure by means of a variable connection
particularly high risk. A so-called whiplash effect was ob-       which is essentially made up of hydraulic cylinders con-
served in the high-rise buildings in Mexico City, for ex-         trolled via valves. An operating power of 20 W is sufficient
ample, as the buildings abruptly moved back from their            for this purpose.
maximum deflection. Extremely high acceleration forces            The incoming seismic vibrations are detected by sensors
and consequently high horizontal forces were involved             which transmit the information to a central computer. The
here and resulted in damage to the upper floors, including        computer determines the required rigidity and opens the
such superstructures as tanks and antennas.                       valves at the individual points to increase the building’s
                                                                  flexibility in these areas. This ensures that the vibrations
HEIGHT OF THE BUILDING                                            are optimally damped and overstressing is avoided.
Tall buildings are more susceptible to damage from strong
remote earthquakes than from weak earthquakes close at            SYMMETRY
hand. They normally have a lower resonant frequency and           Symmetric layouts, rigidity and mass distribution lead
a lower attenuation than low buildings. Short-wave oscilla-       to a considerably better seismic response than asymmetric
tion components in earthquakes are rapidly damped, while          layouts, rigidity and mass distribution. This is because
the long-wave components (frequency f < 1 Hz) can still           asymmetric buildings are subjected to stronger torsion
make themselves felt at a distance of several hundred kilo-       (twisting) around the vertical axis by horizontal seismic
metres, particularly in the form of surface waves.                loads.

SUPPORTING STRUCTURE                                              SHAPE OF THE BUILDING
A distinction can generally be made between rigid and             When parts of different height are permanently connected
elastic supporting systems. Rigid systems, such as solid          to one another as, for example, is often found in high-rise
wall and ceiling elements, are difficult to deform and            buildings with atriums, then the various structures in
transmit the seismic loads through their rigidity. Due to         the building can be subjected to considerable torsional
the stiffness and lack of ductility in the supporting struc-      stresses by the seismic loads. Buildings of different
ture, however, shear cracks can develop in the building.          heights can also be subjected to a whole series of effects
The problem is that more and more energy must be ab-              in an earthquake, such as the jackscrew effect observed
sorbed through the high rigidity and that more and more           in Mexico City in 1985: higher buildings were literally
material is required for this purpose.                            jammed in between lower buildings, thus extensively
Elastic supporting structures, such as reinforced concrete        damaging the floors at the clamping point. In some cases,
or steel frames, are highly deformable and absorb the ap-         the buildings simply buckled over at the edge of the lower
plied seismic energy in this way. The nodes connecting            adjacent buildings. Resonance effects can also cause
the horizontal and vertical elements of the supporting            buildings to oscillate so strongly that they hammer against
structure are highly stressed, however, and peak loads            one another. Another effect observed in high-rise build-
occur both here and on the reinforcing elements (bonds)           ings is the soft-storey effect: due to lobbies, atriums or
which must be taken into account when producing these             glazed shopping passages, some floors – usually near the
connections. However, integrated non-supporting partition         ground floor – are distinctly “softer” than those above
walls may suffer excessive stresses and break out on ac-          them. These “soft” floors then collapse in an earthquake.
count of the major deformation of the frame structure.            A further source of loss potential relates to the standards
Skyscrapers with steel frames were hitherto considered to         applied. Many countries do not have their own earthquake
be particularly resistant to earthquakes, but the Northridge      standards and simply adopt the corresponding regulations
earthquake in January 1994 brought new insights. In an            from others, such as the Uniform Building Codes from the
unexpectedly large part of the flexurally rigid steel frame       USA. This means, however, that common local seismic ef-
structures, cracks were found in the welds in the corners of      fects are not covered. Moreover, application of the stand-
the frames. Comprehensive studies were undertaken to de-          ards is not mandatory in many countries and their super-
termine the causes and lay down rehabilitation measures.          vision not sufficiently stringent. One of the main problems
This strong earthquake also showed that steel supporting          that is repeatedly found in conjunction with earthquake
structures do not immediately come crashing down when             damage lies in the quality of the work. Poor-quality mater-
overstressed and that plastic supporting reserves are acti-       ials, poor training from the engineers to the workers, cor-
vated first. The ductility and load-bearing capacity of rein-     ruption and the pressure of time must be mentioned in
forced concrete frames, however, can be improved by in-           this context.
creasing the percentage of reinforcement. When over-              “Only fools, liars and charlatans predict earthquakes”, ac-
stressed, the concrete will usually fail at the risk of a total   cording to C. F. Richter, the man who gave his name to the
collapse.                                                         Richter scale.
A number of systems based on the principle of flexibility         New and potentially promising methods are being devel-
and energy absorption are currently being developed to            oped in the meantime, but the question remains whether
protect buildings against seismic activity.                       these methods can ever be properly applied in practice.
Page 119                                                                                                        4 Risk potential

Such predictions are naturally of subsidiary importance        and technically almost impossible on account of the high
where physical losses are concerned, such as a cata-           vertical loads to be applied.
strophic loss estimated at up to US$ 3bn in the metro-         Instead, the load-bearing capacity of the deep foundation
politan district of Tokyo. Where personal protection is con-   is determined in addition to routine investigation of the
cerned – and up to 600,000 fatalities are assumed for the      drilling explorations (assessment of the soil strata encoun-
aforementioned scenario – such precise earthquake fore-        tered). The integrity of the respective pile and diaphragm
casts would be of inestimable value.                           walls can be continuously monitored with the aid of such
                                                               special methods as ultrasound; special pipelines are inte-
                                                               grated into the foundation structures to permit a certain
                                                               degree of rework if defects arise, for instance by means of
4.5 Foundations, settlement and subsidence                     subsequent injection.
                                                               Although such complex foundation work can only be
4.5.1 Foundations                                              undertaken by highly specialized and experienced civil
Particular attention must be paid to additional foundation     engineering contractors, mishaps occur all the time. When
measures (see Section 3.2.1) when erecting a high-rise         producing the trenches for the diaphragm walls, for in-
building and above all if it is to be built on poor or dam-    stance, or when drilling holes, particularly at great depth,
aged subsoil.                                                  opened fissures or existing but undetected channels result
Foundation structures up to 100 m deep and known as            in loss of the bentonite supporting slurry, thus jeopardiz-
“barrettes”, each comprising four diaphragm wall elem-         ing the stability of the trench or hole or even causing it to
ents, were required to transmit the loads safely into nat-     collapse.
ural foundation soil under the Petronas Towers in Kuala        The long cages of reinforcing steel can become wedged
Lumpur, Malaysia, which we have already mentioned              against the wall of the deep trench or drill hole, making it
above. Load tests should really be performed on such           impossible to lower them to the required depth. It is not
foundation structures before starting the high-rise con-       uncommon for the freshly positioned reinforcing cage to
struction work, but they are economically unacceptable         be pulled upwards a short distance when the casing string

                                                                                                    77 EARTHQUAKE IN KOBE, JAPAN
Page 121                                                                                                         4 Risk potential

is raised after completing the pile. This can impair the in-     other structural measures, such as the use of hydraulic
tended load-bearing capacity or even make it necessary to        jacks.
abandon the pile in question.                                    Problems only arise, however, if defective work, undetect-
The required load-bearing capacity may likewise not be           ed disturbances, subsequent changes in the subsoil or an
achieved if deviations from the vertical axis exceeding the      incorrect appraisal of the load-bearing capacity lead to
theoretically permissible limit occur as a result of encoun-     abrupt and extensive subsidence which may threaten the
tering obstacles or due to carelessness while drilling           stability of the entire building.
(sinking). This is not uncommon, particularly in the case        Such subsidence can occur during the construction phase,
of long piles.                                                   when the building has already reached a certain height
Simple repairs or reworking are rarely possible in such          and consequently also a certain weight. It may also occur
cases. Extensive supplementary measures, such as re-             after several years and may not only cause the building to
placement piles, pile bents or injections, will usually be       collapse, thus resulting in a total loss, but can also result
required on account of the simultaneous disturbance pro-         in devastating casualties.
duced in the subsoil. These supplementary measures may           The spectacular collapse of a high-rise building will in
prove considerably more expensive than the original foun-        many cases be due to a combination of causes, such as a
dation.                                                          combination of design errors, inadequate workmanship
In many cases, this will also give rise to the question          and problematical soil conditions.
whether a mere defect is involved or whether it is a phys-       Attention must be devoted to the horizontal forces in par-
ical loss with corresponding consequences for indemnifica-       ticular when designing the foundations for high-rise build-
tion under the policy. In the latter case, the indemnification   ings on sloping ground.
for such supplementary costs should be suitably limited          In one case, reject railway tracks were used as the founda-
by correspondingly worded clauses, limits or other restric-      tion element for a high-rise building instead of the usual
tions when concluding the policy before construction             steel or reinforced concrete piles. Although the tracks
starts.                                                          were welded together to give them the requisite load-
                                                                 bearing capacity, they still did not conform to the ap-
4.5.2 Settlement and subsidence                                  plicable regulations. When heavy rainfall subsequently
                                                                 caused a landslide on a nearby slope, these piles were
Settlement and subsidence are another risk. It must be           neither structurally nor theoretically in a position to ab-
pointed out, however, that a certain degree of settlement        sorb the additional active horizontal earth pressure. The
will be unavoidable in all these projects. The equilibrium       piles buckled and some sheared off, with the result that
of forces originally present in the ground is disturbed by       the high-rise apartment block literally tipped over and
excavation of the soil for the underground floors and by         then collapsed.
application of the structural loads. Depending on the type       It is very difficult to repair a high-rise building when its
of building, the soil conditions and the foundation select-      stability has been jeopardized by such severe subsidence.
ed, settlement will occur immediately or at a later date.        The defective foundations can be reinforced with the aid
Depending on the method selected (diaphragm wall, bore           of injections, supplementary piles or root piles if neces-
diaphragms), the retaining wall can also cause the ground        sary on account of the limited height available on the
to settle and result in damage to third-party property. For      underground floors. However, such measures are almost
this reason, it is advisable to record prior damage on           impossible in a completed high-rise building, due to its
neighbouring buildings as evidence before starting the           immense overall weight, and the only alternative is usual-
work.                                                            ly to demolish the building.
The planning engineer is responsible for ensuring that           Even when high-rise buildings are still under construction,
such settlement is determined correctly and for ordering         i.e. in a phase where repairs would still be possible on
appropriate structural precautions so that the settlement        account of the lower dead weight, demolition of the shell
remains within tolerable limits. This can be achieved by a       will usually prove to be the more economical, time-saving
corresponding arrangement of joints in the building and          and generally better alternative for the principal.
4 Risk potential                                                                                                         Page 122

4.6 Water                                                        building is restored to the condition of a shell and then
                                                                 refinished with corresponding installations and interior
GENERAL                                                          finishing in line with its new use.
Like other buildings, high-rise buildings can also suffer        However, if these conversions result in considerably
damage due to water. As a rule, this damage will be due          higher loads for the building, these loads will have to be
to soaking, soiling, discoloration, corrosion, shrinkage or      discharged via extended foundations in extreme cases.
expansion and mould.                                             Particular attention will have to be paid to settlement in
                                                                 this context. The problem can be minimized by providing
DEVELOPMENT OF LOSSES                                            additional piles, for example. From a technical point of
The damage is due to the interplay between the nature of         view, however, this will prove fairly difficult as the working
the media concerned (e.g. drinking water, heating water,         height of the drills is usually limited by the height of the
effluent), the quality of the installation materials, design     various levels in the underground car parking.
and execution of the plants and the prevailing operating         The fact that conversions are often undertaken while oper-
conditions.                                                      ation continues without interruption in those parts of the
In the case of high-rise buildings, the risk is further aggra-   building and on those floors not affected by the work not
vated by the fact that leaking water rapidly finds its way to    only makes the work more difficult, but also increases the
floors below the actual leakage point, with the result that      risk for the insurer. The nuisance due to noise and un-
several floors may be affected, depending on the duration        pleasant odours or temporary failure of the sanitary instal-
of the leak and the amount of water involved.                    lations, heating or ventilation are relatively harmless phe-
The considerably larger size of the installations in compari-    nomena. The dust inevitably generated by such conver-
son to “normal” buildings is another risk factor: booster        sions, on the other hand, can have serious consequences
systems and pumps, pressure reducers, etc., are all need-        if high standards of purity and hygiene must be met by
ed in order to distribute or discharge the drinking water,       those areas still in operation, such as computer systems or
heating water and effluent horizontally and vertically, thus     doctors’ offices.
increasing the number of possible leaks.                         As in the case of “normal” building work, the use of such
                                                                 flammable substances as adhesive and bituminous mater-
                                                                 ials or naked lights, for instance for soldering and welding,
                                                                 will be unavoidable when carrying out conversions. Ex-
4.7 Special structural measures                                  tremely stringent requirements must therefore be imposed
                                                                 on the fire-protection measures due to the incomparably
Considerations on the conversion, rehabilitation and final-      greater risk potential. In particular cases, the fire brigade
ly demolition of high-rise buildings have been subsumed          will have to be ready on site to take immediate action if an
under this heading.                                              emergency arises.
                                                                 Another problem associated with conversions is that the
4.7.1 Conversions                                                normally strict controls with regard to access and author-
                                                                 ization are often suspended for the conversions: workers,
Conversions are constantly being made to any high-rise           suppliers and the vehicles transporting materials and
building with thousands of square metres of useful floor         equipment need “open doors”. This naturally also in-
space. Redecoration and modernization are the common-            creases the risk of unauthorized persons exploiting the
est conversions, in addition to those necessitated by            situation and simply marching into the building.
changes in operational procedures and use of the build-          Conclusion: all conversions, no matter how slight, must be
ing.                                                             thoroughly planned in advance and organized in detail
More stringent or additional requirements in respect of          with due consideration given to all eventualities.
fire protection, installations or computer systems can also
make conversions necessary.                                      4.7.2 Rehabilitation
On the one hand, conversions and changes of use are fa-
cilitated by the separation of shell (= supporting structure),   Rehabilitation is an extreme form of conversion. The two
installations and interior finishing commonly applied in         commonest reasons making rehabilitation measures ne-
the construction of modern high-rise buildings; at the           cessary are
same time, however, it is precisely this separation that im-     – physiologically harmful materials, such as materials
poses limits on what is economically acceptable. Even if           containing asbestos or materials with excessive formal-
technically feasible, conversions involving changes to the         dehyde concentrations, or
existing structural system, i.e. to the supporting structures,   – potentially dangerous structures.
will usually be rendered impossible on account of the
costs involved. For this reason, conversions will almost al-     All the aspects already mentioned in the previous section
ways only affect the interior finishing and the installations.   also apply here in particular. In addition, there is the prob-
The range of possible conversions extends from simply            lem of disposing of the physiologically harmful materials.
relocating interior wall elements or fitting complete new        Correct disposal of contaminated materials and sub-
false ceilings or laying new floor coverings to “gutting”        stances not only poses a technical challenge, but is also
the building completely. In such a case, all or part of the      one of the most difficult jobs for third-party liability insur-
Page 123                                                        4 Risk potential

ers on account of the possible environmental impact and
health hazard.
In the majority of cases, it will be impossible to continue
normal operation of the building while the rehabilitation
work is in progress. For this reason, such rehabilitation
will usually also be associated with conversion and a
completely new interior finish.
An alternative method was employed when Winterton
House in London was rehabilitated in the 1960s. All false
ceilings and facade linings were removed first. The new
brick facade was then built up on its own foundations
around the steel supporting structure. The facade was
secured to the supporting structure by means of steel
brackets for reinforcement. An active construction was
required to compensate the differences in thermal expan-
sion of the facade and supporting structure. In this case,
the roof structure links the inner skeleton with the outer
wall via hydraulic presses. These presses are in continu-
ous duty and maintain a constant compressive strain on
the upper edge of the masonry. The building’s outer and
inner columns were reanchored in the roof structure, thus
reducing the load in the columns. Ceilings in line with
today’s state of the art were then installed.

4.7.3 Demolition

Demolition remains the method of last resort when even
changes in use, conversion and rehabilitation can no long-
er meet the more stringent requirements imposed on a
It is no longer standard practice today and in many coun-
tries even illegal simply to demolish a building – often
with the help of unskilled labourers. Experienced special-
ists are needed not only in order to meet environmental
regulations requiring that all materials and parts accumu-
lated in the course of the demolition work be carefully
sorted, but also to judge how the complex supporting
structures will react during the demolition. Within only a
few years, the demolition of a building has ceased to be
a low-tech job and become a highly specialized technical
Specialists often take over when the building has finally
been gutted, i.e. when all interior finishings and installa-
tions have been removed and duly disposed of (recycling)
and when there are no further physiologically harmful
materials in the remaining supporting structure. Either the
building is then dismantled carefully and with as little
noise and dust as possible, the reinforced concrete literally
being “nibbled away” by special machines, or – if the cir-
cumstances permit – explosives experts apply their pre-
cisely primed charges to the predetermined points after
analysing the drawings and inspecting the remaining
building. As spectacular explosions of high-rise buildings
have proved, experienced experts can make a building
collapse in such a way that the surrounding structures
remain undamaged. Less carefully planned explosions,
on the other hand, have caused serious damage to the
surrounding areas.
4 Risk potential                                                                                                        Page 126

In addition to taking into account the existing supporting       4.8 Other risks
structure, it is also important to investigate the effect of
conversions, rehabilitation and demolition work on the ex-       For the sake of completeness, mention must also be made
isting supporting structure, neighbouring buildings and          of a few other risks which, although closely associated
the site environment.                                            with high-rise buildings, either occur very rarely, such as
The most appropriate methods are then selected on the            terrorism, are unavoidable, such as wear, or are often un-
basis of such influencing factors as                             derestimated, such as the consequential costs due to phys-
– vibrations,                                                    ical damage.
– noise,
– dust,                                                          4.8.1 Terrorism
– site traffic,
– contamination.                                                 High-rise buildings with their characteristic silhouette in a
The work is preceded by detailed analyses of the existing        city’s skyline not only represent a magnet for tenants,
structures.                                                      customers and guests, but unfortunately also become a
                                                                 popular, sometimes inadvertent, target for terrorist attacks,
4.7.4 Disposal                                                   as the 1998 bombing attacks in Nairobi and Dar es Salaam
As already mentioned in the preceding section, particular        A skyscraper’s famous name is enough to assure the ter-
attention must be paid to disposal of the materials accu-        rorists of the desired media attention following an attack.
mulated in conjunction with conversions, rehabilitation          In many cases, however, the dominant presence of a high-
measures and demolition jobs. Specific reuse of the ma-          rise building will suffice to obstruct the devastating shock
terials will be unavoidable as contaminated materials must       waves of an explosion somewhere else.
be dumped on special landfills in some regions and land-
fill space for construction rubble becomes scarcer and in-       OFFICE TOWER OF COMMERCIAL UNION INSURANCE IN
creasingly more expensive.                                       LONDON
The materials must be analysed before starting the work          Precisely that was the fate of the office tower of Commer-
and classified according to their contamination, suitability     cial Union in London when a bomb exploded on the even-
for disposal and reusability.                                    ing of Friday, 10th April 1992, in the immediate vicinity of
The primary objective is to reduce the volume of contam-         this newly renovated tower with its completely new facade.
inated rubble so that it can be decontaminated (if possible),    The physical damage sustained by the building amounted
for instance by washing the soil. If this is not possible, the   to more than £40m, plus the loss of rental income during
material must be dumped on special landfills.                    the tower’s restoration. Although there is no effective pro-
The degree to which the materials can ultimately be sorted       tection against such indirect effects of terrorist attacks, the
depends on the local regulations and on the landfill capa-       crisis management set up by CU for such events passed
bilities and costs. Separating and sorting the contaminated      its first test with flying colours and saved the company
materials often entails a great deal of work.                    from potentially ruinous loss of business.
Such reusable materials as concrete, steel and PVC are           After corresponding reports in the national press and
sorted, delivered to recycling plants and reprocessed. In        thanks to availability of the complete data in Croydon, the
the case of concrete or masonry, this can also be done on        company was able to resume its business at 9 a.m. on the
site using mobile plants. The resultant materials (crushed       following Monday. The problem of such business inter-
stone, etc.) can then be used in the construction of a new       ruptions will be discussed in the next section.
high-rise building, thus also reducing the volume of traffic
on site.                                                         WORLD TRADE CENTER IN NEW YORK
                                                                 The consequences of a car-bomb explosion in the under-
                                                                 ground car park of New York’s famous World Trade Center
                                                                 on 26th February 1993 were even more devastating.
                                                                 Six people were killed in the explosion and more than
                                                                 1,000 were injured; the explosion caused immense physi-
                                                                 cal damage estimated at around US$ 500m. The bomb
                                                                 fortunately exploded around lunchtime when many of the
                                                                 offices were empty. Around 50,000 people normally work
                                                                 in the skyscraper and over 80,000 visitors are additionally
                                                                 recorded every day.
                                                                 Contrary to the recommendations of experts, there were
                                                                 no special precautions against such terrorist attacks on the
                                                                 World Trade Center with its 417-m and 415-m-tall twin
                                                                 towers and the 22-storey Vista Hotel between them. The
                                                                 emergency power generators and central water supply
                                                                 were located on the uppermost of the six underground
                                                                 floors immediately above the parking decks and therefore
Page 127                                                                                                        4 Risk potential

highly vulnerable, as this underground car park was open        most always a genuine catastrophe, possibly with numer-
to all users. Three underground railway lines also have         ous fatalities and enormous losses.
their own stations on two of these parking decks.               Two of the most spectacular cases in which an aircraft col-
When the bomb concealed in a delivery van detonated, it         lided with a high-rise building occurred in New York and
blasted a hole in the concrete floors of the decks above        near Amsterdam.
and below and left a crater roughly 30 m deep. Numerous
fires broke out on the three levels affected. Caustic smoke     EMPIRE STATE BUILDING, NEW YORK CITY
rapidly spread through service and elevator shafts in the       A light fog lay over the city on the morning of Saturday,
two towers and in the hotel.                                    28th July 1945. Visibility was no more than 2 miles,
                                                                the cloud ceiling had dropped to roughly 500 m. Shortly
FEDERAL BUILDING IN OKLAHOMA                                    before 10 a.m. a B25 bomber of the US Air Force with a
The world was even more deeply shocked by the explosi-          crew of three approached Newark airport, New Jersey, just
on of a car bomb outside the Alfred P. Murrah Federal           a few miles from the centre of Manhattan. The 12-ton
Building in Oklahoma City, USA, on the morning of               aircraft was scheduled to land at Newark a few minutes
19th April 1995.                                                later. At a cruising speed of roughly 320 km/h, the bomber
The nine-storey office building accommodated not only           crossed the East River and Manhattan above 42nd Street.
several federal authorities, but also a daycare centre for      Witnesses saw the aircraft heading directly towards a
young children. The blast killed 168 people and injured         high-rise building on Park Avenue at a height of roughly
475. The bomb with almost two tonnes of explosive had           2,000 ft. Pedestrians and shoppers saw how the aircraft
been concealed in a small closed pick-up truck parked near      just managed to evade this building at roughly the level of
the main entrance to the building. The building was posi-       the 22nd floor and then avoided colliding with another
tively “lifted” by the shock wave from the detonation and       skyscraper on Fifth Avenue. Most of the witnesses
the supporting structure so severely damaged that almost        subsequently said that it seemed as if the pilot was
one-half of every floor collapsed and the glass facade was      having technical problems. Whether that was indeed the
sheared off. The people inside the building were buried         case is still unknown today.
under the rubble. Several nearby buildings also suffered        What is known is that, for whatever reason, the aircraft
considerable damage and numerous cars caught fire. Win-         could not be pulled up in good time and drilled its way
dows shattered even at a distance of several kilometres.        into the 78th and 79th floors of the Empire State Building
Altogether 43 fire brigades and auxiliary organizations,        at precisely 9.52 a.m. Fire broke out immediately in the
many of them from other federal states, took part in the        building. The bomber’s wings broke off first. The fuselage
rescue operation which commenced immediately. Many              ripped a 6-m hole into the facade and penetrated more
people were recovered alive from the rubble. The complete       than 25 m into the building. One engine continued right
loss was estimated at more than US$ 300m, but the dam-          through the 79th floor and emerged through the outer
aged building itself was not insured. It had to be complete-    wall on the southern side of the building, from where it
ly demolished on account of the major damage suffered.          dropped onto the roof of a 12-storey building which also
What insights and conclusions can be drawn from these           caught fire. The 800 gallons of kerosene in the tanks ex-
occurrences? There is naturally no such thing as complete       ploded and totally destroyed the western half of the two
protection against the inventiveness and fanatical destruc-     floors concerned.
tive urge of terrorist attackers. Nevertheless, appropriate     The other engine made its way through an elevator shaft
security and fire-protection measures should make it more       and ultimately came to rest in a stairwell, blocking this
difficult for them to achieve their objectives.                 escape route. The suspensions on several elevators were
One such measure would be total control of all incoming         destroyed and two cabins crashed 300 m to the bottom
and outgoing people and vehicles. Thanks to the attentive-      basement floor. By a miracle, two people in the lifts
ness of the security personnel, for example, it was pos-        survived the crash with serious injuries, while 14 people
sible to defuse the bomb placed by a terrorist organization     were killed in the offices directly affected by the explosion
in a delivery van outside the new office tower on London’s      on the 79th floor. The 78th floor was fortunately only used
Canary Wharf. If such an attack cannot be prevented, how-       as a store and there were no further fatalities there.
ever, it is extremely important that the emergency plans        All in all, the catastrophe could have been even worse.
and fire-fighting measures already discussed in the pre-        Hundreds of people would probably have been killed in
ceding sections be applied and function smoothly.               the offices and on the surrounding streets on a normal
                                                                working day. The physical loss totalled around US$ 1m –
4.8.2 Impact                                                    an immense sum in those days and the equivalent of 4%
                                                                of the contract price – and it took over a year to repair the
The risk of an “impact or crash of a manned flying object       building.
or parts thereof or its cargo” which is normally included in
the insurance cover for buildings, is considered a neces-
sary but rarely claimed insurance element. The number of
losses of this type reported to date is admittedly small, al-
though the media frequently feature such “near misses”.
When an accident of this type does occur, however, it is al-
Page 131                                                                  4 Risk potential

4 Risk potential                                                                                                       Page 132

BIJLMERMEER NEAR AMSTERDAM                                        The leaning tower of Pisa, on the other hand, shows just
A Boeing 747-200 F operated by the Israeli airline El Al          how long it can take for an impending collapse actually to
with a crew of four and 320 tonnes of freight on board            take place. Due to poor soil conditions, the tower has
was on its way from New York to Tel Aviv via Amsterdam            leaned over further and further over the centuries, but it
on 4th October 1992. Ten minutes after taking off from            has still not collapsed.
Schipol Airport, the fully laden aircraft had evidently not
gained sufficient height and crashed into the two high-rise       4.8.4 Wear
buildings “Groenevenen” and “Kruitberg” in a modern
satellite town near Amsterdam. Both buildings caught fire         A high-rise building is exposed to time-dependent influ-
within seconds of the crash as a result of the full tanks.        ences during its occupancy period. Ageing processes on
According to official figures, 43 people were killed in add-      such building parts as windows, joints and seals are influ-
ition to the crew; 233 flats were destroyed. Insiders as-         enced in particular by temperature, wind, UV radiation,
sume, however, that many more people were actually                moisture, dust and gaseous emissions. They play an im-
killed, since these flats were inhabited by numerous immi-        portant part in conjunction with plastics and rubber ma-
grants and asylum seekers, and not all residents may have         terials and differ from the corrosion processes primarily
been officially registered.                                       affecting metallic materials. In the majority of cases, cor-
Not long before the accident, experts at Schipol airport          rosion of metallic materials on facades and roofs does
had considered the risk of an aircraft crashing into this         not constitute any form of wear – assuming that mistakes
residential area to be “negligible” – a disastrously false        have not been made in the planning, execution and choice
assessment, as it turned out.                                     of materials – but is instead a desired process covering the
Despite adequate lighting, inclusion in flight maps and           metals with a protective layer.
designation of air corridors with sufficient distance, high-      Inside the building itself there are numerous installations,
rise buildings will always constitute a certain impact risk if    machines and units, such as pumps, fans, compressors,
only on account of their height.                                  elevators and garage doors, the moving parts of which are
                                                                  subject to wear in accordance with their operating condi-
4.8.3 Collapse                                                    tions.
                                                                  Maintenance schedules (for maintenance, inspection and
The collapse of a building could be considered the “worst         repair) must be drawn up and observed in order to minim-
case” for everyone involved in its planning and realization.      ize the probability of losses occurring due to component
The financial consequences for its owner and the expos-           wear. Unfortunately, such intentions do not always func-
ure risk for the people inside the building and in its vicinity   tion as smoothly as with motor vehicles.
when it collapses are devastating.
The possible causes are often complex and difficult to as-        4.9 Loss of profit
certain retrospectively, but risk potential can be identified
and corresponding precautions taken.                              The risk potential and examples of losses discussed in the
The following risks are a potential source of errors during       preceding sections have focused above all on the physical
the planning and construction phases:                             damage to the building as such, while the considerable
– Flawed analysis of the subsoil                                  consequential losses following such an occurrence have
– Flawed structural analyses                                      only been mentioned in passing. This problem will now be
– Lack of coordination between the parties involved in the        discussed in more detail here.
   planning and realization (changes which are not taken
   into account, etc.)                                            CONSTRUCTION PHASE
– Defective work (stripping times, wrong quality of mater-        As already mentioned, the realization of high-rise con-
   ials, etc.)                                                    struction projects requires considerable financial resources
– Incorrect use of the building during the construction           and investments, for which interest and repayment instal-
   phase (e.g. concentrated storage of materials on floors        ments are often already due during the planning phase or
   not structurally dimensioned for this purpose)                 at the latest when the land is purchased. The owner’s pri-
During the occupancy phase, a building may collapse for           mary aim will be to ensure that the high-rise building is
the following reasons:                                            completed as quickly as possible, not only on account of
– Structural changes which have not been taken into ac-           the considerable borrowed capital and higher resultant
   count in the structural analysis of the building (e.g. by      interest burden, but also in order to make a profit. Every
   adding floors or removing supporting structures)               major loss during the construction phase will consequent-
– Poor maintenance                                                ly thwart his efforts to achieve this aim and can even
Evacuation of the people in the building depends very             jeopardize his financial survival.
strongly on the manner in which it collapses. No precau-          Particularly in the case of high-rise buildings, the investor
tions can be taken against a sudden failure of the support-       will also seek to conclude a large number of contracts with
ing structure. Cracks in the tension zone of the concrete or      future tenants or lessees during the construction phase.
plastic deformation of the steel structure could be detect-       Such contracts usually not only govern the tenancy as
ed if the building is properly serviced. It would then have       such, but also the approval for often expensive interior fin-
to be closed due to the risk of collapsing.                       ishings tailored specifically to the tenant’s requirements.
4 Risk potential                                                                                                      Page 136

Delayed completion of the building can therefore also           Investors and owners are not the only people, however,
have negative effects on the contracts already concluded,       whose fate largely depends on the profitability of a high-
as well as on the dates agreed between the tenant on the        rise building and who must precisely identify, appraise
one hand and tradesmen, suppliers or service-providers          and control their associated risks before considering a
on the other. Innumerable other consequential costs are         well-conceived insurance.
also possible, the least of which will be media advertise-      The following risk potential and other aspects must also
ments publicizing the forthcoming opening of new prem-          be weighed up by the tenants renting offices and business
ises.                                                           space in what is no doubt an attractively located high-rise
Since these are consequential losses, the best precaution       building from a strategic business point of view:
is to avoid the physical losses leading to such delays in       – If the tenants have obtained very favourable long-term
completion of the construction work. These statements              leases in the past which, however, can be terminated
thus merely serve to underline the measures already out-           prematurely on account of material physical damage to
lined in the preceding sections with regard to loss preven-        the building or to the rented furnishings, these tenants
tion.                                                              must expect to pay considerably more when renting
The possibility of covering some of these consequential            comparable business premises if rents have risen sub-
losses through corresponding insurance products will be            stantially in the meantime.
discussed later.                                                – Quite apart from the additional rent to be paid for tem-
                                                                   porary or definitive removal to alternative premises, the
OPERATING PHASE                                                    tenants concerned will possibly also have to reckon with
The main financing aspects concerning the construction             considerable additional costs for all the special meas-
phase also apply equally to the operating phase. Regard-           ures required in order (preferably within the scope of
less of whether own or borrowed capital has been invest-           contingency plans) to avoid or at least minimize any
ed, the investor will expect a guaranteed return on his            negative effects on the company’s operating and earn-
investment. Even as the property is being let, the owner           ings situation. In spite of this, however, it will probably
will therefore seek to attract solvent tenants guaranteeing        be impossible to prevent all loss of gross profit between
a profit in line with his cost calculations within the frame-      occurrence of the physical loss and restoration of normal
work of a long-term lease. This is particularly true if the        operating conditions.
owner has during the construction phase already provided        The economic environment of the high-rise construction
advance financing for complex interior finishing meeting        project must also be taken into account – depending on
the tenant’s wishes.                                            the order of magnitude in each instance. It was mentioned
The owner of a high-rise building will therefore wish to        in Section that high-rise buildings could be com-
know what impact a maximum foreseeable physical loss            pared to a “town under one roof”. The World Trade Center
due to the aforementioned risk potential could have on his      (WTC) in New York (see Section 4.8.1) is an example of
calculated revenues and expenditures:                           this economic aspect underlining the loss-of-profit risk.
– How long will it take for the property (offices and busi-     The WTC is made up of seven buildings accommodating
  ness premises) to be restored and when can they be            some 1,200 businesses on an area of 7 hectares. The two
  relet?                                                        office towers are 415 and 417 m high, respectively, and are
– Can the property be relet immediately and generate the        linked by a 22-storey hotel complex. With 110 floors, they
  calculated revenues or must rents be expected to de-          provide roughly one million m2 of useful floor space for
  cline due to the growing supply in the neighbourhood          various offices, such as investment companies, brokers,
  of the property?                                              raw commodity markets, customs authorities and televi-
– What is the term of the individually concluded leases?        sion companies. A 100-m television mast with various
– What revenues are guaranteed by these leases over             antennas is mounted atop one of the towers. The second
  their entire term? Under what conditions could a tenant       tower additionally accommodates a switchboard for New
  rescind the contract completely or insist on a pro rata       York’s telephone system with, among other things, the
  reduction in rent due, for example, to a physical loss of     telecommunications for air traffic control at New York’s
  the aforementioned type?                                      three largest airports. Underneath the extensive open-air
– What is the maximum term to be foreseen by the owner          plaza are the largest covered shopping promenade in
  of a high-rise building, i.e. from occurrence of the phys-    Manhattan, six department stores and shops, 2,000 park-
  ical loss until the calculated rent revenues are obtained     ing spaces, two vehicle tunnels and the stations for three
  again; and what losses will he in all probability have to     underground railway lines carrying the roughly 50,000
  include in his calculations during this period?               people working in the two towers and the roughly 80,000
                                                                visitors recorded every day. Numerous businesses, organ-
                                                                izations and a complex infrastructure are consequently
                                                                dependent on the smooth functioning of the two towers.
Page 137                                                         4 Risk potential

The magnitude of the direct losses caused by the car
bomb on 23rd February 1993 has already been described
in detail. Both office towers were closed by official order
until further notice.
Due to the surplus of offices available in New York City in
1993, the towers’ owner – the Port Authority Risk Manage-
ment – was naturally anxious to do everything possible as
quickly as possible in order not to lose tenants. Perfect
contingency plans meant that 220 floors were cleaned up
within only 21 days and the towers reopened for use as
offices on 19th and 26th March, respectively.
During this one-month break, the tenants in the towers
had to find alternative premises at considerable expense
and had to finance the temporary furnishings. This was
not always an easy matter in view of the special technical
equipment required in various cases. One Japanese insti-
tute quoted lost revenues in the order of US$ 12m per day,
while another cited a figure of US$ 20m daily.
The absence of the people working in the office towers in-
evitably also led to loss of profit for the other businesses
and organizations in the area and surrounding districts,
particularly the transport corporations and the toll bridges
and tunnels over and under the Hudson River, which sep-
arates New York from New Jersey. In this way, an eco-
nomic loss of roughly US$ 1bn was incurred in a one-
month period.
Particularly when assessing the loss of profit risk, it is im-
portant always to remember that “if anything can go
wrong, it will – at the worst conceivable moment – and
everything always takes longer than expected“.
5 Insurance

5.1 Property insurance
5.2 Third-party liability insurance
                                      5.3 Problem of maximum loss
                                      5.4 Underwriting considerations
                                                                        5.5 Reinsurance
Page 139                                                                                                            5 Insurance

Compared with normal building construction, there
are a number of additional risks associated with
the construction and subsequent occupancy of high-
rise buildings which can only be appraised by an
experienced insurer. The project documents provide
an initial overview of these risks.

5 Insurance

GENERAL                                                         by contractors’ all risks insurance, possibly including cover
The project documents usually only provide information          for construction and erection equipment. The second
on the finished building and how it is integrated into the      phase, however, requires a series of policies covering such
townscape. Since different methods are often employed           risks as fire, complete or partial collapse (decennial liabil-
for the construction work, the respective risk potential dur-   ity) and various additional perils (natural hazards, water
ing the construction phase must also be weighed up and          damage, glass breakage, etc.).
valued by the insurer.
Almost every blueprint of a high-rise building also in-         5.1.1 Contractors’ and erection all risks insurance
cludes a series of tailor-made elements, such as facades
or special foundations, with divergent risks which              Construction work on a high-rise building is normally
consequently can be considered a kind of prototype,             covered by contractors’ all risks (CAR) insurance. If cover-
at least in part. The effects of such semi-prototypes for       age in accordance with an erection all risks (EAR) policy
contractors’ all risks insurance must be investigated           is required in certain cases for the interior finishing, in-
separately.                                                     cluding installations for air-conditioning, electric and
At the end of the planning phase, if not before, the princi-    telecommunications systems, this can be included
pal must decide how the risks during the construction           in the CAR policy through corresponding extensions of
work are to be spread between himself and the contract-         cover without making it necessary to issue two separate
ors. This must already be specified in the tenders. Such        policies.
early and precise demarcation of risk between the princi-       A separate EAR policy is only meaningful if a strict distinc-
pal and the contractors is of great importance, not only for    tion is to be made between the structural works and the
determination of the premium, but also for subsequent           interior finishing on account of different insurance inter-
loss events.                                                    ests (principal/tenant). Since, however, it is impossible
                                                                both physically and chronologically to separate the struc-
                                                                tural works from the interior finishing, care must be taken
                                                                in this specific case to ensure that the scope of cover is
5.1 Property insurance                                          precisely defined in relation to the concurrent CAR policy.

A distinction must first be made between construction of a      GENERAL
high-rise building (construction or erection) and the sub-      Unless explicitly stated otherwise, the following com-
sequent occupancy phase. The first phase will be covered        ments apply equally to the cover granted under a CAR and
5 Insurance                                                                                                              Page 140

an EAR policy. Both policies cover the construction or             exact documentation of the final sum insured declines
erection work specified in the Schedule against unfore-            after conclusion of the construction work.
seen and sudden physical losses of every kind.
                                                                   PERIOD OF COVER
POLICYHOLDER                                                       Insurance cover is provided until the policy expires or until
The interests of all parties involved in the construction          the construction work is finally accepted by the principal
work are normally insured by the principal. The group of           or until the building is taken into service or used, if this
insured persons or companies is therefore very large; both         occurs before expiry of the policy. However, there are ex-
the principal and the general contractor are policyholders         ceptions, particularly in this context and especially if com-
in a CAR/EAR policy, although all subcontractors are also          pleted floors are let earlier in order to earn income from
covered. These are often specialists, particularly in high-        rentals or sales proceeds as soon as possible. In such
rise construction. This explains why the general contractor        cases, a clear distinction must be made between the cover
is not the only party of interest to the insurer, for the spe-     defined for the CAR policy and that of the subsequent
cial jobs undertaken by subcontractors can frequently rep-         insurance for the building. In spite of all efforts to boost
resent a greater risk. Here, too, the general contractor is        efficiency, construction work usually continues over sev-
liable as contractor to the principal. It is therefore essential   eral years, with the result that during risk assessment the
to obtain full information on the work of these specialized        construction schedule should be consulted in order to in-
companies as well, in order to appraise the physical and           clude seasonal hazards, such as monsoon rains or autumn
moral hazard.                                                      gales.
If – in deviation of the norm – only the contractor takes          Extensive preparatory work (routing of supply lines, erec-
out CAR/EAR insurance to safeguard his own interests,              tion of the retaining walls, excavation and water manage-
then the contractual agreements reached between                    ment) is necessary before work on the high-rise building
principal and contractor must be reviewed in order to as-          actually starts. Insurance cover is also required for this
sess the risk to be borne by the insurer. The risk for losses      preparatory work, since losses can arise even in this phase
due to force majeure will normally pass partly or entirely         of construction.
to the principal. This reduces the risk to the contractor’s        A so-called maintenance agreement is often concluded
insurer.                                                           between the principal and the contractor for the period
                                                                   after completion of the construction work. Under these
FORM OF COVER                                                      agreements, the contractor is obliged to remedy any
It concerns all-risks coverage, i.e. every cause of loss is        defects occurring in the building during the term of the
covered unless explicitly excluded. This naturally means           maintenance agreement (usually 12 months). Two types of
that the insurer must take account, in particular, of the          insurance cover can be granted for property losses in this
risks from ground and soil and the exposure due to nat-            period:
ural hazards, especially windstorm and flooding. The terms         – Insurance of physical losses following maintenance
of insurance must be clear. In very rare cases, it may be             work (Clause 003: Maintenance visits), or
necessary to introduce a limit of indemnity for losses due         – In addition to the aforementioned cover, insurance of
to natural hazards, such as earthquakes. This may be ne-              physical losses occurring during the maintenance period
cessitated by inadequate capacities or uncertainties when             but caused by an event originating in the construction
estimating the possible maximum loss.                                 phase (Clause 004: Extended maintenance).

SUM INSURED                                                        LOSS ADJUSTMENT
Particular expertise is required of the insurer when deter-        In cases of physical damage to the insured contract works,
mining the sum insured. As a rule, the approximate con-            the insurer will indemnify the necessary costs incurred for
tract value at the beginning of the insurance term can             restoring or replacing the damaged contract works. The
serve as a provisional sum insured and is used as the              repair costs will sometimes be higher than the original
basis for calculation of the premium. However, the con-            expenditure up to occurrence of the loss. However, if the
tract value must be regularly reviewed by the insured to           cost types are the same as those included in the sum in-
take account of inflationary price rises or higher sums            sured, they will be indemnified in full. This is not the case
due to supplementary contracts during the construction             with costs which are first incurred during repairs (e.g. re-
period, and this sum insured must then be adjusted cor-            moving damaged parts in order to carry out repairs). The
respondingly in the policy. The sum insured can also be            policies recommended by Munich Re include such costs
increased by a safety margin in order to avoid the danger          only if this has been specifically agreed and a first-loss
of underinsurance. If this margin exceeds the actual sum           sum provided for this purpose.
insured upon completion of the construction work, the              This procedure should be applied above all to cleanup
insured is granted a corresponding premium refund. In              costs (removal of debris) and loss-locating costs. In both
all cases, however, the total sum insured is equal to the          cases, the duty to indemnify depends on whether or not
maximum indemnification for all claims payments. On the            expenditure was incurred in conjunction with an indemni-
other hand, it is not advisable to wait until the end of the       fiable loss. We believe that this procedure allows insurers
construction phase before adjusting the sum insured, as            to assess their liabilities more accurately. And it is also in
experience has shown that the policyholder’s interest in           the interests of the policyholder, who can then decide on
Page 141                                                                                                              5 Insurance

the amount of cover required in view of the potentially           5.1.2 Advance loss of profit insurance
very high “additional loss costs”. The same also applies to
indemnification of additional planning costs which may be         The large proportion of borrowed capital required to fi-
incurred due to repairs if the original planning costs were       nance high-rise construction projects has made principals
not included in the stipulated sum insured or if new plans        increasingly aware that conventional property policies will
are required on account of the circumstances surrounding          only cover a limited part of the overall loss, but not the
the loss. Only those costs will be indemnified which are          loss of operating profit or standing charges due to delayed
necessarily incurred in order to restore the building to the      commissioning or occupancy following a loss.
same technical condition as immediately before occurrence         Even such additional agreements as contractual penalties
of the loss. However, if the original condition is improved       or liquidated damages provide only inadequate relief here.
or changed as a result of the repair, this also means that        For this reason, the existing CAR (EAR) policy can be ex-
any costs associated with such improvement or change              tended by means of an ALOP cover. The purpose of this
will not be indemnifiable. The same applies if other, more        extension of cover is to insure the principal’s financial
complex methods are used for the repairs; they, too, are          losses due to delayed commissioning or occupancy fol-
only indemnifiable to the extent that they were included          lowing an indemnifiable CAR loss during the construction
in the original sum insured. The agreed deductible must           phase.
in all cases be taken into consideration in the calculated
amount of indemnity.                                              FORM OF COVER
                                                                  ALOP risks are written in line with Section III in the
RISK ASSESSMENT                                                   Schedule to the standard policy for property cover. If the
Assessment of the physical hazard by insurers should be           property policy provides for a very large scope of cover,
based on the same considerations as those underlying the          this may have to be reduced to take account of the ALOP
choice of a certain construction method. In addition, how-        cover. This applies particularly to the exclusion of losses
ever, they must also consider, for example, whether a cer-        following delayed completion of the construction work as
tain method or material was perhaps only selected in              a result of earthquakes.
order to save time or money. The insurers must then               Stand-alone ALOP covers without property insurance
determine whether, in the light of known risk factors, a          should as a rule be declined because, when it comes to
higher risk of physical damage was knowingly accepted by          adjusting property losses, the necessary information is
the principal or contractor as a result of this choice.           lacking and there is no way to influence the adjustment
Assessment of the moral hazard always begins with the             process.
planning process. The manner in which the planning has
been organized must be reviewed; for instance, to deter-          POLICYHOLDER
mine whether principals assign the planning and super-            Since ALOP covers exclusively protect interests of the
vision of the construction work to their own office or            principal, the latter should be the sole beneficiary. In order
whether they retain various engineering offices for this          to ensure that they are able to exert their full influence in
purpose. The question whether planning and execution              the event of a loss, however, both the principal and the
were done under time pressure and whether the schedule            contractor should be named as policyholders in the basic
allowed for adequate time buffers can also be of decisive         policy cover.
importance. Last but not least, the contractors’ experience       Contractors on the other hand cannot obtain ALOP cover
on similar high-rise construction projects, and particularly      to insure their consequential losses – above and beyond
the quality of the contractors’ construction or erection per-     the property losses covered by Section I of the CAR policy
sonnel, can also be of great importance when assessing            – such as penalties, interest due on withheld warranty
the moral hazard.                                                 sums and other “soft costs”.
                                                                  Banks should also be excluded as policyholders, since
EXTENDED COVERS                                                   their interests should be regulated in the financing agree-
The CAR policy can be suitably extended with the aid              ments concluded with the principal, independent of the
of various other standard clauses, including those applic-        terms and conditions of insurance.
able to EAR insurance, in order to provide sufficiently           A special situation only arises in conjunction with the in-
comprehensive cover for the erection work concerned.              creasingly widespread “build-operate-transfer” (BOT)
The following most commonly used clauses provide                  projects where principal and contractor act together and
extended cover for political risks (Clause 001), cross            therefore are joint usufructuaries of the building following
liability (002), extended maintenance (004), overtime (006),      its completion. In such a case, they are both named policy-
airfreight (007), fire-fighting facilities (112) and designer’s   holders under the ALOP cover, but with due regard to the
risk (115).                                                       possibility of a higher moral hazard.
5 Insurance                                                                                                                Page 142

SUM INSURED                                                       The policy recommended by Munich Re for this cover pro-
The sum insured is normally equal to the gross annual             vides for a one-off application of the time excess, since
profit, i.e. projected fixed costs and operating profit for the   numerous cases of physical damage during the construc-
high-rise building. This gross profit is determined by de-        tion period will ultimately delay commissioning of the
ducting the variable costs from the sales or profit. Insur-       high-rise building, thus resulting in only one ALOP loss
ance is not required for these variable costs (e.g. cost of       during the agreed indemnity period.
electricity, water, personnel), since they are not yet in-
curred when the delay occurs.                                     CLAIMS HANDLING
However, the principal’s possible losses are not limited          The handling of claims, i.e. determination of the indemnifi-
solely to the lost profit from letting or leasing the             able period of delay in completing the building and the
high-rise building. The following can therefore also be           resultant loss of profit is normally complex and time-con-
insured:                                                          suming. For this reason, progress should be verified at
– “Ongoing rent costs” if the policyholder must pay rent          regular intervals during the construction phase, so that
  for continued occupancy of other business premises              loss-related delays can be distinguished from those un-
  when completion of the new high-rise building is                related to losses and so that their impact on the original
  delayed, since he or his tenants cannot move into the           completion date can be traced.
  new premises on schedule.                                       So-called one-off costs cannot be insured, i.e. sums which
– “Ongoing interest charges” incurred by the principal if         are due for payment or which are lost in full on a fixed
  he cannot sell the building at the planned time and             date, such as tax benefits, seasonal business, lost orders
  must repay the loans taken out to finance construction          and licences.
  of the building or if the interest due cannot be paid at
  the planned time out of income from rental or leasing.          5.1.3 Insurance of contractors’ plant and machinery
– “Additional costs” if the loss of profit can be avoided
  or reduced in this way, for instance by purchasing              Construction plant and machinery can be insured under
  outside electricity, renting flats, office or computer          the CAR policy, through Clause 202 in the EAR policy or in
  capacities.                                                     a completely separate contractors’ plant and machinery in-
                                                                  surance. The scope of cover is the same in all three cases.
Loss-minimization expenditure will also be indemnified up         Basically, this concerns machinery insurance for contract-
to the value of the indemnifiable loss of profit which has        ors and is limited to external causes of loss. In other
been avoided in this way.                                         words, the insurance does not cover losses due to internal
If the agreed period of indemnity exceeds one year, the           mechanical or electrical problems.
projected sum insured for the entire indemnity period             In high-rise construction, such machinery and plant is re-
must also be specified in addition to the one-year sum            quired above all for the retaining walls, foundation struc-
insured.                                                          tures and excavation. Cranes are used for construction of
                                                                  the high-rise building as such. However, care should be
PERIOD OF INDEMNITY                                               taken to ensure that all the plant and machinery is insured
The maximum period of indemnity to be specified in the            and not just such highly exposed plant as cranes and scaf-
policy should be sufficient to allow damaged or destroyed         folding. The sum insured should correspond to the re-
parts of the building to be repaired or replaced. Due to the      placement value of the insured machinery and plant, since
difficulties often encountered in removing rubble and in          this is the only value that can be objectively determined;
obtaining new licences, this can easily result in indemnity       in the case of partial losses – which make up the bulk of
periods considerably longer than the originally planned           all losses – the repair costs can then be indemnified new-
construction period.                                              for-old without deduction. It is only with the much less
                                                                  common total losses that the amount of indemnity is
EXCESS                                                            limited to the current value.
Time excess is always preferable to monetary excess with          Experience has shown that numerous individual losses
this form of cover and should be equal to at least four           must be expected in particular when insuring contractors’
weeks per twelve months of construction time. In view of          plant and machinery. Appropriate deductibles can there-
the long time required for the construction of high-rise          fore reduce not only the claims burden, but also claims-
buildings, this results in a highly desirable time excess of      handling costs, while at the same time creating an incen-
several months.                                                   tive for the policyholder to prevent losses and ensure the
                                                                  orderly organization of construction work.

                                                                                        86 HEAVY PLANT IN USE DURING FOUNDATION WORK
5 Insurance                                                                                                           Page 144

5.1.4 Decennial liability insurance                             This basic cover is normally extended accordingly with
                                                                additional inclusions in line with individual requirements,
This special form of cover for buildings originated in          such as
France. In accordance with the Napoleonic Code, all build-      – natural hazards: earthquakes, floods, windstorm, land-
ings are insured against total or partial collapse for a          slides, hail, volcanic activity, snow pressure, avalanches;
period of ten years (hence the term “decennial”) following      – political risks: strikes, riots and civil commotion, sabo-
their completion, provided that the loss is attributable to a     tage, possibly terrorism;
defect or fault in the performance of one of the parties        – other perils: impact of vehicles, water damage, sprinkler
involved in construction during the construction phase.           leaks, glass breakage, malicious damage, graffiti.
This form of long-term cover has only become established
in a few markets and is normally limited to buildings,          ALL-RISKS POLICIES
including high-rise buildings. The scope of cover varies.       Policyholders in a number of markets are increasingly de-
The commonest extended cover includes leaks in under-           manding all-risks policies for high-rise buildings as well.
ground levels, facades and the roof, which can prove            This form of cover includes all of the risks under one pol-
problematical due to the frequently unknown long-term           icy which are not explicitly excluded.
performance of seals and the highly complex, cost-inten-        Although these policies offer the policyholder extensive
sive repairs.                                                   insurance cover, they must be examined with particular
                                                                care by the underwriter. Calculation of the premiums is no
A distinction is made between countries, such as France,        longer transparent in these cases, since the extensive
in which this cover is obligatory and markets which only        scope of cover may tend to “veil” the insured perils.
offer this form of cover in isolated cases.                     A distinction must also be made from one country to the
Technical inspection of the construction work by an inde-       next with regard to the scope of liability. Such political
pendent inspection agency or engineering office is nor-         risks as terrorism and sabotage, for instance, may be in-
mally essential before decennial liability cover can be         cluded in an all-risks policy without additional premium in
granted. The availability of such cover is dependent on         some countries, but excluded from the standard cover in
this agency or office having submitted a satisfactory final     others on account of local claims experience.
report stating that it has no reservations as regards the       Inclusions from non-property classes, such as third-party
stability of the high-rise building.                            liability and machinery breakdown insurance, are also in-
The principal is the insured party and also beneficiary in      creasingly to be found in all-risks covers.
the event of a loss. However, the insurer can also seek         The owner of a high-rise building and its users or tenants
recourse from contractors, subcontractors and suppliers         are frequently separate and distinct legal entities with dif-
if they can be held liable for the loss.                        ferent policyholders, i.e. the owner for the building as
Due to the long period of liability, insurers must make ade-    such and the tenant for its contents and furnishings. For
quate provisions with regard to administration and when         the insurer, this may result in exposure to accumulation,
carrying forward reserves.                                      which must be taken into account accordingly. Depending
                                                                on the purpose for which the building is used by its ten-
5.1.5 Insurance of buildings, fire insurance                    ants, e.g. offices, computer centre, flats, hotels, possibly
                                                                also commercial businesses (multi-occupancy building),
For property insurers, insurance of high-rise buildings         the loss exposure can be quite substantial.
is nothing unusual in terms of designing the policy. As in
the case of “normal” buildings, the policy is designed          In conclusion, from the insurer’s point of view high-rise
along the lines of industrial or commercial insurance for       buildings are exposed to the same risks as other residen-
buildings and sometimes also of insurance for residential       tial and/or office buildings as far as the scope of cover is
buildings.                                                      concerned; for this reason, they are not different from
A distinction is merely made between two essential forms        other risk groups with regard to insurability. Only the spe-
of cover:                                                       cial characteristics of certain risk situations have a limited
                                                                influence on pricing (see PML, loss prevention). The pos-
NAMED-PERILS COVER                                              sibility of accumulation must be taken into account, how-
The model of named-perils cover is derived from the basic       ever, when the building and its contents are insured separ-
perils of fire, lightning strikes, explosions and crashes by    ately.
manned flying objects or parts thereof or of their cargo.       The policyholder’s primary interest is to obtain the most
This form of cover allows the insurer a very good over-         extensive insurance cover possible in return for a premium
view of the perils to be covered and ensures the trans-         commensurate with the risk.
parency necessary for fixing prices.
Page 145                                                                                                           5 Insurance

5.1.6 Loss of profit insurance                          Additional costs

Standard covers or customized insurance (on request)             On the other hand, it is also perfectly possible that if a
are offered for the loss of profit risks mentioned in            business is favourably and strategically located in the
Section 4.9.                                                     high-rise building, the tenants may have decided on a
                                                                 long-term investment by concluding a lease over several Loss of rent                                             years in order to protect their interests. The following
                                                                 circumstances may have to be taken into account:
The high-rise building owner’s interest in steady income         – The rental value of the premises at the time of the loss,
from rent is normally protected through loss-of-rent insur-         and probably throughout the remaining term of the
ance. In accordance with the applicable General Terms               lease, is appreciably higher than the rent actually paid,
and Conditions of Insurance (ABM 89), insurers in Ger-              with the result that the tenant must expect to pay more
many will indemnify the insured loss of rent for the build-         in order to rent comparable premises elsewhere.
ing specified in the insurance contract, as well as for other    – Advance payments of the rent which have not yet been
parts of the property which have been destroyed or dam-             amortized and which, under the terms of the lease, need
aged by specified perils. Where rented property has been            not be refunded in the event of a loss.
destroyed or damaged, tenants are entitled by law or             – Improvements in the value of permanent fixtures and
under the lease to refuse payment of part or all of the rent.       fittings which have been financed by the tenant, but
The value insured is normally equal to the value of one             which have not yet been amortized and which, accord-
year’s rent and the sum of ongoing ancillary costs for a            ing to statutory regulations, he cannot remove when
period of one year.                                                 vacating the premises following a loss.
The loss of rent will be indemnified, at most, until the         – Under the terms of the lease, the tenant is obliged to
premises are reusable, regardless of official restrictions on       continue payment of all or part of the rent although the
restoration. If the tenancy ends on account of the damage           premises cannot be used on account of the loss.
and if the premises cannot be relet when restored even if        American insurers offer “leasehold interest coverage” to
due care and diligence have been exercised, then the loss        cover such eventualities. European insurers offering loss
of rent will be indemnified after this time until the prem-      of profit insurance will indemnify the additional costs in-
ises have been relet, but at most for three months. Unless       curred to minimize the impending insured loss.
otherwise agreed, loss of rent is indemnified for a max-
imum of twelve months as from occurrence of the insured Contingency planning
On Anglo-Saxon markets loss of rent can generally be             The more exposed a skyscraper’s position as a regional
covered as a supplementary item under insurance of               attraction and the more special the fixtures and fittings in
buildings. However, coverage ends when the rooms are             the rented premises, the greater the business-interruption
finally restored, i.e. reusable, regardless of any further       risk, for it will probably be very difficult and exceedingly
loss of rent until a new tenant can be found.                    expensive to relocate business operations to suitable alter-
In such cases, the owners of high-rise buildings of the          native premises.
type described here are advised to take out loss of profit       The survival of a company may often depend on detailed
insurance corresponding precisely with the terms of the          and regular reviews to assess the feasibility of such con-
lease. This applies in particular to the period of indemnity     tingency plans which would be triggered by a potentially
until the entire establishment has been economically re-         catastrophic loss.
habilitated; agreements with terms of up to ten years are        Although loss of profit insurance can indemnify financial
therefore entirely possible. Another advantage of loss of        expenditure for a calculated period of time, it cannot
profit insurance is that it covers all additional costs, inso-   compensate for the loss of contact with key customers,
far as they actually reduce the threatened loss of rent.         a situation which could easily be averted by adequate
Such costs include, for example, additional expenditure          contingency planning. The results of such perfect planning
for short-term emergency repairs, overtime for contract-         were demonstrated following the bomb attacks on the
ors’ employees and other trades, as well as special ad-          Commercial Union building in London on 10th April 1992
vertising measures taken to find new tenants.                    and the World Trade Center in New York in February 1993.

                                                        Prevention of access

                                                                 Loss of profit insurance (business interruption, additional
                                                                 costs, etc.) can be extended to cover other risks, including
                                                                 the risk of a company being dependent on external oper-
                                                                 ations, institutions and special circumstances.
                                                                 Physical damage on the underground levels (garages) or
                                                                 approach roads to a high-rise building due to fire, explo-
                                                                 sion, earthquake or flooding can lead to at least temporary
                                                                 closure of the entire building complex. Although the
Page 147                                                                                                              5 Insurance

offices, shops, etc., have not suffered any property loss       losses should only be included if the designer and site
as such, they can expect profits to be affected in different    manager have no interests in the widest possible sense in
ways – unless they have appropriate insurance (preven-          the delivery, erection and execution of the work. Such in-
tion-of-access insurance). American standard policies           dependence is only feasible with freelance engineering of-
permit claims for damages for up to two weeks in such           fices which have no financial or personnel links to the con-
cases.                                                          tracting companies and suppliers. Only then is it possible
                                                                to distinguish between a claim for damages based on fault
                                                                on the one hand and a claim for performance and war-
                                                                ranty, which is not covered by the liability policy, on the
                                                                other. This condition is not met, for example, by engineer-
5.2 Third-party liability insurance                             ing offices which act as general contractor. In such cases,
                                                                the liability policy should be limited to the second essen-
As can be seen from what has been said so far, third-party      tial scope of cover, namely third-party losses (bodily injury
liability risks are also to be expected during the construc-    and physical losses). The term of the object policy general-
tion of high-rise buildings.                                    ly covers the planning and construction phase up to final
A distinction must be made between liability risks during       acceptance of the construction work with a period of sec-
planning and construction and those during occupancy of         ondary liability of between two and five years as agreed.
the high-rise building. The product liability risk of the
manufacturers of the individual construction elements will      RISK ASSESSMENT
not be discussed further here.                                  Every high-rise building could be considered a prototype
The high technical requirements to which engineers and          on account of such different parameters as location,
contractors are subject in the construction of a high-rise      height, intended use, choice of materials and natural haz-
building naturally also pose a special challenge for the        ards. Particularly high standards are therefore imposed
liability insurer in terms of recording, assessing and          with regard to the skill and experience of the planning en-
underwriting such risks.                                        gineer. Technical know-how is also required of the liability
                                                                insurer so that these difficult planning risks can be as-
5.2.1 Insurance of the designer’s risk                          sessed and rated. The following criteria in particular must
                                                                be taken into account when assessing the risk:
A planning engineer or office can obtain professional in-       – Qualifications and experience of the policyholder
demnity insurance to cover the liability risks associated       – Number of partners and number of engineers involved
with planning and site management.                                in the project
In the case of larger projects, a customized property policy    – Total fees
is advisable with correspondingly higher limits of indem-       – Contract price
nity which should also be available separately, instead of      – Responsibilities and liabilities accepted
an annual policy for twelve consecutive months.                 – Construction method applied (Does it reflect the latest
                                                                  scientific and technical findings? Have any comparable
SCOPE OF COVER                                                    projects already been completed?)
The scope of cover under professional indemnity insur-          – Particular geological conditions, groundwater conditions
ance for civil engineers basically corresponds to the             and natural hazards to be taken into account in the plan-
generally applicable professional indemnity insurance for         ning (earthquakes, wind, possibly floods)
architects and construction engineers.                          – Surrounding area (e.g. closely built-up city centres, pub-
Insurance cover is provided for all statutory claims for          lic roads: damage due to falling parts)
damages from errors and omissions by the insured in the         – Planning period
discharge of his precisely defined responsibilities.            – Particular circumstances aggravating the risk (e.g. use of
The geological conditions on site play an important part          new materials, facade elements)
on account of the considerable load concentrations. If soil     – Effect of construction work on the neighbourhood
analyses are performed by the designing engineer himself          (shadows, poor television reception, noise)
or if he is contractually responsible for selecting, employ-
ing and possibly supervising a geologist, then he may be        5.2.2 Insurance of the construction risk
liable for the consequences of inadequate soil analyses as
well as for incorrect soil analyses during the planning         The specific liability risk of the contractor responsible for
phase.                                                          construction of a high-rise building lies firstly in the risk of
                                                                injury to his own employees (employers’ liability). This
The most important scope of cover relates to the so-called      particular risk of bodily injury is due to the fact that the
object loss, i.e. loss or damage to the high-rise building as   workers often have to work at dizzying heights and if a fire
such, insofar as such loss or damage is attributable to an      breaks out in the high-rise building, the number of casual-
error for which the planner is responsible. However, object     ties and fatalities is likely to be very high.

5 Insurance                                                                                                              Page 148

Secondly, the risks depend on the location of the high-rise       What are the problems associated with an insurance
building, as it will normally be located in a city centre,        solution employing a common project policy for all con-
with dense traffic and narrow streets. Falling parts or           tractors involved in the construction work? Since the prin-
crashing scaffolding and cranes can cause physical dam-           cipal is the policyholder and some of the principal’s claims
age to nearby main traffic arteries (urban motorway,              against contractors/designers are also included in the
tramways, railway lines) or to adjacent buildings, as well        insurance, this means that there is – at least formally –
as bodily injury to road/rail users and local residents.          a certain degree of cover for first-party losses. In practice,
Interruptions to traffic can lead to consequential finan-         however, the problem is mitigated by the surplus function
cial losses. This highlights the particular risk of a major       in that claims for damages are first examined and, where
loss during the construction phase of a high-rise build-          justified, also settled by the insurers of the mutually inde-
ing.                                                              pendent basic covers. Indemnity under the project policy
Moreover, the extensive foundation work and construction          would only kick in thereafter.
of the underground levels make it necessary to excavate           CAR or EAR policies include the possibility of insuring
deep pits, which often reach below the groundwater table.         the third-party liability risk of all contractors involved in
Depending on the type of retaining wall used, it may also         the construction work under Section II. In both policies,
be necessary to lower the groundwater table. The risk of          however, the indemnity limits of the third-party liability in-
subsidence, ground motion and even shear failures result-         surance section are subject to certain limitations. An add-
ing from such work must be assessed with particular care          itional third-party liability policy known as the contractors’
due to the risk of major losses.                                  excess liability (CEL) policy can be concluded if higher in-
                                                                  demnity limits are desired, as may be assumed for high-
SCOPE OF COVER                                                    rise construction, for instance on account of the particular-
The normal limits of indemnity are usually insufficient for       ly exposed nature of the risk.
such major projects or particularly exposed risks. Two al-
ternatives can be chosen in such cases: either the limit of       RISK ASSESSMENT
indemnity in the annual policy is increased for the particu-      When assessing the risk, it is important to appraise the
lar object in return for a correspondingly higher premium         potential degree of bodily injury losses within the frame-
or separate liability insurance is concluded, tailored to the     work of employers’ liability and particularly the possible
individual project in question. For the insured, the latter al-   third-party losses to the direct surrounding area as a
ternative has the advantage that this limit of indemnity is       result of falling parts, tools or even partial collapse of the
available exclusively for this one project, thus eliminating      high-rise building. Damage to adjacent buildings as a re-
the risk of limits in the annual policy being exhausted by        sult of lowering the groundwater table or damage due to
losses on other projects.                                         ground motion as a result of piledriving, underpinning
                                                                  and driving underpasses can often prove more expensive.
However, there is also another possible variation: high-rise      The following aspects must be taken into account in par-
construction involves not only the general contractor, but        ticular:
also numerous other contractors (main and ancillary con-          – Contract price
struction trades). In order to obtain uniform and adequate        – Number of site employees and total payroll
insurance cover for all contractors, large or small, it is        – Responsibilities and liability accepted
standard practice for all companies to agree on a single          – Construction methods and schedule
policy with a uniform limit of indemnity.                         – Location, surrounding area, neighbourhood
The policyholder is frequently the principal who takes out        – Particular geological conditions
the policy on behalf of the contractors (third-party ac-          – Lowering of the groundwater table, blasting, underpin-
count); the latter are then deemed to be insured persons.            ning, driving underpasses
From the insurance point of view, they are treated as if          – Contractor’s experience
they each had their own policy. However, it is also stand-        – Construction period, maintenance period, period of
ard practice to agree that the individual companies must             secondary liability
take out their own liability insurance with certain minimum
limits and that this liability insurance takes precedence         5.2.3 Insurance of the operational risk
over the joint project policy. The project policy thus takes
the form of a surplus cover.                                      When the construction work is complete and the high-rise
The principal’s risk can also be included from the outset.        building has finally been taken into service, it is taken over
Cover is occasionally also extended to include the risk of        by the operator or principal, who is consequently respon-
independent planners (property loss and third-party liabil-       sible for all losses suffered by third parties through the
ity), albeit usually with considerably lower indemnity            operation of the high-rise building. This operational risk
limits and, analogous to the procedure outlined above             would be covered by the usual insurance for homeowners
for the contracting companies, only subsidiary to higher-         and property owners: it protects the owner in his capacity
ranking basic covers.                                             as owner and lessor of the high-rise building.
Page 149                                                                                                          5 Insurance

The main risk lies inside the building, particularly if it is   5.3.3 Operating phase
open to the public. The most commonly occurring losses
will be personal accidents on improperly serviced stairs or     From an underwriting point of view, the fire PML is the
elevators and bodily injury due to falling objects. However,    most important element during operation of a high-rise
the owner is only liable for causes within his sphere of re-    building. The PML for a given risk refers to the probable
sponsibility. These include regular servicing and mainten-      maximum loss which must be expected if the event oc-
ance of elevators, safety and control facilities, as well as    curs, with due regard to the conditions surrounding the
compliance with statutory regulations or official require-      risk and based on conservative estimates.
ments (e.g. fire protection). For this reason, the relevant     When estimating the PML of “normal” risks, we base our
maintenance, safety and fire-protection schedules, as well      assessments on complexes, but this is not possible in the
as fire procedures should be inspected by the insurer           case of high-rise buildings, as they usually comprise only
when underwriting a third-party liability policy for the        one complex. What is important, however, is that we –
owner and lessor of a high-rise building.                       unlike many other companies – do not take account of the
The premium is normally calculated on the basis of the          existing fire-protection facilities and precautions in our
gross annual rent value, i.e. the total income from rent.       PML estimate. The following are disregarded in particular:
                                                                – Manual and automatic fire detection systems
                                                                – Fire-extinguishing equipment, such as wall hydrants,
                                                                   sprinkler systems, CO2 or inert-gas fire-extinguishing
5.3 Problem of maximum loss                                     – Efficiency of the fire brigade
                                                                These points are not considered to be factors which re-
Due to the high concentration of values, the probable           duce the PML because they occasionally fail when the in-
maximum loss (PML) must be estimated separately for             sured event occurs. Structural fire-protection measures,
each of the risk phases, also in the case of a high-rise        such as fire-resistant construction practice, fire-resistant
building.                                                       sealing and fire compartments (see Section,
                                                                on the other hand, can be considered as PML-reducing
5.3.1 Construction phase                                        factors.
                                                                Experience has shown that the total loss of a high-rise
As is usual for all major projects, the PML estimate should     building is highly improbable, so that an assumed PML of
be based on a separate assessment of the risk. In the case      100% should remain the exception. Although fires result-
of high-rise buildings, fire will normally be considered a      ing in total demolition of the high-rise building are known
peril relevant to the risk and therefore form the basis for     to have occurred (see Section 4.2.3), this was essentially
the PML estimate.                                               due to other reasons and not primarily to the impossibility
The measures required for active and passive fire protec-       of repair. Moreover, the total sum insured was not paid as
tion should not lead to any reduction in the PML, since         indemnification in these cases.
some of these measures only become fully effective when         On the other hand, we do not believe that it is right to
the building is finished.                                       specify flat-rate percentages of the sum insured as the
This explains why fixed percentages are not specified           PML for high-rise buildings, nor to define a certain number
here; at best, a deduction for the often extensive and ex-      of floors as determining the PML, as is sometimes done.
pensive foundation measures can be justified when as-           We believe that an individual approach is required which
sessing the parts at risk, since these foundation measures      takes into account the following criteria:
are not exposed to fire.                                        – Form of the building
Depending on local conditions, exposure to windstorm,           – Construction practice
earthquakes and natural hazards may also be of relevance        – Internal layout
for the PML estimate during the construction phase.             – Facade design
                                                                High-rise buildings are frequently erected on a podium
5.3.2 Decennial liability insurance                             with one or more levels. When estimating the PML, it is
                                                                important to establish whether a fire breaking out in the
The same considerations basically also apply to decennial       podium can spread to the rest of building or whether this
liability insurance, except that here fire is replaced by the   is prevented by protected fire-resistant separations. Three
fairly rare risk of collapse. With major projects, it may       forms of building must be taken into account here:
also be advisable in view of the limited capacity available     – small dot-like layout/towering building,
worldwide to introduce a limit of indemnity in order to         – flat slice-like building (length of the building equals at
facilitate placement of the risk.                                  least three times its width),
                                                                – large sprawling layout (base area in square metres
                                                                   equals at least 50 times the height of the building in
5 Insurance                                                                                                            Page 152

The probability that entire floors will be gutted by fire is     So far, we have only considered the building as such. Its
highest in the case of the first group of buildings.             contents are normally insured separately, the policyhold-
With the second group, subdivision into fire compart-            ers usually being the building’s users or tenants. If the
ments is more likely, if only on account of statutory re-        building is insured together with its contents, the PML for
quirements with regard to the length of rescue routes. If        the contents must be taken as a cumulative figure when
the partition walls have been correctly designed and di-         estimating the PML. Contents require similar consideration
mensioned, a lower percentage loss may therefore be              to interior finishings. Once again, special attention must
assumed per floor.                                               be paid to “multi-occupancy buildings” (see Section 5.1.5).
An even larger number of fire compartments is to be ex-          How appropriate is it to specify a terrorism PML for high-
pected with the third group of buildings, and this should        rise buildings? In our point of view, there is little point in
reduce the loss per floor still further. Going purely by the     specifying such a PML, as we would not like to consider
form of the building, the percentage PML must be highest         terrorism a “probable” event. Moreover, it is impossible to
in the first and lowest in the third group.                      give any precise estimate of a loss due to terrorism and
Regardless of the form of the building, the combustibility       the PML would always have to be set at 100%.
of the materials used and the fire-resistance period of the      A bomb attack is the most effective terrorist attack. It is
parts must also be considered. The characteristics of the        perfectly conceivable that trained experts, such as special-
supporting structure and of floors as well as the fire-resist-   ists in the use of explosives, could be used for the “most
ant elements protecting the openings to stairwells and ele-      effective” result. After surveying the building, such spe-
vator or service shafts are important in this respect. The       cialists can easily position their bomb or bombs in such a
facade design is a very important factor for vertical propa-     way that it will cause the entire building to collapse.
gation of the fire and consequently for the PML. A fire          What is more likely, however, is that a car bomb contain-
must be expected to spread from one floor to the next if         ing a large charge of explosives will be detonated in an
the window glazing is not fire-resistant and if the flashover    underground car park or in the immediate vicinity of the
distance between the windows on consecutive floors is            high-rise building. The extent of the destruction is conse-
too short.                                                       quently a matter of chance and therefore hard to estimate.
The risk of fire spreading is even more serious if the build-    It is necessary to adopt a country-specific approach to this
ing includes an atrium, since the resultant chimney effect       issue, also taking account of the building’s location and
also has to be considered.                                       occupancy. An office block in an industrial complex will
When estimating the PML, it is useful to consider the            undoubtedly be a less likely target for terrorists than a
building’s supporting structure and its finishings separate-     city-centre office tower. There have been sufficient ex-
ly. The finishing work must be taken to include all non-         amples of such cases in the recent past.
bearing inner and outer walls including panelling, all           If cover for terrorism cannot be excluded for reasons of
building service installations and elevators, all doors, win-    market policy in a country with high exposure to terror-
dows, floor coverings and ceilings.                              ism, then it is perfectly appropriate to assess the PML at
In the past, it was common to do a 50:50 split on support-       100% of the sum insured.
ing structure and finishings, but this ratio has now             Earthquake exposure must also be taken into account for
changed to 30:70 on account of the more complex build-           the PML during the operational phase. The major earth-
ing services and more extensive wiring in modern build-          quakes experienced in recent years caused such extensive
ings. Experience has shown that considerably less than           damage to high-rise buildings as to make repair impos-
50% of the supporting structure of a high-rise building will     sible (Mexico City, Kobe). Older buildings and particularly
be damaged by fire, depending on its type, particularly          buildings with “soft storeys” (see Section 4.4) were worst
as regards its fire resistance. In the case of the finishings,   affected.
on the other hand, the loss must be expected to be in the        When estimating the earthquake PML in regions exposed
region of 40–100% due, among other things, to damage             to this risk, it is therefore important to establish whether
caused by smoke and fire-fighting water.                         modern anti-seismic construction codes exist and whether
The highest percentage losses are suffered by the support-       they were also applied to the high-rise building under con-
ing structure and finishings in the first group of buildings     sideration. If these construction codes are known to have
and the lowest by those of the third group. What has been        been violated or if there are any doubts in respect of com-
said above must be considered one possible approach for          pliance, then a PML of 100% should also be assumed for
estimating the PML and not as an algorithm, since numer-         earthquakes.
ous different criteria must be taken into account separately     The same applies to windstorm, volcanic activity and
in each case.                                                    other natural hazards in regions exposed to these particu-
In addition, such covered items as cleanup and demolition        lar risks.
costs, increased costs of working due to conditions im-
posed by the authorities and price rises during the restor-      5.3.4 Accumulation control
ation period, must be added to the PML. These are normal-
ly first-loss risk items which should be included 100%.          This problem must be considered above all in conjunction
                                                                 with the perils windstorm, earthquake and fire primarily in
                                                                 respect of buildings covered by CAR, EAR or fire policies.
Page 153                                                                                                             5 Insurance

This naturally only applies to areas or cities with a corres-   specified here on account of the considerable scope for
ponding concentration of values in the property insurers’       variation and additional, highly commercial influences pre-
portfolios.                                                     vailing in the various markets.
Munich Re has already stated its views on this subject in a     Where the deductible is concerned, difficult soil conditions
number of publications; it has also drawn attention to the      and the exposure to windstorm due to structural reasons
need for accumulation control and issued corresponding          or progress in construction must also be taken into ac-
explanations.                                                   count in addition to the long time frequently required for
As far as the natural hazards windstorm, earthquake and         the construction work.
flooding are concerned, the values currently at risk in the     If necessary, it must be possible to calculate the risk by
respective exposure zones or specific catastrophe scen-         including suitable special terms, limits of indemnity or
arios are determined using computer-aided data analyses.        exclusions. This applies particularly to high-rise buildings
The respective loss accumulation zones and correspond-          over 500 m, as their exposure to windstorm has not yet
ing loss potential are then determined for these catas-         been sufficiently investigated, and when using inadequately
trophes.                                                        tested materials and construction methods.
We will gladly answer any queries from our clients on
such issues.                                                    5.4.2 Contractors’ plant and machinery

                                                                When determining the premium rate, the number and
                                                                period in use of the highly exposed cranes must be taken
                                                                into account in addition to the scope of cover. Elevators
5.4 Underwriting considerations                                 for transporting materials to great heights are less ex-
                                                                posed to loss, since they are firmly connected to the shell
Different construction methods, different finishings and        on the outside or are located inside the high-rise building.
the exposure to external influences demand careful analy-
sis of the resultant risks. For this reason, only approximate   5.4.3 Decennial liability insurance
rates can be specified for insuring the construction and
operational phases of high-rise buildings, despite the          The level of premium rates for this cover is also largely
availability of statistical analyses extending over many        dependent on the specific market, the market situation
years.                                                          and scope of cover. For this reason, the premium rate can
                                                                range between 5‰ and 15‰ for the ten-year period. In
5.4.1 Contractors’ and erection all risks insurance             addition to the premium, the principal must also bear the
                                                                costs of technical inspections; these costs vary in line with
When determining the premium rate, different degrees of         the size and complexity of the project.
exposure during construction of the high-rise building          The waiver of a deductible is prescribed by law in some
(foundations, structural works, finishing) must be taken        markets; as a rule, however, the long term of this cover
into account in the same way as the proportion of tem-          should be taken into account when determining the
porary auxiliary structures (e.g. retaining walls) and their    amount of excess.
exposure during use. The following documentation
should normally be available:                                   5.4.4 Insurance of buildings, fire insurance
– General drawing and layout plan of the site with an
   overview of the immediate surroundings                       As with all risks, the terms, quality of the risk and price are
– Technical details concerning the construction method,         components which must be taken into account when
   progress made and materials used                             underwriting high-rise buildings.
– Breakdown of the contract price according to the most         Where the terms are concerned and particularly in con-
   important parts (foundations, structural works at under-     junction with the scope of cover, the statements made in
   ground levels/floors above ground, finishing)                Section 5.1.5 apply, with “named perils” and “all risks” as
– Schedule of construction work, particularly in conjunc-       the two main forms of cover.
   tion with regularly recurring natural phenomena (e.g.        All the criteria listed in Section 4.2.4 must be considered in
   monsoon)                                                     order to determine the quality of the risk. Under no circum-
– Expert report on soil conditions                              stances should the underwriter assume that all statutory
– Description of the foundation method, retaining wall,         measures have been taken or that the quality of the risk
   possible lowering of the groundwater table                   is satisfactory simply because of compliance with the
– Layouts, longitudinal and transverse sections of the          regulations. As the cases outlined in Section 4.2.3 have
   building in different planes, details of the most import-    shown, the standard of protection applying when the high-
   ant structural parts (e.g. facade connections).              rise building was erected may well be far below the stand-
The premium rates required for underwriting are deter-          ards required today. It therefore follows that the con-
mined on the basis of an assessment of these documents          struction practice and standard of protection must be con-
and of the structural analyses. Premium rates are not           sidered individually. Particular attention must be paid to
Page 155                                                                                                                5 Insurance

structural fire protection, as well as sprinkler protection       fied in the classes concerned should be decided in accor-
commensurate with the risk.                                       dance with individual requirements.
Although quantitative statements cannot be made, the              In addition, limits of liability also facilitate matters for in-
probability and frequency of a loss occurring and the             surers and reinsurers; liability accumulations can be deter-
amount of loss to be expected will be lower if the quality        mined and updated more easily and precisely. This is par-
of the risk is “good” than in the case of inadequately pro-       ticularly important in countries or regions which are con-
tected buildings. Higher shares can therefore be written in       stantly exposed to natural hazards, such as Japan or Cali-
the case of “good” risks.                                         fornia, where comprehensive insurance cover is provided
In the case of extended basic cover, the risks due to sup-        for a large number of high-rise buildings in an area of in-
plementary perils, e.g. earthquake, windstorm, hail, flood-       tense seismic activity and where there is consequently a
ing, water damage and glass breakage, must naturally              substantial accumulation risk.
also be taken into account in the underwriting. The same          Even in these extreme cases, however, the demand for ad-
also applies to all-risks covers, special attention being de-     equate insurance cover is and was satisfied by insurers
voted to the exclusions (see Section 5.1.5).                      and reinsurers working together as partners. This is par-
General statements cannot be made here with regard to             ticularly true of insurance markets marked by high invest-
the price, i.e. premium rate. Claims experience and local         ment and growth. The benchmark has been raised in
exposure play a vital role in pricing, as do commercial           terms of what insurers require and expect of reinsurers,
considerations. Above all, the premium calculation also           especially with regard to know-how, professional compe-
has to take into account supplementary perils such as             tence, market experience, innovativeness and ultimately
natural hazards and political risks on the basis of individ-      also adequate capacity combined with long-term financial
ual loss exposure.                                                strength.
The quality of the risk is naturally also reflected in the        Munich Re is optimally positioned to meet these chal-
price; in other words, appropriate protective measures or         lenges.
generally “good” quality of the risk will result in a corres-     The lead it has built up globally over the decades in terms
pondingly lower premium rate.                                     of experience and information is based on extensive data-
                                                                  bases. With the help of modern computer-based tools, the
                                                                  latest data can be rapidly made available to the insurers.
                                                                  Comprehensive geo-scientific and underwriting analyses
                                                                  of these data by experts at Munich Re’s head office and in
5.5 Reinsurance                                                   the engineering offices around the world ensure that nat-
                                                                  ural hazards and loss potential can be reliably assessed.
In the majority of cases, there should be no particular           Experienced underwriters are available to our clients at
problems in reinsuring individual high-rise buildings, pro-       more than 45 business units and subsidiaries in our inter-
vided that the necessary conditions have been met for the         national organization, all of which are linked online to the
individual classes (contractors’ all risks, erection all risks,   head office. This enables us to advise prospective clients
insurance of the building, fire insurance, decennial liability    on assessing risk, defining the terms of insurance, and
insurance, third-party liability insurance). On account of        determining and providing the required reinsurance
the different forms of cover, the main thing is to ensure         capacity.
that the policies in question are allocated to the appropri-      During the period of cover, our specialists can actively
ate classes, e.g. engineering insurance, third-party liability    participate in inspections, loss prevention or settlement
insurance and fire insurance (as described in detail in the       of complex losses.
preceding sections) and that the risk is properly assessed        Extensive know-how and the courage to take innovative
in line with the respective policy.                               steps make it possible for our specialists to provide
Special need for reinsurance may arise, however, in the           our clients with professional support in developing new
case of individual major high-rise-building risks and exten-      concepts for cover or new insurance products.
sive accumulation risks resulting from the concentration of       We will gladly answer any queries by our clients, provide
numerous high-rise buildings within a small area. This is         further information or outline possible solutions in con-
indeed the case with skyscrapers of record-breaking               nection with reinsurance and our range of services.
heights and sums insured due to the high fire PML or the
risk of earthquakes or windstorm in areas particularly
prone to such hazards. The need to insure these risks will
normally exceed the capacity of the local insurance mar-
ket. The same also applies with regard to decennial cover
for such risks.
However, even reinsurers with the soundest financial back-
ing cannot accept unlimited liability. In some cases, it will
therefore be necessary to introduce a limit of liability
which makes the risk more manageable and easier to cal-
culate; this will also ensure that the available underwriting
capacity can be fully utilized. The type of limits to be speci-

6 Summary and outlook

Page 157                                                         6 Summary and outlook

The historical and technical development of high-rise
buildings as seen from the point of view of insurers
and reinsurers has been outlined in the individual
sections of this publication. Needless to say, develop-
ment does not stand still, and therefore by the time
this publication appears in print some of the technical
details described here may already have been super-
seded by research, progress and the pressure of costs.

Most of the statements made here, however, will continue
to apply to future high-rise buildings. Despite certain reser-
vations and all economic bottlenecks, the quest to reach
for the sky and erect higher and higher buildings goes on,
particularly in Asia.

For this reason, we as insurers and reinsurers will con-
tinue to devote our attention to these projects in the new
millennium. We are also confident that, thanks to our
worldwide know-how and long-standing experience, we
will be able to offer our clients solutions in line with the
specific risks involved.

    Die Bezeichnung höchstes Bauwerk der Welt bean-
    sprucht zur Zeit der Fernsehturm von Toronto, der neben
    dem Ontariosee 553 m in den Himmel ragt. Das zweit-
    größte Bauwerk ist der Fernsehturm von Moskau mit
    537 m.

    Eine Geschoßflächenzahl von 12 bedeutet, daß die
    Gesamtfläche aller Geschosse über Straßenniveau maxi-
    mal das Zwölffache der Grundstücksfläche betragen
    Bentonit ist ein spezielles Tonmineral, das das Mehr-
    fache seines Gewichts an Wasser absorbieren kann und
    dabei auf das 8–15fache seines Volumens anschwillt.
    Es bildet an den Wänden des Schlitzes eine Schicht,
    wodurch dieser gegen Materialeinbruch stabilisiert wird,
    ohne den Aushubvorgang zu beeinträchtigen.

    Weitere Details sind in unserer Brandschutztafel nach-

    Advance loss of profit.
Picture credits                                                                                                                                                                 Page 158

Page        Picture No.   Title                                                                                   Picture credits

Cover       01            Manhattan, New York                                                                     Image Bank, A. Becker, Anzenberger, Loccisano
  6         02            San Gimignano                                                                           Picture Press, Riedmüller
  7         03            Monadnock Building                                                                      Library of Congress
  9         04            The Tower of Babel                                                                      AKG, Berlin
 10         05            Equitable Life Building                                                                 Museum City of New York
 10         06            Home Insurance Building                                                                 Philipp Holzmann, Frankfurt a. M.
 10/11      07            New York panorama                                                                       Image Bank, A. Becker
 12         08            HongkongBank Headquarters Building, Hong Kong                                           HongkongBank
 12         09            Messeturm, Frankfurt am Main                                                            Werkfoto HOCHTIEF, Essen
 13         10            Petronas Towers, Kuala Lumpur                                                           Munich Re
 15         11            Hong Kong skyline                                                                       Pacific Century, Hong Kong
 16         12            Flatiron Building, New York                                                             Photonica, B. Hubert
 18         13            La Grande Arche, Paris                                                                  Munich Re
 19         14            Canary Wharf, London                                                                    Munich Re
 20         15            Traditional and modern buildings in peaceful co-existence                               Laif, Arthur Selbach
 23         16            Chrysler Building, New York                                                             Image Bank, B. Frommer
 27         17            Details from planning documents                                                         Munich Re
 28         18            Extract from a technical report                                                         Munich Re
 29         19            Opening in an apartment complex                                                         Munich Re, J. Eber
 30         20            Large-bore pile foundation process                                                      Bilfinger & Berger
 30                       Various stages in the diaphragm wall process                                            Bauer Spezialtiefbau, Schrobenhausen
 32/33      21            Diaphragm wall rotary cutter                                                            Bauer Spezialtiefbau, Schrobenhausen
 34         22            Retaining wall to protect neighbouring buildings                                        Munich Re
 34         23            View of a building pit with completed retaining wall                                    Bauer Spezialtiefbau, Schrobenhausen
 36/37      24            Examples of high-rise buildings with steel skeletons                                    Munich Re, A. Kleiner
 38         25            Deformation and bending momentum due to wind with the core construction method          Munich Re
 38         26            Background: Commerzbank Building                                                        Minimax
 39         27            Deformation and bending momentum due to wind with the outrigger truss method            Munich Re
 39         28            Examples of core construction methods and bundled tubes                                 Munich Re
 40         29            Varying load distribution with tubes and bundled tubes                                  Munich Re
 41         30            Example of the arrangement of bundled tubes                                             Munich Re
 41         31            Steel skeleton                                                                          Büro X
 43         32            View from the headquarters building/Headquarters of BMW A. G. in Munich                 Pressestelle BMW A. G., Munich
 44         33            Facade assembly                                                                         Munich Re
 47         34            Ceiling installation                                                                    Top: Munich Re
 47         35            Double flooring                                                                         Bottom: Fa. Mero, Würzburg
 50         36            Elevator in the World Trade Center, New York                                            Visum, Michael Wolf
 51         37            Elevator demonstration by Otis                                                          Left: Otis
 51         38            Maintenance                                                                             Right: Laif, REA/P. Bressard
 52         39            Renovation of a high-rise building                                                      Top: Werkfoto BASF
 52         40            Pile-driving machinery for working in basement floors                                   Bottom: Bauer Spezialtiefbau
 55         41            Petronas Tower                                                                          Munich Re
 56/57      42            Trend towards ever-taller modern high-rise buildings                                    Büro X
 58/59      43            The Millennium Tower – a vision for the 3rd millennium                                  Forster and Partners, London
 60/61      44            Petronas Towers, Kuala Lumpur, Malaysia                                                 Munich Re
 62/63      45            Sears Tower, Chicago                                                                    Anzenberger, G. Sioen
 64/65      46            Empire State Building, New York                                                         Visum, J. Röttger
 66/67      47            Messeturm in Frankfurt am Main                                                          Laif, C. Emmler, P. Langrock
 69         48            Additional heat recovery via piling foundations in the Commerzbank high-rise building   Minimax
 71         49            Fully automated building site                                                           Obayashi Corporation, Japan
 72/73      50            Jin Mao Building                                                                        Shanghai Educational Publishing House
 74/75      51            Shanghai Pudong                                                                         Airphoto International Ltd./Pacific Century Publishers Ltd.
 76/77      52            New York                                                                                Visum, M. Wolf
 76/77      53            China, Guangzhou                                                                        action press, SABA-Laif, REA/Sinopix
 78/79      54            New York                                                                                Image Bank, A. Becker
 80/81      55            New York: view from the World Trade Center                                              Visum, M. Wolf
 82/83      56            New York                                                                                Munich Re, J. Eber
 87         57            Fire in the Broadgate Building, London: sunken roof support beams                       Munich Re
 88         58            Fire-protection information                                                             Munich Re
 90/91      59            Escalator destroyed by fire                                                             Munich Re
 92/93      60            Fire in the Meridien President Tower, Bangkok                                           Munich Re
 94/95      61            Meridien President Tower, increased risk of fire during the final fit-out phase         Munich Re
 96/97      62            Difficult fire-fighting conditions in the Meridien President Tower                      Bangkok Post
 98         63            Combustible waste increases risk of fire                                                Munich Re
100         64            Limited evacuation routes through smoke-filled stairways                                Bangkok Post
101         65            Hong Kong, fire in the Garley Building                                                  South China Morning Post
102         66            Towering inferno                                                                        Munich Re
Page 159                                                                                                                                                                       Picture credits
      Wooden panels on a glass facade destroyed by a car-bomb attack/Interior view of one floor

103             67                    Difficult fire-fighting conditions                                                          Munich Re
106             68                    Special coating on the steel skeleton guaranteeing adequate fire resistance                 Top: HongkongBank, Minimax, Eissing-Kister
106             69                    Fire-detection system in the Messeturm in Frankfurt                                         Bottom: HOCHTIEF/Landis & Gyr
109             70                    Atrium in a bank building                                                                   HongkongBank
112             71                    Dynamic-pressure approaches: effects from friction impact wind speed                        Top: Munich Re, A. Kleiner
112             72                    Typhoon tracks for Japan and California                                                     Bottom: Munich Re
113             73                    Representation of wind impact on a building’s ground-bearing pressure                       Munich Re, A. Kleiner
116             74                    Impact of earthquake loads on the centre of gravity                                         Top: Munich Re, A. Kleiner
116             75                    50 t and/or 90 t heavy dampers                                                              Bottom: Mitsubishi Heavy Industries Ltd.
117             76                    Effective arrangement of dampers in high-rise buildings                                     Mitsubishi Heavy Industries Ltd.
119             77                    Earthquake in Kobe, Japan                                                                   Munich Re
120             78                    Corroded supply lines                                                                       Munich Re, W. Schromm
120             79                    Tension crack in a crosslinked polyethylene pipe                                            Munich Re, W. Schromm
124/125         80                    Blasting of a high-rise office building                                                     Iduna Versicherung
128/129         81                    Interior of a high-rise building following a bomb attack                                    Munich Re, J. Eber
130/131         82                    Wooden panels on a glass facade destroyed by a car-bomb attack/Interior view of one floor   Commercial Union, G. Evans
133             83                    Aircraft debris after a plane ploughed into the Empire State Building                       Associated Press
134             84                    Aircraft crash onto a block of flats in Amsterdam                                           action press, F. Bründel
135             85                    Bomb attack on a federal government building in Oklahoma, USA                               action press, SABA
143             86                    Heavy plant in use during foundation work                                                   Bauer Spezialtiefbau, Schrobenhausen
146             87                    Dangerous workplace                                                                         Laif, REA/Sinopix
150/151         88                    World Trade Center, New York                                                                Laif, P. Gebhard
154             89                    Exterior hoist                                                                              Munich Re

Title                                                         Author                                    Publisher
Architektur des 20. Jahrhunderts                              Gossel/Leuthäuser
Architektur und Städtebau des 20. Jahrhunderts                Lampugnani
Das Hochhaus in Gegenwart und Geschichte                      Goldberger (1984)                         DVA Stuttgart
DIN 1055, Part 4                                                                                        Issue 8/86, 5/89
Elevators and Escalators                                      Strakosch                                 John Wiley & Sons, New York
Erdbebenprognose                                              Geo 3/96
Facility Management 1/95                                                                                Bertelsmann Verlag
Fassadengestaltung                                            Dr. Gartner
Fire Letter No. 24                                            Munich Re
Hongkong, Architekturmuseum Frankfurt a. M.                   Exhibition catalogue (1993–94)            Prestelverlag
La Grande Arche                                                e
                                                              Tˆ te Défense (1990)
Marvels of Engineering                                        National Geographic
Massivbau Vertiefungsvorlesungen                              J. Schlaich                               Universität Stuttgart
Messeturm Frankfurt a. M.                                     Kolodziejczyk                             Technik am Bau (Periodical)
Messeturm Frankfurt a. M.                                     J. Murphy                                 Schriften zur Architektur der Gegenwart
MR Handbook “Water Damage Insurance”                          Munich Re
Preliminary Report on the Northridge Earthquake               WSSI
Schadenspiegel 1/84                                           Munich Re
Schadenspiegel 1/95                                           Munich Re
Schadenspiegel, Special issue 1994                            Munich Re
Skyscrapers                                                   Starrett                                  Charles Scribner's Sons, New York
Special publication “Earthquakes of the Caribbean Plate” Munich Re (1976)
Special publication “Earthquake Mexico ’85”                   Munich Re (1985)
Special publication “Windstorm”                               Munich Re (1990)
The Empire State Building                                     Theodore James, Jr.                       Harper & Row, New York
The Skyscraper Book                                           Giblin                                    T. Y. Crowell, New York
Tuned Active Dampers                                          Mitsubishi Heavy Industries
Wie man Wolken kratzt                                         P. v. Seidlein
Wolkenkratzer – Ästhetik und Konstruktion                     J. Schmidt                                Dumont Verlag

A publication of the Munich Reinsurance Company

© 2000
Münchener Rückversicherungs-Gesellschaft
Address for letters:
D-80791 München
Design: Büro X, Hamburg

Order number 2840-V-e

The paper used for this brochure was produced without chlorine bleaching.

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