Modern aircraft hangars A review of the design trends by wangnianwu

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									                                                                                                                            paper: luke/howson



Modern aircraft hangars:
A review of the design trends
Synopsis                                                           aircraft is also briefly considered.                                 Steven J. Luke
The design, construction and operation of an efficient aircraft
                                                                                                                                        BSc (Hons), MSc,
maintenance hangar probably represents the largest and             Structural materials
                                                                                                                                        CEng, FIStructE,
most important single investment made by an aircraft               The high strength-to-weight ratio of steel makes it ideally suited
                                                                                                                                        FICE, MISWE,
operator with regard to aircraft support services. At the heart    for the modern form of hangar, which normally requires long
                                                                                                                                        MIHKE,
of this is the design process which, when executed properly,       spans and large door openings. It also has the benefit of
                                                                                                                                        Ove Arup & Partners
reduces the one-off cost of construction and optimises the         maximising off-site pre-fabrication and minimising the on-site
                                                                                                                                        Ltd
ongoing organisational and maintenance costs. The design           programme. On the other hand, many successful concrete
itself can be challenging due to the requirements of long clear    hangars have been constructed using reinforced concrete
spans, the necessary provision for substantial loads to be         together with a variety of pre- and post-tensioned elements.         W. Paul
suspended from the roof, airport restrictions on building          Such structures had their heyday in the post-war years up to the     Howson
height and the uncertainty imposed by the need to cater for        early 1970s. The structural forms were principally arches or         BEng, PhD, CEng,
progressively larger aircraft. This paper reviews over 20          balanced cantilevers and were efficient for the significantly        MIStructE, MICE,
different design solutions that have been adopted worldwide        smaller aircraft that were then to be accommodated.                  Cardiff School of
for commercial aircraft hangars that cater for both narrow and        The first integrated 10-bay hangar and workshops to be built      Engineering, Cardiff
wide-bodied aircraft. It identifies useful data and design         in the UK was constructed for British Airways in 1952. The           University
trends, which will benefit the early stages of the structural      complex had door openings of 45m, a hangar depth of 33m, and
frame development.                                                 was set out in two runs separated by a central spine workshop4.
                                                                                                                                        Received: 6/01
                                                                      This was a highly successful in situ and prestressed concrete     Accepted: 3/02
Introduction                                                       building and was followed by a further complex of 10 bays of the     Keywords: hangars,
The first commercial airlines were established in 1939 and today   same size. The latter has now been adapted using external            aircraft, frames, design,
there are approximately 13, 000 narrow bodied (single aisle) and   mobile, rail guided, tail docking enclosures, to allow larger        structural steel,
                                                                                                                                        superstructures,
wide-bodied (double aisle) jets in regular service. Allowing for   aircraft to be maintained (see Fig 2).The earlier hangar complex     prefabrication, beams,
ageing aircraft replacement, Boeing1 and Rolls Royce2 have         was demolished in 1999 to create space for aircraft parking          roofs, suspending
predicted that by 2019 the world fleet of passenger and freight    stands adjacent to a British Airways drive through casualty          equipment, doors,
aircraft will have grown to approximately 31, 755. In compari-     hangar, which can deal with minor maintenance operations             flexibility, fire
                                                                                                                                        protection, cantilever
son, hangar accommodation available world-wide was estimated       around the clock (see Fig 3). Examples of eight international        construction, erecting
by the industry3 in 1993 to be approximately 530 narrow-bodied     projects with concrete frames have been summarised in a paper
and 270 wide-bodied aircraft bays of varying age and condition.    presented at the Airport Forum 19835, which reviews concrete
   The above figures, despite being relatively crude, suggest      hangars constructed between 1960 and 1972.
that there will be a substantial shortfall in hangar accom-           The use of steel in preference to concrete has gained momen-
modation within the next decade. This problem is unlikely to
be solved by merely improving the existing hangar stock. For
example, hangars constructed before 1970 are likely to be of
a modest span, up to 45m, and mainly used for small to
medium narrow-bodied aircraft such as the B737, B757, A310
and A320. Although many of these older hangars have been
converted to accommodate larger aircraft by constructing a
high tail bay extension, (see Fig 1) or by using external mobile
tail boxes (see Fig 2), their further extension to cater for the
next generation of larger aircraft is likely to compromise the
efficiency of the maintenance process. Even the newer
hangars risk losing their commercial viability if they are not
sufficiently flexible to incorporate ‘state of the art’ mainte-
nance procedures, since the demand for efficiency in the
design of aircraft is now being matched by the need to
minimise aircraft maintenance cycle time in order to
maximise revenue. As a result, the hangar is no longer consid-
ered a ‘shed’ but a vital extension of the high technology
process necessary to support efficient maintenance opera-
tions.
   This paper reviews the development of modern aircraft
hangars and identifies design trends and other information                                                                              Fig 1. (above)
which will be helpful in the preliminary design of the struc-                                                                           Quantas 96 high bay
tural frame. This has been achieved by synthesising an                                                                                  hangar extension,
extensive literature survey with information obtained from                                                                              Sydney, 1989
visits to existing aircraft maintenance bases together with
personal experience of the design of large hangars and the
development of facility plans for major installations.
Significantly, it identifies several families of structures that
are most commonly used for existing hangar facilities and
indicates the range of the structural steel weights for the
superstructure systems. Other information is also presented                                                                             Fig 2. (left)
relating to the primary constraints needed to establish these                                                                           British Airways tail
client requirements that significantly influence the design of                                                                          docking mobile
the frame. The likely impact of the next generation of larger                                                                           structures, LHR

                                                                                                              6 August 2002 – The Structural Engineer|23
 paper: luke/howson


                                                                                                Hangar usage
                                                                                                Hangar buildings have traditionally been rectangular and
                                                                                                framed in many ways to generate a simple building plan.
                                                                                                However, some have adopted the ‘tight fit’ minimum footprint or
                                                                                                ‘triangular shape’ to minimise land-take and building costs.
                                                                                                (Refer to the alternative hangar footprint arrangements illus-
                                                                                                trated in Fig 4). The approach can reduce the building volume
                                                                                                by as much as 25% and consequently heating costs. Minimising
                                                                                                the building footprint will also mean that the available space for
                                                                                                storage and wing tip clearances will be reduced. This aspect
                                                                                                must be investigated with the operator to determine the effect
                                                                                                on circulation of personnel and material flow through the
                                                                                                hangar. Unless the external site constraints dictate otherwise,
                                                                                                the cost of a larger hangar footprint can be offset by improving
                                                                                                the efficiency of the aircraft maintenance cycle to minimise the
                                                                                                loss in revenue.

                                                                                                Stepped or flat roof
                                                                                                The aircraft parked positions depend on the operator’s preferred
tum since the late 1960s, when there was a noticeable trend            Fig 3.                   method of maintenance, which will dictate whether the aircraft
towards longer span hangars to accommodate the increasing              British Airways          is ‘tail-in’ or ‘nose-in’ or whether flexibility for each is required.
fleet size and the introduction of the Boeing 747. In addition, the    casualty hangar, LHR     The choice of roof type should therefore be reviewed on each
inherent flexibility of steel structure enables the building foot-                              project to determine the optimum form.Typical roof profiles are
print to be adjusted relatively easily to accommodate new or                                    illustrated in Fig 5 outlining a typical stepped arrangement and
improved maintenance practices.As a result, the use of concrete                                 a flat roof. Clearly the profiled roof restricts large aircraft to the
has been limited to vertical structure to provide lateral stiffness.                            ‘nose-in’ position, but by reducing the building volume the
   This review therefore concentrates principally on steel frame                                heating or cooling costs will also be reduced substantially.
solutions for long span structures, but discusses the use of                           Fig 6.
concrete for appropriate vertical structural elements that benefit         Multi-bay aircraft
lateral stability.                                                     layout, 100m × 165m

Hangar planning
Client constraints
The clear span and door opening requirements are usually the
primary constraints, but there are others that influence the
strategic design and selection of the structural form, which must
be defined at the outset by the operator. These are as follows:
• type and number of aircraft to be serviced
• single or multi bay arrangements
• minimum wingtip and tail clearances
• suspended or floor mounted access docking equipment
• fire protection installation requirements                                                        Flat roof structures tend to be more popular in warm climates,
• construction height limitations                                                               where heating is not an issue and doors are open continuously.
• flexibility for change or extension                                                           This also allows greater usage of the hangar plan by mixing ‘tail-
• available construction area                                                                   in’ and ‘nose-in’ aircraft. The resultant hangar width is reduced
• time slot for construction                                           Fig 4. (below)           by overlapping the wing zones and accepting that sequencing of
   Since the majority of facilities are constructed on busy            Alternative single       the aircraft movement will be necessary (see Fig 6). A flat roof
airports, available land and construction period will be unique        bay hangar layouts       structure will also allow a drive-through configuration, which is
in each case and the operator requirements must be established                                  beneficial to casualty hangars where minor maintenance is
at the earliest opportunity. This applies particularly to items 7      Fig 5. (bottom)          undertaken and the aircraft are parked for short periods of time.
to 9. The importance and impact of the other requirements are          Alternative hangar       Fig 3 shows the British Airways’ drive through casualty hangar
discussed in the following sections.                                   roof profiles            at Heathrow airport, which is a multi-bay hangar, 100m × 100m
                                                                                                in plan, with 22.5m high folding doors and has been operational
                                                                                                since 1971.
                                                                                                   When considering the form of the roof, it will also be necessary
                                                                                                to establish the impact on the structural solution due to the
                                                                                                drainage requirements. Extensive roof areas will require large
                                                                                                gutters, which are usually best placed at the hangar perimeter.
                                                                                                To achieve the slopes required, the structure can be inclined to
                                                                                                follow the roofline. If the bottom boom remains horizontal then
                                                                                                suspended equipment or crane rails can be connected directly to
                                                                                                the structure. This arrangement is used successfully in many
                                                                                                hangars. The alternative is to adopt parallel booms and incline
                                                                                                the trusses to follow the roof profile. With this arrangement,
                                                                                                suspended equipment must be supported on varying height
                                                                                                brackets.

                                                                                                Suspended equipment
                                                                                                Overhead cranes and other equipment is usually suspended
                                                                                                from the roof structure in the majority of hangars. For long
                                                                                                spans this super-imposed load can be significant and must be
                                                                                                assessed accurately at the commencement of the design.
                                                                                                   The crane lifting capacity will vary for different aircraft types
                                                                                                but it is now common for multi-bridge 15t cranes to be provided

24|The Structural Engineer – 6 August 2002
                                                                                                                         paper: luke/howson


                                                                                            tion. Usually suspended equipment imposes a more stringent
                                                                                            limit on roof deflection than would be normal, in order to prevent
                                                                                            the platform edges impacting on the sides of the aircraft. This
                                                                                            aspect is critical with regard to the fuselage design, where multi
                                                                                            level working platforms usually touch the aircraft skin above
                                                                                            and below the curved sides of the aircraft.

                                                                                            Hangar doors
                                                                                            Door heights vary depending on the aircraft tail height and
                                                                                            presently the highest in service is the Boeing 747-400 series
                                                                                            aircraft at 19.6m. Predictions for the New Larger Aircraft tail
                                                                                            height range up to 25m.
                                                                                               The design and operational aspects of hangar doors can vary
                                                                                            considerably, however, they are almost always floor supported on
                                                                                            fixed rails and only require lateral restraint at door head, this
                                                                                            is usually provided by a roller mechanism. Alternatively, there
                                                                                            are fabric doors, which fold vertically and need to be supported
                                                                                            by an overhead door structure.
                                                                                               Single bay hangars will require an over-run on one or both
                                                                                            sides of the hangar to allow full opening of the doors and unob-
                                                                                            structed aircraft movement (see Fig 8). On large multi-bay
                                                                                            hangars, doors can be contained on multi-rails between gable
with the capability of tandem lifting. The equipment and rail       Fig 7.                  ends (see Fig 9). An alternative to both of these systems is to
loads can usually be represented by a uniformly distributed         British Airways         include a sliding, multi-panel door which can be retracted on a
load of 0.25kPa for the development of the general frame            Maintenance Cardiff,    single rail placed close to the side walls.
concept. These loads are more efficiently carried by sharing        tail and fuselage          The clear door opening height for a B747 is normally not
them over a number of main roof members by including verti-         suspended access        lower than 21.5m and the door thickness will be between
cal bracing to create a partial two way distribution of the load.   docking                 500mm and 700mm, depending on the panel width and wind
   Aircraft docking structures are the main source of loading                               loading characteristics. Door panel widths vary considerably
which is frequently suspended from the hangar roof, in order to     Fig 8. (below)
provide multi level access to the aircraft tail and fuselage. The   Aeroflot Hangar,
loads from these structures are considerable and can vary from      Shannon Airport with
40 to 150t. The tail docking, shown in Fig 7, provides a 6-level    overrun door frame
platform arrangement to access a B747 tail structure and            Fig 9. (right)
weighs 150t including an allowance of 5t for personnel access.      British Airways
These loads will vary depending on the operational sophistica-      Maintenance Cardiff,
tion and size of aircraft to be docked. Such structures must        3 bay hangar with
therefore be identified early in the design process to ensure       nine 25m wide slab
adequate stiffness of the roof structure, since movement between    doors, Cardiff Wales
the aircraft and the access docking is an important considera-      International Airport
                                                                                            from about 9m up to 75m according to the access flexibility
                                                                                            required. For example, the British Airways Maintenance Cardiff
                                                                                            (BAMC), three-bay, heavy maintenance hangar at Cardiff Wales
                                                                                            Airport has nine doors over three aircraft bays (see Fig 9), each
                                                                                            door being approximately 25m wide and placed on three rails,
                                                                                            which allows up to two full bays to be accessed at any time. Other
                                                                                            hangars, however, have included full hangar bay width doors up
                                                                                            to 75m wide. Some doors include personnel access at low level
                                                                                            and an amount of glazing to allow natural lighting in to the
                                                                                            hangar.This is illustrated on the BAMC hangar which limits the
                                                                                            total glazing on the doors to approximately 11%. The preferred
                                                                                            door system must be established at the earliest opportunity in
                                                                                            the design process to identify the impact on the main structure.

                                                                                            Flexibility for hangar adaption
                                                                                            The flexibility to modify or extend a hangar may never be
                                                                                            required, but with aircraft sizes and maintenance procedures
                                                                                            being updated continuously, the hangar layout will almost
                                                                                            inevitably change during the life of the building. Developing a
                                                                                            design concept to allow for change need not place any constraints
                                                                                            on the building design, but if the requirements are identified
                                                                                            early in the process then the requirements can usually be incor-
                                                                                            porated at a lower cost.

                                                                                            Fire systems
                                                                                            Fire protection measures are not normally covered by local build-
                                                                                            ing codes and often a hangar can be identified as a single-storey
                                                                                            building requiring no special measures. However, it is more
                                                                                            usual for the airlines to impose their own standards to minimise
                                                                                            aircraft insurance and this may require active fire suppression
                                                                                            systems to be installed.
                                                                                               Systems for dedicated aircraft positions can be floor mounted,
                                                                                            although it is more common for an overhead deluge to be
                                                                                            included. The resulting pipework imposes significant loads on

                                                                                                            6 August 2002 – The Structural Engineer|25
 paper: luke/howson


                        Table 1: Stepped and flat roof single bay hangars                     bank and distribution runs of main supply pipes through the
  Location               Completed         Span &             Door          Plan Form
                                                                                              roof. Generally the loading is small, around 0.15kPa, but in
                                          depth (m)        height (m)                         concentrated pipe banks loads can reach 5kN/m or higher over
  Aeroflot, Shannon         1987       52m × 57m deep                                         a relatively large bandwidth. Loadings will depend on the valve
  Ireland9                               stepped roof         17.5                            room position relative to the hangar bays and the available
                                                                                              space for pipe work distribution.
  Aeroflot Moscow           1990       67m × 72m deep         23.5                               The NFP A4096 standard also suggests that the vertical struc-
  Russia10                               stepped roof                                         ture is to be protected by passive or water-cooling systems. In
                                                                                              Europe & Asia such applications are usually neutralised by fire
  British Airways           1995        75 × 90m deep      17.5/22.5                          engineering the installations and targeting the aircraft posi-
  Manchester, UK11                       stepped roof                                         tions with deluge and/or foam cannons. Where a workshop is
                                                                                              attached directly to the hangar, separation is necessary and it
  United Airways            1990       79m × 98m deep         23.5                            is usual to provide a firewall to provide 90 minutes protection.
  O’Hare, USA12                         (drive through)
                                                                                              Structural systems
                                                                                              The cost of the steel frame can be as much as 20% of the costs
                                                                                              of the entire project, so it is vital that the structural solution
                                                                                              provides the minimum overall building cost, taking into account
                                                                                              erection and temporary works.
                                                                                                 Hangars are large impressive buildings and they are seldom
                                                                                              similar, although the structural solutions can be categorised
                                                                                              into a number of related families, as outlined below:

                                                                                              •   primary and secondary girder systems
                                                                                              •   space frames
                                                                                              •   cantilevered roof structures
                                                                                              •   arched structures
                                                                                              •   cable stayed

                                                                                                 These categories have been established following an extensive
                                                                                              literature review and are consistent with observations made by
                                                                                              Wallin in a paper prepared for the 1983 Airport Forum8.
                                                                        Fig 10. (above)          In order to achieve economy of material using these proven
                                                                        Aeroflot hangar,      solutions, it would be reasonable to expect some standardisation
                                                                        Moscow                between hangars within each group. However, this seems not to
                                                                                              be the case and it may be due to the fact that the visual impact
                                                                        Fig 11. (left)        and operational approach required by each airline is usually
                                                                        British Airways       different.
                                                                        hangar, Manchester       Primary examples of maintenance hangars, which illustrate
                                                                        (Photo: courtesy of   the application of the structural systems identified, are described
the roof, as well as requiring considerable water storage outside       Booth Doors)          below:
the hangar. The design parameters for the protection systems
are often taken from the US National Fire Protection (NFP)                                    Primary and secondary girder systems – single-bay
A4096 Standard.                                                                               hangars: The hangars summarised in Table 1 are of a similar
  As an example of a typical application, the fire protection                                 form and cover stepped and flat roof structures.
system in the BAMC three-bay hangar at Cardiff Wales airport                                     The main feature of these hangars is that they all have later-
comprised an overhead deluge system placed along the line of                                  ally spanning trusses.
each aircraft fuselage, combined with six foam cannons dedi-                                     The AerRianta hangar at Shannon Airport was designed
cated to each bay. Normal bulbed sprinklers protected areas                                   using ridged trusses and took only 9 months to complete from
below and directly above the mezzanine floor. This was a fire                                 the start of design to end of construction.The AerRianta hangar
engineered installation7 designed to achieve optimum perform-                                 in Moscow, although slightly larger, adopted the same standard
ance whilst minimising cost and space demands for pump rooms                                  form. These two hangars are shown in Figs 8 and 10.
and water storage tanks.                                                                         The British Airways hangar also has a stepped roof but the
  Irrespective of whether an engineered or full overhead deluge                               building footprint has been reduced by incorporating a ‘nose in’
system is installed, there will be a requirement for a vertical pipe                          box, approximately 30m × 20m deep, at the rear and the door
                                                                                              height reduced by incorporating a tail slot (see Fig 11).
                        Table 2: Stepped and flat roof multi bay hangars                         The United Airlines hangar uses a flat roof and incorporates
                                                                                              two sets of hangar doors to allow a drive-through arrangement.
  Location               Completed         Span &             Door          Plan Form
                                          depth (m)        height (m)                            The stability of these single-bay structures is usually provided
  Jan Smuts, South          1982        2 No hangars          244
                                                                                              by diagonal bracing placed in the sidewalls and roof or by
  Africa13                              150m × 100m
                                                                                              moment frames.The average weight of the structural steel used
                                                                                              in these structures has been estimated using the information
  Aer Lingus, Dublin        1991       79m/79m × 96m          210                             contained in the technical papers to be between 70 and 90kg/m2.
  Eire14                              inc central column
                                         stepped roof                                         Primary and secondary girder systems – multi-bay
  Lufthansa H4, M           1992         152m × 80m           22.5                            hangars: The hangars in Table 2 incorporate a large fascia
  Munich 2, Germany15                                                                         girder above the hangar doors for the flat roof structures and a
                                                                                              spine girder at the change in level in the stepped roof hangars.
  BAMC, Cardiff             1993        78.5m /153m           22.5                               The Jan Smuts (see Fig 12) and Lufthansa hangars have a
  Wales16                              × 90m (1/2 bay)                                        similar flat roof arrangement but the latter utilises a deep fascia
                                         stepped roof                                         girder with secondary members which span to the back of the
  JAL, Tokyo                1995        190m × 90m            24.0                            hangar.
  Japan17                                                                                        Both the BAMC and Aer Lingus hangars have a stepped roof,
                                                                                              a form principally adopted to optimise volume and heating costs.

26|The Structural Engineer – 6 August 2002
                                                                                                                          paper: luke/howson


                                                                                              The reduced size of the hangar also helps to minimise the visual
                                                                                              impact. The member sizes are significantly different due to the
                                                                                              difference in spans. The BAMC hangar is shown in Figs 7 and
                                                                                              9 and a facility plan is given in Fig 13.
                                                                                                 The JAL hangar incorporates a flat roof diagrid structure to
                                                                                              utilise the perimeter wall support and a fascia girder above the
                                                                                              hangar doors. The roof structure was constructed at ground
                                                                                              level and jacked into position. An internal view of the hangar is
                                                                                              shown in Fig 14. Larger hangars such as this usually incorpo-
                                                                                              rate various steel grades to deal with the range of member forces
                                                                                              and deflection criteria.
                                                                                                 Typically, this family of hangars usually require 160 to
                                                                                              185kg/m2 of structural steel. However, the JAL hangar is approx-
                                                                                              imately 300kg/m2 due to the fact that the structure has been
                                                                    Fig 12. (above)           designed for high teleplatform loads and seismic conditions.
                                                                    Jan Smuts Hangar 8,
                                                                    twin double bays          Space-frame structures
                                                                                              This form of structure is usually adopted when it is necessary
                                                                    Fig 13. (left)            to accommodate a variable plan shape or when the aspect ratio
                                                                    British Airways           of the hangar allows options for two-way spanning. Examples
                                                                    maintenance Cardiff,      are given in Table 3.
                                                                    building layout,             The British Airways H01 and H02 hangars are rectangular
                                                                    Cardiff Wales             in plan and pioneered the use of a folded plate space structure,
                                                                    International Airport     which was constructed at ground level and jacked into position.
                                                                                              The primary girders are located at the roof step and above the
                                                                                              hangar doors.
                                                                                                 The Eastern Airlines hangar has a flat roof and is designed
                                                                                              using a two-way spanning roof structure where the top chords
                                                                                              span diagonally relative to the face of the hangar and the bottom
                                                                                              chords are arranged orthogonally with the nodes coincident.
                                                                                              This skew chord arrangement covers a 2-bay and 1-bay arrange-
                                                                                              ment with spans of 76m and 61m by 86.5m deep. The central
                                                                                              wall is formed using vertical plane frame trusses to provide
                                                                                              lateral stability.
                                                                                                 The British Airways Casualty hangar, which is a drive-
                                                                                              through concept, has the roof supported by a major tubular
                                                                                              column placed at each corner with fascia girders on all sides.
                                                                    Fig 14. (left)            There are two main diagonal trusses and infill secondary trusses
                                                                    Japan Airlines, Tokyo     in each triangular sector, see Figs 3 and 15. This arrangement
                                                                    (Photo: courtesy of
                                                                    Azusa-Sekki)




                                                                            Fig 15. (right)
                                                                     British Airways New
                                                                     Service hangar, LHR
                                                                       (Photo: courtesy of
                                                                      AMEC Building Ltd)

                                                                          Fig 16. (right)
                                                                    FLS hangar, Stansted
                                                                           facility layout

                        Table 3: Space frame structured hangars
Location              Completed       Span &              Door         Plan Form
                                     depth (m)         height (m)
British Airways H01     1970       138m × 83.5m          23.85
& H02, London           1972        Folded plate
Heathrow18
Eastern Airways         1971       76m/61m/30m            24.4
USA19                              × 86.5m deep

British Airways         1980        100m × 100m           21.0
Casualty Hangar                       Interlocked
London Heathrow20                       trusses
Airforce 1, Andrews     1989        183m × 108m           21.5
Airforce Base,                        Orthogonal
USA21                                   trusses
FLS Stansted            1989         170m × 98m           21.0
UK22                              Cubic orthogonal
                                  vierendeel trusses


                                                                                                             6 August 2002 – The Structural Engineer|27
 paper: luke/howson


                                                                                              structure is efficient if restraint can be provided naturally by
                                                                                              support building structures, otherwise tie-down structure
                                                                                              increases the steel content and tie-down anchors would be
                                                                                              required. Hangars which have taken support from the support
                                                                                              building are American Airlines at Fort Worth, US Navy at
                                                                                              Jacksonville and HAECO in Hong Kong.
                                                                                                 The Brize Norton hangar is based on cantilever trusses
                                                                                              balanced by vertical frames integrated into the new workshop,
                                                                                              the Air France hangar has a central cantilever truss supported
                                                                                              by inclined stays from a tower support and the Otto Lilienthal
                                                                                              hangar incorporates internal columns supporting cantilever roof
                                                                                              trusses at their third point.
was intended to provide maximum flexibility for enlargement             Fig 17.                  The HAECO hangar has stayed supported roof trusses from
and the possibility of changing the direction of drive-through, if      HAECO Hangar,         a series of towers placed along the rear wall of the hangar each
required.                                                               Hong Kong, building   side of a ‘nose/tail’ box which provides a total hangar depth of
   The Airforce 1 hangar is hexagonal in plan and constructed           cross section         90m.The unit weight of steel is approximately 220kg/m2, but this
from orthogonal trusses supported on all sides. Fascia girders are                            allows for significant overhead cranage equipment and
incorporated over the two hangar doors.                                                       suspended docking at the tip zone of the cantilever. The general
   The FLS Aerospace hangar is unique in that the roof is a                                   roof configurations of this hangar are illustrated in Fig 17.
‘cubic’ vierendeel space structure supported continuously on
wide walls and two primary girders directly above the doors.The                               Arched structures
facility layout is illustrated in Fig 16.                                                     The key examples of hangars with external arched structure
   These hangar forms involve a range of structural steel                                     from which the roof plate is suspended and arched shaped roofs
weights, which vary markedly from 185kg/m2 for the FLS                                        structures are shown in Table 5.
hangar through to approximately 270kg/m2 for the British                                         The Lufthansa and Iberia hangars have a major external
Airways Drive Through Hangar, which incorporates consider-                                    arched frame from which the front zone of a uniform depth
able flexibility for modifications.                                                           trussed roof plate structure is suspended.The arched structures
                                                                                              are visible and reach heights of 55m.This allows normal second-
Cantilever structures                                                                         ary structures spanning from the front to the back girders of the
This form of structure appears not to have been used widely but                               hangar to be used.Without the arched form, the fascia girder for
is popular where a multi-bay column-free area is required.                                    this span would be considerably deeper than the general roof
Hangars typical of this form are summarised in Table 4.                                       plate. The Lufthansa hangar structure is shown in Fig 18.
   The cantilever structure allows a totally column-free hangar                                  The KAL hangar roof is supported on three columns and is a
space and can be easily extended laterally. Typical clear spans                               symmetrical arched hyperbolic balanced cantilever truss roof.An
adopted are in the order of 65m and the structural steel weight                               adjacent multi-storey workshop building of the same height
ranges between approximately 135 to 150kg/m2. This form of                                    provides lateral stability.
                                                                                                 The structural steel used for these hangar types varies from
                             Table 4: Cantilever structure hangars                            205 to 235kg/m2.
  Location               Completed        Width &             Door         Plan Form             The smaller arched hangar for Pancorp comprises two arched
                                       cantilever (m)      height (m)                         bays separated by a two-storey workshop. The roof structure is
  Royal Air Force          1967         317.5 × 46.5m         15.0                            assembled flat at ground level and pulled into shape by post-
  Brize Norton                          Tied cantilever                                       tensioning cables that pass through the bottom chord of the roof
  UK23                                                                                        truss.A combination of the arch, smaller span and post-tension-
  Air France               1980         136.8m × 90m,         20.5                            ing reduces the structural steel weight by approximately 25%
  Paris, France24                           56.6m                                             compared with a traditional single-span hangar. However, the
                                       Stayed cantilever                                      construction costs of the post-tensioned structures could not be
  American Airlines        1991          385m × 85m           21.0                            studied to establish a relative comparison.
  Fort Worth                            Tied cantilever
  Houston, Texas25                                                                            Cable stayed structures
  Otto Lilenthal,          1993         160m × 88.5m          18.6                            This arrangement is suitable for long span structures, but the
  Hamburg,                                  58.8m                                             efficiency of the form is dependent on the height of the masts
  Germany26                             Tied cantilever                                       which usually must be contained below the safeguarding enve-
  United States Navy       1996         182m × 41.5m          12.0                            lope of 45m at most airports. Consequently this form of structure
  Jacksonville                         Stayed cantilever                                      is rarely used, an exception being the Lufthansa H1 hangar at
  USA27                                                                                       Munich Airport33 which was completed in 1992 and incorpo-
  Hong Kong Aircraft       1998         220m × 67.7m          22.0                            rates two double bays each with a span of 152m and an overall
  Engineering co Ltd28                 Stayed cantilever                                      depth of 83m (see Fig 19). This hangar also includes four
                                                                                              nose/tail boxes that effectively extend the depth of the hangar
                                                                                              to 112m.The masts rise to 54.5m, well above the normal airport-
                                  Table 5: Arched roof hangars                                safeguarding envelope, and this must have received special
  Location               Completed         Span &             Door         Plan Form          approval. The hangar is an economical structure and benefits
                                          depth (m)        height (m)                         from the concrete masts, relaxed height restrictions, continuity
  Iberia, Madrid           1991          240 × 90m            24.0                            of the roof over the central supports and reduced spans between
  Spain29                                 Split arch                                          suspension points.The form and use of concrete columns reduces
                                                                                              the structural steel weight considerably and the average for the
  Lufthansa                1992         150m × 82m,           22.0                            roof plate is 125kg/m2.
  Mansbergh                               Split arch                                             In summary, the examples used to illustrate each hangar
  Germany30                                                                                   family represent a small but typical sample of existing opera-
  Pancorp                  1993       2 No 97m × 109m       18/22.0                           tional hangars.The roof members have a span/depth ratio in the
  Portland, USA31                       Post tensioned                                        range 12 to 15, which also includes the cable-stayed structure
                                             arch                                             taken between cable support points.The available data indicates
  Korean Air Lines Inc     1997          180m × 90m           23.0                            that the difference in the unit weight of structural steel between
  Kimpo Airport                                                                               different systems for similar spans is small. However, because
  Seoul32                                                                                     of the large footprint such differences are magnified for the total

28|The Structural Engineer – 6 August 2002
                                                                                                                          paper: luke/howson


                                                                      Fig 18.               loading must be considered at the detailed design stage. If areas
                                                                      Arched supported      of the roof are to be boarded out with temporary decking then
                                                                      hangar, Hamburg       the resultant construction loads would need to be co-ordinated
                                                                      (Photo: courtesy of   with the permanent design loads.
                                                                      Assmann, Beraten         Development of the erection strategy, cost of the superstruc-
                                                                      Planen)               ture and programming of the works are vital considerations in
                                                                                            the assessment of the structural solution. If these issues are
                                                                                            appraised early, the design process will benefit from the devel-
                                                                                            opment of a robust cost model.
                                                                                               Another aspect to consider is the procurement of the steel-
                                                                                            work, since and fabrication of the large structural elements is
                                                                                            usually on the critical path. If lead time for fabrication is short,
                                                                                            then for long-span multi-bay hangars it may be prudent to
                                                                                            consider large in situ RC walls or columns for the main supports
                                                                                            to allow an early start on site, and to reduce the overall height
                                                                                            of the structural steel and extent of the fabrication. This
                                                                                            approach was adopted on the Lufthansa H1 cable-stayed
                                                                                            hangar33. The in situ concrete solution also provides good resist-
                                                                                            ance to lateral stability and simplifies bracing requirements.
                                                                                            Concrete box structures can also be used to provide staircase
                                                                                            access through to the roof structure.These measures will reduce
                                                                                            the overall structural steel weight significantly.

                                                                                            Discussion
building. Also, because of the building size, it is not safe to       Fig 19.               There is no single trend for the design of hangar structures since
assume that the minimum weight provides the minimum cost,             Lufthansa 4 Bay       all the individual facilities are so variable. However, there is
since erection and temporary works costs associated with              cable-stayed          noticeably more use of the cantilevered frame solution in recent
hangar construction can be significant.                               structure             hangar design, and this may reflect the need for larger, more flex-
   The relative weight of structural steel for each of the struc-                           ible bay requirements, together with the fact that some facilities
tural families is illustrated in Fig 20. This graph shows a                                 are provided with large support workshops which provide an
progressive increase in the unit area weight with spans ranging                             ideal counter balance. Also, at some airports, reclaimed land
from single bay through to multi-bay hangars using                                          imposes constraints on the design to allow for large settlement.
primary/secondary girders or space-frame systems.The weights                                The cantilever form removes the need for foundations within the
for the special structural systems are also shown for compari-                              hangar area to support the roof and permits the hangar slab,
son. The cantilever structure demonstrates higher unit steel-                               perimeter walls and interface with the apron to settle without
work weights whilst the cable-stayed structural arrangement                                 imposing on the roof structures, except for appropriate head
combined with concrete vertical structure indicates considerable                            sliding joints at the top of the hangar side walls and doors.
reductions in the weight of the steelwork. In general, the rate of                             In the European environment, the structural form has tended
increase in steel weight starts to accelerate for spans over 90m.                           towards the primary and secondary frame arrangements to
Typically, by doubling the span to 180m, the weight of steelwork                            minimise the footprint area and provide a cost-effective solution.
would be increased by over 200%. However, if it is practical to                                Because of the pressure to drive down aircraft maintenance
incorporate a central roof support in wider hangars, then signif-                           costs, new hangar maintenance installations usually need to
icant reduction in the weight of the structural steel is achievable                         demonstrate minimum cost. This often leads to an inelegant
and it would remain similar to a single-bay arrangement.                                    industrial building form, but it does not have to be so since, by
                                                                                            sensitive selection of cladding materials for the building and
Construction                                                          Fig 20.               doors together with intelligent use of glazing, an interesting
Hangar structures involve erection of large structural elements       Comparison of         relief can be created. Furthermore, since hangar structures have
with high temporary works costs and extensive site fabrication.       structural steel      a high engineering content, it is fundamentally important that
Lifting large girders or erecting space frames all have their own     weights               the engineer identifies a range of structural solutions to fit the
unique challenges. Based on the building size                                                                facility plan during the early concept stage, in
and the various frame solutions, the construction                                                            order to provide sufficient flexibility to achieve a
methods would tend towards the options                                                                       creative design whilst retaining a cost-competi-
described below:                                                                                             tive solution. This trend has been supported by
                                                                                                             many of the major airlines which wish to retain
Primary and secondary girder model – lift each                                                               a quality image in keeping with their growing
element individually and, in some cases, tempo-                                                              global status.
rary strutting to columns may be necessary until                                                                The longer term view of hangar development
the building is stabilised.                                                                                  may be that to accommodate the predicted
Space structures – these are usually constructed                                                             increase in the world fleet, aircraft maintenance
at ground level and jacked into position with roof                                                           hubs may need to be established either on new
cladding and services partially installed.                                                                   airports or independent airfields. This approach
Cantilever structures – lift each element individ-                                                           would allow hangar design to be entirely unre-
ually or construct the roof at ground level, includ-                                                         strained by existing airports which have limited
ing the building services and cladding, then jack                                                            space for continued growth.
the structure up to the required position.
   The temporary works solution adopted will be                                                             Concluding remarks
dependent on the balance between site                                                                       The design information provided has been
constraints, costs and the structural solutions. If                                                         extracted from many sources and published tech-
erection is elemental, then temporary access                                                                nical papers and should be used as a guide to be
could involve either mobile access or full tempo-                                                           confirmed and expanded by referring to the refer-
rary boarding throughout. Jack-up systems may                                                               ences provided. The information will, at its very
be preferable for certain structural systems, or                                                            least, provide an aide memoire to assist with the
where height restrictions are present. These                                                                concept design stage and with the development of
aspects and the appropriate serviceability                                                                  creative and cost effective engineering solutions.

                                                                                                            6 August 2002 – The Structural Engineer|29
 paper: luke/howson



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      December-January 1988-1989                                                       22. ‘Watch this space frame’, New Civil Engineer, 26 October 1989, pp30-33
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      No.4, 1983, pp55-66                                                              25. Herrin, John C., PE: ‘American Airlines, column-free space for an airplane
9.    ‘AerRianta international hangar, Shannon Airport’, Arup Journal, 1990                maintenance facility required cantilever long span steel’, Modern Steel
      p.18                                                                                 Construction, May 1992
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      17                                                                                   Construction, November 1996, pp32-36
12.   Ray, R.: ‘United Airlines hangar’, Modern Steel Construction, 1988, pp13-        28. ‘HAECO aircraft base maintenance facility cantilever roof structure’,
      16                                                                                   Construction & Contract News, 6, 1997, pp18-21
13.   ‘Hangar 8, a symphony in structural steel, S.A.’ Construction World , July       29. Martas, Juan Medina, Ingeniero de Caminos, Canales y Puertos,: El Hangar
      1982, pp44-47                                                                        No.6 De Iberia, Altos Vuelos, Cauce, 2000, pp58-65
14.   Walshe, T. A.: ‘Aer Lingus aircraft maintenance facility at Dublin Airport’,     30. Hartmut, Lohl D-ing: ‘Lufthansa hangar’, Besondere Dach, Berotende
      IE Ireland, 3 February 1992                                                          Ingenieure, Edition 1/2, 1995
15.   Moller, P., Adam, V.: ‘Konstruktion bau und montag der flugzeugwert              31. ‘Case History No.2, Hollow structural sections prove efficient and clear-
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17.   ‘Haneda Area Projects Showcase Engineering, Construction Know-How’,                  Beton-und Stahlbetonbau, 1991, H.7




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          The Institution of Structural Engineers
                                                                                         The Institution of Structural Engineers
          REPORT                                                                         The Institution of Civil Engineers


                                                                                         July 2002




          Manual for the design
                                                                                                                                                Manual for the design of reinforced concrete building strutcures (2nd edition)




          of reinforced concrete                                                         Manual for the design
                                                                                         of reinforced concrete
                                                                                         building structures                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        Expiry date

          building structures                                                            SECOND EDITION




          (2nd edition)
          In 1985 the IStructE published its ‘green’ book, the Manual
          for the design of reinforced concrete building structures,                     Published by The Institution of Structural Engineers


          drafted jointly with the ICE. Written by and for practising
          designers, in a concise format, it reflects the logical
          sequence of operations which a designer follows, and
          was compatible with British Standard BS 8110 at that time.
          This revised 2nd edition encapsulates changes arising
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          from amendments to BS 8110, which was republished in
          1997 and further amended in 2001; the publication of
          BS 8002 for the design of earth retaining structures; and
          the publication of BS 8666, which superseded BS 4466. All
          the amendments are signified by a line in the margin.
          The general scope of the Manual remains unchanged in
          that it still covers the majority of reinforced concrete
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          buildings. It continues to offer practical guidance on how
          to design safe, robust and durable structures.
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