Earth Quake Resistance StrucTures by harish1991

VIEWS: 133 PAGES: 14

									                  D.M.S.S.V.H.COLLEGE OF ENGINEERING
                         MACHILIPATNAM – 521 001




                  EARTHQUAKE RESISTANT STRUCTURES

Submitted by :-


K.L.A.V.HARNADH,                           MOHAMMED AZMUDDIN,
B.Tech., III year,                         B.Tech., III year,
Y7CE627,                                   Y7CE615,
Harnadh149@gmail.com                       azu786@gmail.com
Ph. No. 9959063370                         Ph. No. 9700345820.
1.0 INTRODUCTION                              2.0 SEISMIC           EFFECTS         ON
                                              STRUCTURES
An earthquake is the result of a sudden
release of energy in the Earth's crust that   2.1  EARTHQUAKE                GROUND
creates seismic waves. Earthquakes are        MOTION
recorded with a seismometer, also
known as a seismograph. The moment            The seismic waves travel for great
magnitude (or the related and mostly          distances before finally losing most of
obsolete Richter magnitude) of an             their energy. At some time after their
earthquake is conventionally reported,        generation, these seismic waves will
with magnitude 3 or lower earthquakes         reach the earth's surface, and set it in
being     mostly    imperceptible      and    motion, which we surprisingly refer to as
magnitude 7 causing serious damage            earthquake ground motion. When this
over large areas. Intensity of shaking is     earthquake ground motion occurs
measured on the modified Mercalli             beneath a building and when it is strong
scale.                                        enough, it sets the building in motion,
                                              starting with the buildings foundation,
At the Earth's surface, earthquakes           and transfers the motion throughout the
manifest themselves by shaking and            rest of building in a very complex way.
sometimes displacing the ground. When         These motions in turn induce forces
a large earthquake epicenter is located       which can produce damage.
offshore, the seabed sometimes suffers
sufficient displacement to cause a
tsunami. The shaking in earthquakes can       Real earthquake ground motion at a
also trigger landslides and occasionally      particular building site is vastly more
volcanic activity.                            complicated than the simple wave form.
                                              Here it's useful to compare the surface of
In its most generic sense, the word           ground under an earthquake to the
earthquake is used to describe any            surface of a small body of water, like a
seismic event — whether a natural             pond. You can set the surface of a pond
phenomenon or an event caused by              in motion - by throwing stones into it.
humans — that generates seismic waves.        The first few stones create a series of
Earthquakes are caused mostly by              circular waves, which soon being to
rupture of geological faults, but also by     collide with one another. After a while,
volcanic activity, landslides, mine blasts,   the collisions, which we term
and      nuclear      experiments.     An     interference patterns, are being to
earthquake's point of initial rupture is      predominate over the pattern of circular
called its focus or hypocenter. The term      waves. Soon the entire surface of water
epicenter refers to the point at ground       is covered by ripples, and you can no
level directly above the hypocenter.          longer make out the original wave
                                              forms. During an earthquake, the ground
                                              vibrates in a similar manner, as waves of
                                              different frequencies and amplitude
                                              interact with one another.
2.2 BUILDING FREQUENCY AND                    The relationship between frequency F
PERIOD                                       and period T is thus given as

The characteristics of earthquake ground              T=1/F
motions which have the greatest
importance for buildings are the             This means that a short building with a
duration, amplitude (of displacement,        high natural frequency also has a short
velocity and acceleration) and frequency     natural period. Conversely, a very tall
of ground motion.                            building with a low frequency has a long
                                             period.
Frequency: Frequency is defined as the
number of complete cycles of vibration       3.0 PLANNING    TOOL                OF
made by the wave per second                      ARCHITECTURE                   FOR
                                                 EARTHQUAKE
Here we can consider a complete
vibration to be the same as the distance     The behavior of building during
between one crest of the wave and the        earthquakes depends critically on its
next, in other words one full wavelength.    overall shape, size and geometry. Hence,
Surface ground motion at the building        at planning stage itself, architects and
site, then, is actually a complex            structural engineers must work together
superposition of vibration of different      to ensure that the unfavorable features
frequencies. We should also mention          are avoided and a good building
that at any given site some frequencies      configuration is chosen. If both shape
usually predominate                          and structural system work together to
                                             make the structure a marvel.
The response of building to the ground
motion is as complex as the ground           "If we have a poor configuration to start
motion itself, yet typically quite           with, all the engineer can do is to
different. It also begins to vibrate in a    provide a band-aid - improve a basically
complex manner, and because it is now a      poor solution as best as he can.
vibratory system, it also posses a           Conversely, if we start-off with a good
frequency content. However, the              configuration and reasonable framing
buildings vibrations tend to center          system, even a poor engineer cannot
around one particular frequency, which       harm its ultimate performance too
is known as its natural or fundamental       much".
frequency.
                                             3.1 Size of Buildings
The shorter a building is, the higher its
natural frequency. The taller the building    In tall buildings with large weight-to-
is, the lower its natural frequency.         base size ratio the horizontal movement
                                             of the floors during ground shaking is
Period: The natural period is the time it    large. In short but very long buildings,
takes for the building to make one           the damaging effects during earthquake
complete vibration                           shaking are many. And, in buildings
                                             with large plan area, the horizontal
seismic forces can be excessive to be        mid- height of the column of the taller
carried by columns and walls.                one; this can be very dangerous.



3.2 Horizontal Layout of Buildings

Buildings with simple geometry in plan
perform well during strong earthquakes.
Buildings with re-entrant corners, like U,
V, H and + shaped in plan sustain
significant damage. The bad effects of
these interior corners in the plan of
buildings are avoided by making the
buildings in two parts by using a
separation joint at the junction.                          Fig 1

                                             3.5 Building Stiffness and Flexibility

3.3 Vertical Layout of Buidlings             The taller a building, the longer its
                                             natural period tends to be. But the
 Earthquake forces developed at              height of a building is also related to
different floor levels in a building need    another             important        structural
to be brought down along the height to       characteristic: the building flexibility.
the ground by the shortest path, any         Taller buildings tend to be more flexible
deviation or discontinuity in this load      than short buildings. (Only consider a
transfer path results in poor performance    thin metal rod. If it is very short, it is
of building. Buildings with vertical         difficulty to bend it in your hand. If the
setbacks cause a sudden jump in              rod is some what longer, and of the
earthquake forces at the level of            same diameter, it becomes much easier
discontinuity. Buildings that have fewer     to bend. Buildings behave similarly) we
columns or walls in a particular storey or   say that a short building is stiff, while a
with unusually tall storey tend to damage    taller building is flexible. (Obviously,
or collapse which is initiated in that       flexibility and stiffness are really just the
storey.                                      two sides of the same coin. If something
                                             is stiff, it isn't flexible and vice-versa).

                                              Figure shows the Displacement of
3.4 Adjacency of Buildings                   Building according to their Height &
                                             Stiffness
             When two buildings are
close to each other, they may pound on       .
each other during strong shaking. When
building heights do not match the roof of
the shorter building may pound at the
                                              4.0 EFFECT OF EARTHQUAKE
                                             ON REINFORCED CONCRETE
                                             STRUCTURES


                                             A typical RC building is made of
                                             horizontal members (beams and slabs)
                                             and vertical members (columns and
                                             walls), and supported by foundations
                                             that rest on ground. The system
                                             comprising of RC frame. The RC frame
                                             participates in resting the earthquake
                                             forces. Earthquake shaking generates
                                             inertia forces in the building, which are
                                             proportional to the building mass. Since
                                             most of the building mass is present at
                                             floor levels, earthquake induced inertia
                                             forces primarily develop at the floor
                                             levels. These forces travel downwards -
                                             through slabs and beams to columns and
                                             walls, and then to foundations from
                                             where they are dispersed to ground. As
                                             inertia forces accumulate downwards
                                             from the top of the building, the columns
                                             and walls at lower storey experience
            Fig 2                            higher earthquake- induced forces (fig 1)
                                             and are therefore designed to be stronger
Ductility is the ability to undergo          than         those        in        storey
distortion or deformation without            above.
resulting in complete breakage or
failure. To see how ductility can            4.1 Role of Floor Slabs and Masonary
improve a building's performance during
an earthquake,. In response to the ground    Floor slabs are horizontal plate like
motion, the rod bends but does not           elements, which facilitate functional use
break. (of course, metals in general are     of buildings. Usually, beams and slabs at
more ductile than materials such as          one storey level are cast together. In
stone, brick and concrete) The ductility     residential    multi-story     buildings,
of a structure is in fact one of the most    thickness of slabs is only about 110-
important factors affecting its earthquake   150mm. when beams bend in the vertical
performance. One of the primary tasks        direction during earthquakes, these thin
of an engineer designing a building to be    slabs bend along with them .And, when
earthquake resistant is to ensure that the   beams move with columns in the
building will possess enough ductility to    horizontal direction, the slab usually
withstand the size and types of              forces the beams to move together with
earthquakes it is likely to experience       it. After columns and floors in a RC
during its lifetime.                         building are cast and the concrete
hardens, vertical spaces between             5.0 EARTHQUAKE RESISITANCE
columns and floors are usually filled-in     DESIGN
with masonry walls to demarcate a floor
into    functional     spaces    (rooms).    5.1 Conventional Approach
Normally, these masonry walls, also
called infill walls, are not connected to    Design depends         upon providing
surrounding RC columns and beams.            the building with strength, stiffness and
When columns receive horizontal forces       inelastic deformation capacity which are
at floor levels, they try to move in         great enough to withstand a given
horizontal direction, but masonry walls      level of earthquake-generated force.
tend to resist this movement. Due to
their heavy weight and thickness, these      This can be accomplished by selection of
walls attract rather large horizontal        an appropriate structural configuration
forces. However, since masonry is a          and        careful    detailing       of
brittle material, these walls develop        structural members, such as beams and
cracks once their ability to carry           columns, and the connections between
horizontal load is exceeded. Thus            them.
masonry walls is enhanced by mortars of
good strength, making proper masonry         5.2 Basic Approach
courses, and proper packing of gaps
between RC frame and masonry infill          Design depends upon underlying
walls.                                       more advanced        techniques         for
                                             earthquake resistance is not to strengthen
                                             the building, but to reduce the
4.2 Horizontal Earthquake Effects            earthquake generated forces acting upon
                                             it.
 Under gravity loads, tension in the
beams is at the bottom surface of the        This can be accomplished by de-
beam in the central location and is at the   coupling the structure from seismic
top surface at the ends. The level of        ground motion it is possible to reduce
bending moment due to earthquake             the earthquake induced forces in it by
loading depends on severity of shaking       three ways
and can exceed that due to gravity
loading. Thus, under strong earthquake       - Increase natural period of structures by
shaking, the beam ends can develop           BaseIsolation.
tension on either of the top and bottom
faces. Since concrete cannot carry this      - Increase damping of system by Energy
tension, steel bars are required on both     Dissipation Devices.
faces of beams to resist reversals of
bending moment.                              -   By using Active Control Devices.
6.0   EARTHQUAKE               DESIGN       b)     Under moderate but occasional
PHIOSOPHY                                   shaking, the main members may sustain
                                            repairable damage, while the other parts
 Severity of ground shaking at a given      that do not carry load may
location during an earthquake can be        sustain repairable damage.
minor, moderate and strong. Thus
relatively speaking, minor shaking          c)    Under strong but rare shaking, the
occurs frequently; moderate shaking         main members may sustain severe
occasionally and strong shaking rarely.     damage, but the building should not
For instance, on average annually about     collapse.
800 earthquakes of magnitude 5.0-5.9
occur in the world while about 18 for             Earthquake resistant design is
magnitude range 7.0-7.9. So we should       therefore concerned about ensuring that
design and construct a building to resist   the damages in buildings during
that rare earthquake shaking that may       earthquakes are of acceptable variety,
come only once in 500 years or even         and also that they occur at the right
once in 2000 years, even though the life    places and in right amounts. This
of the building may be 50 or 100 years?     approach of earthquake resistant design
                                            is much like the use of electrical fuses in
 Engineers do not attempt to make           houses: to protect the entire electrical
earthquake proof buildings that will not    wiring and appliances in the house, you
get damaged even during the rare but        sacrifice some small parts of electrical
strong earthquake; such buildings will be   circuit, called fuses; these fuses are
too robust and also too expensive.          easily replaced after the electrical over-
Instead the engineering intention is to     current. Likewise to save the building
make buildings earthquake-resistant;        from collapsing you need to allow some
such buildings resist the effects of        pre-determined parts to undergo the
ground shaking, although they may get       acceptable type and level of damage.
damaged severely but would not
collapse during the strong earthquake.           Earthquake resistant buildings,
Thus, safety of people and contents is      particularly their main elements, need to
assured      in      earthquake-resistant   be built with ductility in them. Such
buildings, and thereby a disaster is        buildings have the ability to sway back-
avoided. This is a major objective of       and-forth during an earthquake, and to
seismic design codes throughout the         withstand the earthquake effects with
world.                                      some damage, but without collapse.

6.1 Design Philosophy                       7.0 CONSTRUCTION MATERIALS
                                            FOR EARTH QUAKE RESISTANCE
a) Under minor but frequent shaking,
the main members of the buildings that      In India, most non-urban buildings are
carry vertical and horizontal forces        made in masonry. In the plains, masonry
should not be damaged; however              is generally made of burnt clay bricks
buildings parts that do not carry load      and cement mortar. However in hilly
may sustain repairable damage.              areas, stone masonry with mud mortar is
                                            more prevalent. But now a day we are
very familiar with R.C.C. buildings, and      undergo large elongation before
a variety of new composite constructions      breaking. Concrete is used with steel
materials.                                    reinforcement bars. This composite
                                              material is called as reinforced cement
   1. Masonary                                concrete. The amount and location of
                                              steel in a member should be such that the
Masonry is made up of burnt clay bricks       failure of the member is by steel
and cement or mud mortar. Masonry can         reaching its strength in tension before
carry loads that cause compression (i.e.      concrete reaches its strength in
pressing together) but can hardly take        compression. This type of failure is
load that causes tension (i.e. pulling        ductile failure, and is preferred over a
apart). Masonry is a brittle material,        failure where concrete fails first in
these walls develop cracks once their         compression.
ability to carry horizontal load is
exceeded. Thus infill walls act like          7.1 Earthquake        Design      Resistant
sacrificial fuses in buildings: they          Concept
develop cracks under severe ground
shaking but they share the load of the          If two bars of same length and same
beams and columns until cracking.             cross-sectional area - one made of
                                              ductile material and another of a brittle
   2. Concrete                                material. And a pull is applied on both
                                              bars until they break, then we notice that
      Concrete is another material that       the ductile bar elongates by a large
has been popularly used in building           amount before it breaks, while the brittle
construction particularly over the last       bar breaks suddenly on reaching its
four decades. Cement concrete is made         maximum strength at a relative small
of crushed stone pieces (called               elongation.
aggregate), sand, cement and water
mixed in appropriate proportions.             Amongst the materials used in building
Concrete is much stronger than masonry        construction , steel is ductile, while
under compressive loads, but again its        masonry and concrete are brittle.
behavior in tension is poor. The
properties of concrete critically depend       The correct building components need
on the amount of water used in making         to be made ductile. The failure of
concrete, too much and too little water       columns can affect the stability of
both can cause havoc.                         building, but failure of a beam causes
                                              localized effect. Therefore, it is better to
   3. Steel                                   make beams to be ductile weak links
                                              then columns. This method of designing
     Steel is used in masonry and             RC buildings is called the strong-column
concrete buildings as reinforcement bars      weak-beam design method. Special
of diameter ranging from 6mm to 40mm.         design provisions from IS: 13920-1993
reinforcing steel can carry both tensile      for RC structures ensures that adequate
and compressive loads. Moreover steel is      ductility is provided in the members
a ductile material. This important            where damage is expected.
property of ductility enables steel bars to
7.2 Base Isolation for Earthquake             7.3 Traditional Earthquake Mitigation
                                              Techniques
 It is easiest to see the principle at work
by referring directly to the most widely
used of these advanced techniques,
known as base isolation. A base isolated
structure is supported by a series of
bearing pads, which are placed between
the buildings and building foundation.



 The concept of base isolation is
explained through an example building
resting on frictionless rollers. When the
ground shakes, the rollers freely roll, but
the building above does not move. Thus,
no force is transferred to the building
due to the shaking of the ground; simply,
the building does not experience the                          Fig 3
earthquake. Now, if the same building is
rested on the flexible pads that offer        7.4 Base Isolation Technique
resistance against lateral movements,
then some effect of the ground shaking
will be transferred to the building above.
If the flexible pads are properly chosen,
the forces induced by ground shaking
can be a few times smaller than that
experienced by the building built
directly on ground, namely a fixed base
building. The flexible pads are called
base-isolators, whereas the structures
protected by means of these devices are
called base-isolated buildings. The main
feature of the base isolation technology
is that it introduces flexibility in the
structure.
                                                            Fig 4

                                              Due to the flexibility in the structure, a
                                              robust    medium-rise      masonry      or
                                              reinforced concrete building becomes
                                              extremely flexible. The isolators are
                                              often designed, to absorb energy and
                                              thus add damping to the system. This
                                              helps in further reducing the seismic
response of the building. Many of the          say that the building is deforming. The
base isolators look like large rubber          primary cause of earthquake damage to
pads, although there are other types that      buildings is the deformation which the
are based on sliding of one part of the        building undergoes as a result of the
building relative to other. Also, base         inertial forces upon it.
isolation is not suitable for all buildings.
Mostly low to medium rise buildings            7.6 Spherical Type of Isolation
rested on hard soil underneath; high-rise
buildings or buildings rested on soft soil
are not suitable for base isolation.

               Lead-rubber bearings are
the frequently-used types of base
isolation bearings. A lead rubber bearing
is made from layers of rubber
sandwiched together with layers of steel.
In the middle of the solid lead "plug".
On top and bottom, the bearing is fitted
with steel plates which are used to attach
the bearing to the building and
foundation. The bearing is very stiff and
strong in the vertical direction, but
flexible in the horizontal direction.                           Fig 5

                                               Spherical sliding isolation systems are
7.5 Working Principle
                                               another type of base isolation. The
                                               building is supported by bearing pads
             To get a basic idea of how
                                               that have a curved surface and low
base isolation works, first examine the
                                               friction. During an earthquake the
`(fig 3). This shows an earthquake acting
                                               building is free to slide on the bearings.
on base isolated building and a
                                               Since the bearings have a curved
conventional, fixed-base, building. As a
                                               surface, the building slides both
result of an earthquake, the ground
                                               horizontally and vertically. The forces
beneath each building begins to move. In
                                               needed to move the building upwards
(fig 3) it is shown moving to left. Each
                                               limits the horizontal or lateral forces
building responds with movement which
                                               which would otherwise cause building
tends towards the right. The buildings
                                               deformations. Also by adjusting the
displacement in the direction opposite
                                               radius of the bearings curved surface,
the ground motion is actually due to
                                               this property can be used to design
inertia. The inertia forces acting on a
                                               bearings that also lengthen the buildings
building are the most important of all
                                               period of vibration.
those generated during an earthquake.

            In addition to displacing          8.0   ENERGY              DESSIPATING
towards right, the un-isolated building is     DEVICES FOR              EARTHQUAKE
also shown to be changing its shape            RESISTANCE
from a rectangle to a parallelogram. We
Another approach for controlling seismic      Friction Dampers (energy is absorbed
damage in buildings and improving their       by surfaces with friction between them
seismic performance is by installing          rubbing against each other)
Seismic Dampers in place of structural
elements, such as diagonal braces. These      Yielding Dampers (energy is absorbed
dampers act like the hydraulic shock          by metallic components that yield)
absorbers in cars - much of the sudden
jerks are absorbed in the hydraulic fluids    Viscoelastic dampers (energy is
and only little is transmitted above to the   absorbed by utilizing the controlled
chassis of the car. When seismic energy       shearing of solids)
is transmitted through them, dampers
absorb part of it, and thus damp the              Thus by equipping a building with
motion of the building.                       additional devices which have high
                                              damping capacity, we can greatly
                                              decrease the seismic energy entering the
                                              building.

                                              8.1 Working Principle




                                                                 Fig 7

                                               The construction of a fluid damper is
                                              shown in (fig). It consists of a stainless
                                              steel piston with bronze orifice head. It
                                              is filled with silicone oil. The piston
                                              head utilizes specially shaped passages
                                              which alter the flow of the damper fluid
                                              and     thus    alter   the     resistance
                 Fig 6                        characteristics of the damper. Fluid
                                              dampers may be designed to behave as a
Commonly used        types    of   seismic    pure energy dissipater or a spring or as a
dampers include:                              combination of the two.

Viscous Dampers (energy is absorbed                       A fluid viscous damper
by silicone-based fluid passing between       resembles the common shock absorber
piston cylinder arrangement)                  such as those found in automobiles. The
                                              piston transmits energy entering the
system to the fluid in the damper,                           The     latest   Friction-
causing it to move within the damper.        ViscoElastic Damper Device (F-VEDD)
The movement of the fluid within the         combines the advantages of pure
damper fluid absorbs this kinetic energy     frictional and viscoelastic mechanisms
by converting it into heat. In               of energy dissipation. This new product
automobiles, this means that a shock         consists of friction pads and viscoelastic
received at the wheel is damped before it    polymer pads separated by steel plates as
reaches the passengers compartment. In       shown below. A prestressed bolt in
buildings this can mean that the building    combination with disk springs and
columns protected by dampers will            hardened washers is used for
undergo considerably less horizontal         maintaining the required clamping force
movement and damage during an                on the interfaces as in original FDD
earthquake.                                  concept.

8.2 Second Type of Energy Dissipation        8.3 Active Control          Devices     for
Devices                                      Earthquake Resistance

         The innovative methods for          After development of passive devices
control of seismic vibrations such as        such as base isolation and TMD. The
frictional and other types of damping        next logical steps is to control the action
devices are important integral part of       of these devices in an optimal manner by
seismic isolation systems as they severe     an external energy source the resulting
as a barrier against the penetration of      system is known as active control device
seismic energy into the structure. In this   system. Active control has been very
concept, the dampers suppress the            widely used in aerospace structures. In
response of the isolated building relative   recent years significant progress has
to its base.                                 been made on the analytical side of
                                             active control for civil engineering
        The novel friction damper device     structures. Also a few models explains
consists of three steel plates rotating      as shown that there is great promise in
against each other in opposite directions.   the technology and that one may expect
The steel plates are separated by two        to see in the foreseeable future several
shims of friction pad material producing     dynamic        "Dynamic          Intelligent
friction with steel plates.                  Buildings" the term itself seems to have
                                             been joined by the Kajima Corporation
        When an external force excites a     in Japan. In one of their pamphlet the
frame structure the girder starts to         concept of Active control had been
displace horizontally due to this force.     explained in every simple manner and it
The damper will follow the motion and        is worth quoting here.
the central plate because of the tensile
forces in the bracing elements. When the                 People standing in swaying
applied forces are reversed, the plates      train or bus try to maintain balance by
will rotate in opposite way. The damper      unintentionally bracing their legs or by
dissipates energy by means of friction       relaying on the mussels of their spine
between the sliding surfaces.                and stomach. By providing a similar
                                             function to a building it can dampen
immensely     the   vibrations  when        2) Tendon Control
confronted with an earthquake. This is
the concept of Dynamic Intelligent          Various analytical studies have been
Building (DIB).                             done using tendons for active control.
                                            At low excitations, even with the active
            The philosophy of the past      control system off, the tendon will act in
conventional a seismic structure is to      passive modes by resisting deformations
respond passively to an earthquake. In      in the structures though resulting tension
contrast in the DIB which we propose        in the tendon. At higher excitations one
the building itself functions actively      may switch over to Active mode where
against earthquakes and attempts to         an actuator applies the required tension
control the vibrations. The sensor          in tendons.
distributed inside and outside of the
building transmits information to the       3) Other Methods
computer installed in the building which
can make analyses and judgment, and as      The liquid sloshing during earthquakes
if the buildings possess intelligence       has assumed significance importance in
pertaining to the earthquake amends its     view of over flow of petroleum products
own structural characteristics minutes by   from storage tank in post earthquakes.
minute.                                     One of the important consideration with
                                            sloshing is that is associated with a very
8.4 Control Force Devices                   low damping. The wave height was
                                            controlled through force applied to the
      Many ways have been proposed to       side wall by a hydraulic actuator. The
apply control forces to a structure. Some   active control successfully reduced wave
of these have been tested in laboratory     heights to the level of 6% of those
on scaled down models. Some of the          without control, for harmonic excitations
ideas have been put forward for             at sloshing frequency. For earthquake
applications of active forces are briefly   type excitation the wave heights were
described in the following:                 reduced to 19% level.

1)   Active     tuned   Mass   Dampers      9.0Tips to Design
(TMD)
                                            Is it possible to construct Earthquake-
these are in passive mode have been         proof buildings? Maybe it is, but the
used in a umber of structures as            costs can be huge. So, only Nuclear
mentioned earlier. Hence active TMD is      Power Plants can afford to be
a natural extension. In this system 1%      Earthquake Proof. For the rest of us, its
of the total building mass is directly      earthquake resistant buildings, so that we
excited by an actuator with no spring       can minimize the loss of life and
and dash pot. The system has been           property,
termed as Active Mass Driver (AMD).
The experiments indicated that the          Earthquakes do not kill people, but
building vibrations are reduced about       actually people are killed by the collapse
25% by the use of AMD.                      of badly designed and constructed
                                            buildings. But, with the different types
of new materials available in our                  capacity, then it should be
inventory, it is feasible to construct an          divided into two three smaller
earthquake-resistant building.                     tanks and should be kept at
                                                   different locations to maintain
Some care should be taken while                    balance of cottage-building.
constructing a building in earthquake             If the column length is more than
prone areas. Special attention should be           12 feet. Then bracing beams
given to Structural Design of the                  should be provided in between
structure. Here are some tips for                  the column at regular intervals.
designing safer structures.                        Bracing beams strengthen a
                                                   column, and allow construction
      Building should be of regular               of multistoried buildings.
       shapes. Cylindrical structures             The      columns      should    be
       perform better in high-wing areas           connected at each level.
      Architect should try to design the         For strengthening the brick work,
       building as aerodynamic as                  a sill or a lintel should be
       possible. This reduces the effect           provided at every 3 feet level and
       of wind load on tall structures             R.C.C. wall should be taken
      There should no odd shapes in               where it is possible.
       elevation and the whole building           Cottage-building should not
       should be in balance. The centre            contain very large and heavy
       of gravity of buildings should not          windows. They are bound to
       move                                        weaken the structure.
      Cantilever projections should be           The glass used in any structure
       minimum and their length should             should fiber reinforced glass or
       not be more than 3 to 4 feet.               wire glass
      The span between the columns
       should be as small as possible.      12.0 CONCLUSION
      Point loads on load-carrying
       beams should be avoided.             Conventional approach to earthquake
      The dead loads on the cottage        resistant design of buildings depends
       building should not be increased     upon providing the building with
       unnecessarily.                       strength,    stiffness and    inelastic
      The sunk portions of WC and          deformation capacity. But the new
       bath should be minimum.              techniques like Energy Dissipation and
      Building should be a Reinforced      Active Control Devices are a lot more
       Concrete framed structure. It        efficient and better.
       provides better stability and
       reliability in Earthquake-prone       If we manage to construct our buildings
       areas.                               this way, we will be capable to fight the
      Cottage-building’s      foundation   Earthquake and preventing the trail of
       should be placed on hard and         loss of life and property that an
       level ground.                        Earthquake leaves behind.
      There should not be very large
       overhead water tanks than are
       required. If it has to have larger

								
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