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SEISMORESISTANT
BUILDING ARCHITECTURE
BY:
Ekta Tripathi -801222004
Divya Chopra-801222003
Priyanka kumari-801222012
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INTRODUCTION TO
EARTHQUAKE RESISTANT
STRUCTURES Earthquake-resistant structures are safe
structures designed to withstand earthquake.
While no structure can be entirely immune to damage from
earthquakes, the goal of earthquake-resistant construction isto erect structures that fair better during seismic activity than
their conventional counterparts.
Earthquake-resistant structures are intended to withstand the
largest earthquake of a certain probability that is likely tooccur at their location.
This means the loss of life should be minimized by preventing
collapse of the buildings for rare earthquakes while the loss of
functionality should be limited for more frequent ones.
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SEISMORESISTANT BUILDING
ARCHITECTURE Rational studies along with the knowledge regarding the performance of
building in earthquakes show that the building architecture design would create
maladjustment in building elements that would decrease the seismoresistant
capacity of building and also become the cause of collapse of building.
It is believed that structural analysis in itself is not sufficient to ensure the
seismoresistant stability of the buildings.
There is a need to design an integral seismoresistant system in which all
components of the building can positively interact during the seismic action.
Real compatibility between ARCHITECTURAL andSTRUCTURAL DESIGN avoids a stepping of seismoresistant capacity of that building and also providespositive , efficient and integral SEISMIC RESISTANT
SYSTEM
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Several studies and recommendations have been carried out to
avoid situations affecting negatively the buildings earthquake
resistant behavior.
These studies enable architects to develop a systematic study and a
methodology to be applied to the architectural design of building to
optimize earthquake resistant capacity . This study is called
SEISMO RESISTANT BUILDING ARCHITECTURE.
The SRAS deals with the interaction of each subsystem of the
building during seismic shaking , in order that the architectural
project does not originate structural maladjustment which would
decrease the seismoresistant capacity of the building.
MAIN OBJECTIVES OF SRAS
1. To prevent seismo resistance stepping
2. To optimize the seismo resistance
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MAJOR ASPECTS INVOLVED IN
SEISMORESISTANT BUILDING
CONSTRUCTION
1. SELECTION OF LOAD RESISTING SYSTEM
2. BUILDING CONFIGURATION
3. BASIC DYNAMIC CHARACTERISTICS
4.
QUALITY OF CONSTRUCTION ANDMATERIAL
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LATERAL LOAD RESISTING
SYSTEMS The load resisting system must be of CLOSED LOOPS so that it is
able to transfer all the forces acting vertically or horizontally to the
ground .
BIS has approved 3 major types of lateral load resisting system in
code IS 1893 (Part 1) :2002
MOMENT RESISTING FRAME
BUILDING WITH SHEARWALL OR BEARING WALL
SYSTEM BUILDING WITH DUAL
SYSTEM
LATERALLOAD
RESISTINGSYSTEMS
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1. MOMENT RESISTING FRAMES
Moment-resisting frames can be
constructed of steel, concrete, ormasonry.
Moment frames consist of beamsand columns in which bending ofthese members provides the
resistance to lateral forces.
This system is generallypreferred by architects becausethey are relatively unobtrusivecompared to shear walls or
braced frames , but there may bepoor economic risk unlessspecial damage controlmeasures are taken
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BUILDING WITH SHEAR WALL
OR BEARING WALL SYSTEM Bearing wall systems consist of
vertical load carrying wallslocated along exterior wall linesand at interior locations asnecessary.
Many of these bearing walls arealso used to resist lateral forcesand are then called shear walls
In general , bearing wall systemhas comparable low R valuesince the system lacks
redundancy and has a poorinelastic response capacity.
This system is not muchpreferred by the architects.
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BUILDING CONFIGURATION
Second step in seismo resistant construction is configuration of load
resisting systems of buildings.
IS 1893 ( part 1):2002 has recommended building configuration system in
section 7 for the better performance of building during earthquake.
Most important feature in building configuration is its REGULARITY and
SYMMETRY in horizontal and vertical plane.
Seismic behavior of REGULAR PLANS and IRREGULAR SHAPED
PLANS differ
IRREGULAR SHAPED PLAN is subjected to their asymmetry and can
present local deformation due to presence of reentrant corners or
excessive openings. Both effects give origin to undesired stress
concentrations in some resisting members of buildings..
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REGULAR SHAPED PLAN i.e. ideal rectangular or square
plan , structurally symmetric, with enough in plan stiffness inits diaphragm , presents an ideal behavior because it has
same displacement at every point in the slab.
Therefore building shaped like a box , such as rectangular ,
both in plan and elevation is inherently stronger than the one
that is L-shaped or U-shaped, that is building with wings.
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IRREGULAR SHAPED PLANS
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ARCHITECTURAL
PROBLEMS
STRUCTURAL PROBLEMS REMEDIAL MEASURES
1. Extreme
heights/depthratio
High overturning forces , large
drift causing non structuraldamages , foundation stability
Revise proportion or
special structuralsystem
2. Extreme large
length/depth ratio
Built up large lateral forces in
perimeter , large difference in
resistance of two axes
Experience greater variationsin ground movement and soil
conditions
Sub divide building by
seismic joints
3.Re-entrant
corners
Torsion , stress concentration
at the notches
Separate walls , uniform
box , centre box ,architectural relief ,
diagonal reinforcement
4. Soft story frame Causes abrupt changes of
stiffness at piont of
discontinuity
Add bracings , add
columns braced
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ARCHITECTURAL
PROBLEMS
STRUCTURAL PROBLEMS REMEDIAL MEASURES
5. Variation incolumn stiffness Causes abrupt changes instiffness , much higher
forces in stiffer columns.
Redesign structuralsystem to balance
stiffness
6. Discontinuousshear wall Results in discontinuitiesin load path and stress
conc. For most heavily
loaded elements
Primary concern overthe strength of lower
level column and
connecting beams that
support the load of
discontinuous frame
7. Weak column-
strong beam
Column failure occures
before beam , short column
must try and accommodate
storey height displacement
Add full walls to reduce
column forces , use
light weight curtain
walls with frames
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BUILDING CHARACTERISTICS The seismic force exerted on a building are not externally
developed forces like wind instead they are the response ofcyclic motions at the base of building causing accelerations
and hence inertia force.
The response is therefore dynamic in nature.
The dynamic properties of the structure such asnatural period
,damping and mode shape play a crucial role in determining
the response of buildings.
Other properties such as ductility, building foundation,
response of non-structural elements etc.
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MODE SHAPES AND
FUNDAMENTAL PERIOD The vibration of building consists of fundamental mode of vibration and
additional contribution of various modes which vibrates at higher
frequencies.
In low rise building less than 5 storey high the seismic response dependsprimarily on the fundamental mode of vibration accordingly the period of
vibration of this mode expressed in seconds is one of the most
representative characteristics of the dynamic response of a building.
On the basis of time period building may be classified as- T
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Building with higher natural frequencies and short natural
period tend to suffer higher acceleration but smaller
displacement.
Building with lower natural frequencies and long natural
period tend to suffer lower acceleration but larger
displacement.
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BUILDING FREQUENCY AND
GROUND PERIOD Inertial force generated in the building depend upon the frequencies
of ground on which the building is standing and the building natural
frequency.
When these are near or equal to one another the buildingsresponse reaches a peak level.
This dynamic amplification effect can increase the building
acceleration to a certain value which may double or more than that
of ground acceleration at the base of building.
Past studies shows that predominant period at afirm ground site is
typically in the range .2-.4 sec while the period can reach2 sec or
more on soft ground.
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It is concluded that if the foundation soil is firm, rigid
structure will have more unfavorable seismic response than
the flexible structures, whereas the seismic response of
flexible structure on soft foundation site will less favorable
than the rigid structure.
A spectacular example was in Mexico city during 1985
earthquake, which saw enormous damage in medium height
buildings of 10-20 storey's ,which have period matching the 2
sec period of earthquake motions in the city centre, while
adjacent low rise buildings with much shorter periods wereproportionally far less damaged.
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DAMPING
Damping is the ability of the structural system to dissipate theenergy of the earthquake ground shaking.
Since theearthquake ground shaking is inversely proportional to
damping. The more damping a building possesses ,the sooner itwill stop vibrating which of course highly desirable from the
standpoint of earthquake performances.
Now-a-days some more advanced techniques of earthquake
resistant design and construction employ added damping deviceslike shock absorbers increase damping of the building and so
improve its earthquake performance.
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DUCTILITY
It is defined as the capacity of the building materials, systems orstructures to absorb energy by deforming its elastic range.
The primary task of an engineer designing a building to be
earthquake resistant is to ensure that building will possess
enough ductility.
It is possible to build ductile structures with RC if care is taken
during designing to provide thejoints with sufficient abutments
that can adequately confine the concrete thus permitting it to
deform plastically without breaking.
It is also important for this purpose to ensure that the tension
edges of the structure are adequately reinforced and that there
are sufficient stirrups to ensure that concrete is properly
confined along the compression edge.
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FOUNDATION
Major recommendation on structural design must be taken in
mind.
Foundation should be preferably be designed as continuous
(mat or raft) in order to avoid relative horizontal
displacement.
In case of isolated footing ,they should be joined to each
other by means of foundation beams or ties. These ties
should be designed such that it will bear tension and
compression forces.
If different parts of the building are to be structurally
independentbecause of the shape of their ground plan, their
foundations should also be independent.
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QUALITY OF CONSTRUCTION AND
MATERIALS
The industrially produced materials used in construction such as
cement , reinforcement , brick etc should satisfy minimum
standards of quality and resistance.
a) Quality of concrete-
Grade of concrete specified in design documents may not be
developed during construction mainly due to
Incorrect proportioning.
Insufficient mixing which causes segregation.
Aggregate with excessive impurities or improper grading.
Excessive high w/c ratio.
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b)Construction joint-
A defective concrete joint, which contributed significantly to
causing of failure of many building in past earthquake is due
to
Poor execution of the construction joint/discontinuity.
Not located at the points specified by designer
Accumulation of sawdust, dust and loose materials at the
surface of joint.
c) General detailing requirements-
Proper placing of reinforcement during casting.
Improper confinement and large tie spacing especially in
plastic hinge region.
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Insufficient confinement and anchorage length at joint.
Insufficient concrete cover to reinforcement results resting in
reinforcing bar and crack in surface concrete.
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