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INTRODUCTION
Amongst the natural hazards, earthquakes have the potential for causing the
greatest damages. Since earthquake forces are random in nature & unpredictable,
the engineering tools needs to be sharpened for analyzing structures under the
action of these forces. Performance based design is gaining a new dimension in the
seismic design philosophy wherein the near field ground motion (usually
acceleration) is to be considered. Earthquake loads are to be carefully modeled so
as to assess the real behavior of structure with a clear understanding that damage is
expected but it should be regulated. In this context pushover analysis which is an
iterative procedure shall be looked upon as an alternative for the orthodox analysis
procedures. The promise of performance-based seismic engineering (PBSE) is to
produce structures with predictable seismic performance.
Performance-based engineering is not new. Automobiles, airplanes, and turbines
have been designed and manufactured using this approach for many decades.
Generally in such applications one or more full-scale prototypes of the structure
are built and subjected to extensive testing. The design and manufacturing process
is then revised to incorporate the lessons learned from the experimental
evaluations. Once the cycle of design, prototype manufacturing, testing and
redesign is successfully completed, the product is manufactured in a massive scale.In the automotive industry, for example, millions of automobiles which are
virtually identical in their mechanical characteristics are produced following each
performance-based design exercise.
What makes performance-based seismic engineering (PBSE) different and more
complicated is that in general this massive payoff of performance-based design is
not available. That is, except for large-scale developments of identical buildings,
each building designed by this process is virtually unique and the experience
obtained is not directly transferable to buildings of other types, sizes and
performance objectives. Therefore, up to now PBSE has not been an economically
feasible alternative to conventional prescriptive code design practices. Due to the
recent advances in seismic hazard assessment, PBSE methodologies, experimental
facilities, and computer applications, PBSE has become increasing more attractive
to developers and engineers of buildings in seismic regions. It is safe to say that
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within just a few years PBSE will become the standard method for design and
delivery of earthquake resistant structures. In order to utilize PBSE effectively and
intelligently, one need to be aware of the uncertainties involved in both structural
performance and seismic hazard estimations.
The recent advent of performance based design has brought the nonlinear static
pushover analysis procedure to the forefront. Pushover analysis is a static,
nonlinear procedure in which the magnitude of the structural loading is
incrementally increased in accordance with a certain predefined pattern. With the
increase in the magnitude of the loading, weak links and failure modes of the
structure are identified. The loading is monotonic with the effects of the cyclic
behavior and load reversals being estimated by using a modified monotonic force-
deformation criteria and with damping approximations. Static pushover analysis is
an attempt by the structural engineering profession to evaluate the real strength of
the structure and it promises to be a useful and effective tool for performancebased design.
The seismic performance of the structure can be determined by comparing
demand of the expected earthquake with the capacity of the structure. So, we can
evaluate the performance level of the structure i.e. is it in immediate occupancy
stage or life safety stage or collapse stage etc. So, as per the requirement of the
client one can decide the performance level of the new structure and design it as
per required criteria and also for the existing structures, retrofitting can be done.
Response quantities estimated from the analysis of the building model need to be
compared to acceptable or allowable limits that are termed acceptance criteria.
These limits can be specified both at global level in terms of inter storey drift limits
and at the local level in terms of component demand limits. The limits are function
of performance levels, hence to achieve a higher performance level for a given
hazard level, the acceptable criteria will be higher i.e. like the structure should be
in immediate occupancy stage after expected earthquake.
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NEED OF PERFORMANCE-BASED DESIGN
From the effects of significant earthquakes (since the early 1980s) it is concluded
that the seismic risks in urban areas are increasing and are far from socio-
economically acceptable levels. There is an urgent need to reverse this situation
and it is believed that one of the most effective ways of doing this is through: (1)
the development of more reliable seismic standards and code provisions than those
currently available and (2) their stringent implementation for the complete
engineering of new engineering facilities.
A performance-based design is aimed at controlling the structural damage based on
precise estimations of proper response parameters. This is possible if more
accurate analyses are carried out, including all potential important factors involved
in the structural behavior. With an emphasis on providing stakeholders the
information needed to make rational business or safety-related decisions, practice
has moved toward predictive methods for assessing potential seismic performance
and has led to the development of performance based engineering methods for
seismic design.
ADVANTAGES OF PERFORMANCE BASED SEISMIC
DESIGN
In contrast to prescriptive design approaches, performance-based design provides a
systematic methodology for assessing the performance capability of a building. It
can be used to verify the equivalent performance of alternatives, deliver standard
performance at a reduced cost, or confirm higher performance needed for critical
facilities.
It also establishes a vocabulary that facilitates meaningful discussion between
stakeholders and design professionals on the development and selection of design
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options. It provides a framework for determining what level of safety and what
level of property protection, at what cost, are acceptable to stakeholders based
upon the specific needs of a project.
Performance-based seismic design can be used to:
al buildings with a higher level of confidence that the
performance intended by present building codes will be achieved.
intended by present building codes, but with lower construction costs.
losses) than intended by present building codes.
assess the potential seismic performance of existing structures and estimate
potential losses in the seismic event.
assess the potential performance of current prescriptive code requirements for
new buildings, and serve as the basis for improvements to code-based seismic
design criteria so that future buildings can perform more consistently and reliably.
Performance-based seismic design offers society the potential to be both more
efficient and effective in the investment of financial resources to avoid future
earthquake losses. Further, the technology used to implement performance-based
seismic design is transferable, and can be adapted for use in performance-based
design for other extreme hazards including fire, wind, flood, snow, blast, and
terrorist attack.
The advantages of PBSD over the methodologies used in the current seismic
design code are summarized as the following six key issues:
1. Multi-level seismic hazards are considered with an emphasis on the transparency
of performance objectives.
2. Building performance is guaranteed through limited inelastic deformation in
addition to strength and ductility.
3. Seismic design is oriented by performance objectives interpreted by engineering
parameters as performance criteria.
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4. An analytical method through which the structural behavior, particularly the
nonlinear behavior is rationally obtained.
5. The building will meet the prescribed performance objectives reliably with
accepted confidence.
6. The design will ensure the minimum life-cycle cost.
ATC-40 PROVISIONS for retrofitting of structuresATC stands for Applied Technology Council which is formed in the
United States of America. The main objective of this council is seismic
evaluation and retrofit of concrete buildings. Although the proceduresrecommended in this document are for concrete buildings, they are
applicable to almost all types of buildings. This document provides guidelines
to evaluate and retrofit concrete structures using performance based
objectives. Following steps are recommended by ATC-40 for evaluation and
retrofitting:
1. Determine the primary goal of the project.
2. Select engineering professionals with demonstrated experience in
the analysis, design and retrofit of the buildings in seismically
hazardous region.
3. Decide performance objectives for specific level of seismic hazard.
4. Choose Regular site visits and review of drawings.
5. Check whether applied nonlinear procedure is appropriate or not for
selected structure.
6. Check quality control measures.
7. Perform nonlinear static analysis if appropriate.
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8. Determine inelastic curve known as pushover curve and convert to
capacity spectrum.
9. Obtain response spectrum and convert to ADRS format.
10. Obtain performance point.
11. Prepare construction documents and
12. Monitor construction quality.
Performance objectives
A performance objective has two essential parts a damage state and
level of seismic hazard. Seismic performance is described by designating the
maximum allowable damage state (performance level) for an identified
seismic hazard (earthquake ground motion). A performance objective may
include consideration of damage states for several levels of ground motion
and would then be termed a dual or multiple level performance objectives.
The target performance objective is split into structural performance
level (SP-n, Where n is the designated number) and non-structural
performance level (NP-n, Where n is the designated letter). These may bespecified independently. However, the combination of the two determines
the overall building performance level.
Structural performance levels
Structural performance levels are defined as follows:
1. Immediate Occupancy (SP-1):
It is a state of Limited structural damage, with the basic vertical
and lateral force resisting system. Retaining most of their pre-
earthquake characteristics and capacities.
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2. Damage control (SP-2):
This is a placeholder for a state of damage somewhere between
immediate occupancy and life safety.
3. Life Safety (SP-3):
This is a significant damage state with some margin against total or
partial collapse. Injuries may occur with the risk of life-threatening
injury being low. Repair may not be economically feasible.
4. Limited Stability (SP-4):
This state is a placeholder for a state of damage somewhere
between life safety and structural stability.
5. Structural Stability (SP-5):
This is a Substantial structural damage in which the structural
system is on the verge of experiencing partial or total collapse.
Significant risk of injury exists. Repair may not be technically or
economically feasible.
6. Not considered (SP-6):
This is a placeholder for situations where only non-structural
seismic evaluation or retrofit is performed.
Non-structural Performance levels
Non-structural Performance levels are defined as follows:
1. Operational (NP-A):
Non-structural elements are generally in place and functional.
Backup systems for failure of external utilities. Communications and
transportation have been provided.
2. Immediate Occupancy (NP-B):
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Non-structural elements are generally in place but may not be
functional. No backup system for failure of external utilities is
provided.
3. Life safety (NP-C):
Considerable damage to non-structural components and systems
but no collapse of heavy items. Secondary hazards such as breaks
in high pressure, toxic or fire suppression piping should not be
present.
4. Reduced Hazards (NP-D):
Extensive damage to non-structural components but should notinclude collapse of large and heavy items that can cause significant
injury to groups of people.
5. Not Considered (NP-E):
Non-structural elements, other than those that have an effect on
structural response are not evaluated.
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Table shows Combination of structural and non-structural
performance levels for Building performance levels.
Building Performance Levels
Non-Structural
erformance
levels
Structural performance levels
SP-1
Immediate
Occupancy
SP-2
DamageControl
SP-3
Life
Safety
SP-4
Limited
Safety
SP-5
Structural
Stability
SP-6
Not
Considered
NP-A
Operational
1-A
Operational2-A NR NR NR NR
NP-B
Immediate
Occupancy
1-BImmediate
Occupancy
2-B 3-B NR NR NR
NP-C
Life safety1-C 2-C
3-C
Life safety4-C 5-C 6-C
NP-D
ReducedHazards
NR2-D 3-D 4-D 5-D 6-D
NP-E
Not
considered
NR
NR 3-E 4-E
5-E
StructuralStability
Not
Applicable
Legend
Combination of structural and non-structural performance levels for
Building performance levels
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INELASTIC DYNAMIC RESPONSE OF THE STRUCTUREIn high seismicity areas most of the structures are designed to deform
beyond their elastic limits during the design earthquake. To fully understand
how a structure will perform, inelastic dynamic response of thestructure is to be considered. The two methods to perform inelastic
dynamic response of the structure are nonlinear time history analysis and
pushover analysis.Fig.4.1 describes type of methods to evaluate inelastic
dynamic response of the structure.
Methods to evaluate inelastic dynamic response of the structure
Performance-based methods require reasonable estimates of inelastic
deformation or damage in structures. Elastic Analysis is not capable of
providing this information and Nonlinear dynamic response time history
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analysis is capable of providing the required information, but very time
consuming. Nonlinear static pushover analysis provides reasonable estimates
of inelastic behavior. So, nonlinear static pushover analysis is used to
simplify nonlinear time history analysis process.
STATIC NONLINEAR PUSHOVER ANALYSISIntroduction
Establish an equivalent single-degree-of-freedom system
representative of the dynamic response of the structure in its first mode
which is dominant mode of seismic response for regular structure. It is
achieved by analyzing the structure under a set of slowly increasing
representative lateral loads. The resulting base shear Vs. roof
displacement plot is used to compute its response to any given set of ground
motions. Fig shows General Force Vs. Displacement curve.
General Force Vs. Displacement curve
Pushover analysis is a static nonlinear procedure for evaluation of
seismic performance of structures in which the magnitude of structural load
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is incremented in accordance with some pre-defined pattern. With the
increase in magnitude of loading, weak links and failure modes of the
structure are found. The loading is monotonic with the effect of cyclic
behavior and load reversals being estimated by using a modified monotonic
force-deformation criteria and with damping approximations.
Need for pushover analysis
Elastic analysis gives good indication of the elastic capacity of
structures and indicates where the first yielding will occur. However, it
cannot predict mechanisms and redistribution of forces during progressive
failure and also the potential of progressive collapse. This is possible to a
considerable accuracy with the use of pushover analysis.
The use of inelastic procedure for design and evaluation attempts to
help engineers to have better understanding of how the structure will
behave when subjected to earthquake forces.
Following are the basic need for pushover analysis:
To estimate the peak deformations for a given structure and a
given spectra.
Engineer would be able to see if a given structure would be fully-
operational or near-collapse, or in some other damage-state in
between, after the "expected earthquake".
To indicate which components of the structure is expected to
perform worst and should be retrofitted.
Limitations of pushover analysis
Following are the limitations of pushover analysis
1. Pushover analysis procedure implies that there is separation
between the structural capacity and earthquake demand. There are
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numerous research findings, which establish that structural capacity
and earthquake demand are interrelated.
2. Pushover analysis procedure implicitly assumes that the damage is
a function of the lateral deformation of the structure, neglecting
duration effects, number of stress reversals and cumulative energy
dissipation demand. It is generally accepted that damage of a
structure is a function of deformation and energy.
3. Pushover analysis is a static analysis and neglects inherent dynamic
nature. During an earthquake, the behaviour of a nonlinearly
yielding structure can be described by balancing the dynamic
equilibrium at every time step. By focusing only on the strain
energy of the structure during a monotonic static push, the
procedure can leave a misleading impression that energy associated
with the dynamic components of forces (i.e., kinetic energy and
viscous damping energy) are insignificant. The energy of a
structure under earthquake force is given by,
Ei = Ek + Es +Ev + Ed
Where, Ei earthquake input energy
Ek Kinetic energy
Es Static energy
Ev Viscous damping energy
Ed Controlled damping energy
4. Pushover analysis procedure considers only the lateral earthquake
loading and ignores vertical component of earthquake loading.
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5. Pushover analysis over simplifies the structural modelling. The
procedure assumes that it is possible to substructure a nonlinear
three dimensional structure and characterize its behaviour by two
parameters, base shear force and roof displacement.
6. Pushover analysis procedure does not take into account the
progressive changes in the model properties that take place in a
structure as it experiences cyclic non-linear yielding during an
earthquake.
7. Pushover fails to produce good correlation for earthquakes with
predominantly impulsive ground motions.
ESTIMATION OF DEMAND CURVEEstimates of force and deformation demands in critical regions of
structures have been based on dynamic analysis-first, of simple systems,
and second, on inelastic analysis of more complex structural configurations.
The latter approach has allowed estimation of force and deformation
demands in local regions of specific structural models. Dynamic inelastic
analysis of models of representative structures have been used to generate
information on the variation of demand with major structural as well as
ground-motion parameters. Such an effort involves consideration of the
practical range of values of the principal structural parameters as well as the
expected range of variation of the ground motion parameters. Structural
parameters includes the structure fundamental period, principal member
yield levels, and force displacement characteristics. Input motion of
reasonable duration and varying intensity and frequency characteristics
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normally have to be considered. Useful information on demands has also
been obtained from tests on specimens subjected to simulated earthquake
motions using shaking tables and, the pseudo-dynamic method of testing.
Ground motions during an earthquake produces complex horizontal
displacement patterns which may vary with time. Tracking this motion at
every time step to determine structural design requirements is judged
impractical. For a given structure and a ground motion, the displacement
demands are an estimate of the maximum expected response of the building
during the ground motion. Demand curve is a representation of the
earthquake ground motion. A typical demand curve is shown in Fig. We can
convert the demand curve, which is in terms of spectral acceleration and
time period into the demand spectrum which is a representation of the
capacity curve in ADRS-acceleration displacement response spectra (Sa Vs
Sd) format.
Demand curve
ESTIMATION OF CAPACITY CURVETo survive earthquakes, codes require that structures possess
adequate ductility to allow them to dissipate most of the energy from the
ground motions through inelastic deformations. However, deformations in
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the seismic force resisting system must be controlled to protect elements of
the structure that are not part of the lateral force resisting system. The fact
is that many elements of the structure that are not detailed for ductility will
participate in the lateral force resisting mechanism and can become severely
damaged as a result. This is required in order to provide a ductile system to
resist earthquake forces.
The overall capacity of a structure depends on the strength and
deformation capacities of the individual components of the structure. In
order to determine capacities beyond the elastic limits, some form of
nonlinear analysis is required. This procedure uses sequential elastic
analyses, superimposed to approximate force-displacement diagram of the
overall structure. The mathematical model of the structure is modified to
account for reduced resistance of yielding components. A lateral force
distribution is again applied until additional components yield. The process is
continued until the structure becomes unstable or until a predetermined limit
is reached. A typical capacity curve is shown in Fig. We can convert the
capacity curve, which is in terms of base shear and roof displacement into
the capacity spectrum which is a representation of the capacity curve in
ADRS-acceleration displacement response spectra (Sa Vs Sd) format.
Capacity curve
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PERFORMANCE POINTPerformance point can be obtained by superimposing capacity
spectrum and demand spectrum and the intersection point of these two
curves is a performance point as shown in Fig.
Superimposing demand spectrum and capacity spectrum
Check performance level of the structure and plastic hinge formations
at performance point. A performance check verifies that structural and non-
structural components are not damaged beyond the acceptable limits of the
performance objective for the forces and displacements implied by the
displacement demand.
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PUSHOVER CURVEFor each degree of freedom, one can define a force-displacement
(moment-rotation) curve that gives the yield value and the plastic
deformation following yield. This is done in terms of a curve with values atfive points, A-B-C-D-E, as shown in Fig is called as a pushover curve.
The pushover curve
One can specify additional deformation measures at points IO
(immediate occupancy), LS (life safety), and CP (collapse prevention). These
are informational measures that are reported in the analysis results and
used for performance-based design. They do not have any effect on the
behavior of the structure.
LOADING CRITEIA FOR PUSHOVER ANALYSISThe loading which is to be applied for the pushover analysis is the product of
the storey masses and first mode shape of the building as the first mode is
the most dominant mode in the building usually. The example of the loading
is shown in the fig. below.
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This load was applied to the structure for pushover analysis. This load is
similar to the inverted triangular loading suggested for pushover analysis by
various codes such as ATC-40, etc.
ASSUMPTIONS INCLUDED FOR THE LOADING CRITERIA
1. The material is homogeneous, isotropic and linearly elastic.
2. All columns supports are considered as fixed at the foundation.
3. Tensile strength of concrete is ignored in sections subjected to bending.
4. The super structure is analyzed independently from foundation and soil
medium, on the assumptions that foundations are fixed.
5. The floor acts as diaphragms, which are rigid in the horizontal plane.
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6. Pushover hinges are assigned to all the member ends.
7. The maximum target displacement of the structure is kept at 2.5% of the
height of the building.
Type of hinges:
Yielding and post-yielding behaviour can be modelled using
discrete user-defined hinges. Currently hinges can only be introduced
into frame elements; they can be assigned to a frame element at any
location along that element. Uncoupled moment, torsion, axial force
and shear hinges are available. There is also a coupled P-M2-M3 hinge
which yields based on the interaction of axial force and bending
moments at the hinge location. More than one type of hinge can exist
at the same location, for example, you might assign both a M3
(moment) and a V2 (shear) hinge to the same end of a frame element.
Default hinge properties are provided based on FEMA-356 [19]
criteria.
Default Hinge Properties:
A hinge property may use all default properties, or one may
partially defined and use only some default properties. Default hinge
properties are based upon a simplified set of assumptions that may
not be appropriate for all structures. You may want to use default
properties as a starting point, and explicitly override properties as
needed during the development of your model. Default properties
require that the program have detailed knowledge of the Frame
Section property used by the element that contains the hinge. This
means:
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The material must have a design type of concrete or steel
For concrete Sections:
The shape must be rectangular or circular
The reinforcing steel must be explicitly defined, or else have
already been designed by the program before nonlinear analysis
is performed.
For steel Sections, the shape must be well defined:
General and Nonprismatic Sections cannot be used
Auto select Sections can only be used if they have already been
designed so that a specific section has been chosen before
nonlinear analysis is performed.
For situations where design is required, you can still define and
assign hinges to Frame elements, but you should not run any
nonlinear analyses until after the design has been run.
Default properties are available for hinges in the following degrees
of freedom:
Axial (P)
Major shear (V2)
Major moment (M3)
Coupled P-M2-M3 (PMM)
Methodology to perform Static Nonlinear Pushover
Analysis
General
Two key elements of a performance based design procedure are
demand and capacity. Demand is representation of the earthquake ground
motion. Capacity is a representation of the structures ability to resist the
seismic demand. The performance is dependent on the manner in which
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capacity is able to handle the demand. In other words, the structure must
have the capacity to satisfy demands of the earthquake such that the
performance of the structure is compatible with the objectives of the design.
Nonlinear pushover analysis can be done by capacity spectrum method
and displacement coefficient method.
Capacity spectrum methodCapacity curve
The overall capacity of a structure depends on the strength and
deformation capacities of the individual components of the structure. In
order to determine capacities beyond the elastic limits, some form of
nonlinear analysis is required. This procedure uses sequential elastic
analyses, superimposed to approximate force-displacement diagram of the
overall structure. The mathematical model of the structure is modified to
account for reduced resistance of yielding components. A lateral force
distribution is again applied until additional components yield. The process is
continued until the structure becomes unstable or until a predetermined limit
is reached. A typical capacity curve is as shown in Fig.
Capacity curve
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Capacity spectrum
To convert the capacity curve, which is in terms of base shear and roof
displacement into the capacity spectrum which is a representation of the
capacity curve in ADRS-acceleration displacement response spectra (Sa Vs
Sd) format, the required equations to make the transformation are as
follows (Refer ATC-40, Volume-1, p-8.9):
_________A
_________B
Sa=V/(W*1) _________C
_________D
Where,
PF1 = modal participation factor for the first natural mode.
1 =modal mass coefficient for the first natural mode.
Wi/g = mass assigned to level i.
i1 = amplitude of mode 1 at level i.
N = level N, the level which is the uppermost in the main portion of the
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structure.
V = base shear.
W = building dead weight plus likely live loads.
roof = roof displacement ( V and the associated roof make up points
on the capacity curve ).
Sa = spectral acceleration.
Sd = spectral displacement ( Sa and the associated Sd make up points
on the capacity spectrum ).
First calculate the modal participation factor PF1 and modal mass
coefficient 1 using A and B. Then each point on the capacity curve (V,
roof), calculate the associated point (Sa, Sd) on the capacity spectrum using
C and D.
A typical capacity spectrum is as shown in Fig.
Capacity spectrum
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Demand curve
Ground motions during an earthquake produces complex horizontal
displacement patterns which may vary with time. Tracking this motion at
every time step to determine structural design requirements is judged
impractical. For a given structure and a ground motion, the displacement
demands are an estimate of the maximum expected response of the building
during the ground motion. Demand curve is a representation of the
earthquake ground motion. It is given by spectral acceleration (Sa) Vs. Time
period (T) as shown in Fig.
Demand curve (Traditional spectrum)
Value of Seismic coefficient CA should be taken to be equal to 0.4
times the spectral response acceleration (units of g) at a period of 0.3
seconds i.e. effective peak acceleration (EPA). A factor of about 2.5 times CA
represents the average value of a 5 % damped short period system in the
acceleration domain. The seismic coefficient CV represents 5 % dampedresponse of a 1-second system and when divided by period defines response
in the velocity domain. Fig illustrates the construction of an elastic response
spectrum (Demand curve) (Refer ATC-40, Volume-1, P-4.12).
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Construction of a 5 % damped elastic response spectrum (Demand
curve)
As per proposed draft provisions and commentary on Indian seismic
code IS: 1893 (part-I), equivalent seismic coefficient CA as per IS: 1893
(part-I) is given by,
CA = Z*g*Sa/g(at EPA) _________1
Now,
Cv = 2.5CA*TS _________2
Demand spectrum
To convert Demand curve (traditional spectrum-Sa Vs T format) into
demand spectrum (acceleration displacement response spectrum-Sa Vs Sd
format), following eqn 3 to be used (Refer ATC-40, Volume-1, p-8.10).
Sd = SaT2/42 _________ 3
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A typical demand spectrum is as shown in Fig.
Demand spectrum (ADRS spectrum)
Demand spectra in Traditional and ADRS formats
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Performance point
Performance point can be obtained by superimposing capacity spectrum and
demand spectrum and the intersection point of these two curves is a
performance point. Fig. shows superimposing of demand spectrum and
capacity spectrum.
Superimposing demand spectrum and capacity spectrum
Capacity spectrum superimposed over response spectra in
traditional and ADRS formats
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Check performance level of the structure and plastic hinge formations
at performance point. A performance check verifies that structural and non-
structural components are not damaged beyond the acceptable limits of the
performance objective for the forces and displacements implied by the
displacement demand.
Performance checkAt expected maximum displacement
Once the performance point i.e. spectral acceleration and spectral
displacement is found out, the base shear and roof displacement at the
performance point can be found out from these values. Then, the following
steps should be followed in the performance check:
1. For the global building response, verify
a. Lateral force resistance has not degraded by more than 20 % of
peak resistance.
b. The lateral drifts satisfy the limits given in the Table.
Performance limit
Inter
storey
drift limit
Immediate
Occupancy
Damage
control
Life
Safety
Structural
stability
Maximum
total drift0.01 0.010.02 0.02 0.33 Vi/Pi
Maximum
inelastic
drift
0.005 0.005-0.015 No Limit No Limit
Deformation limits
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2. Identify and classify the different elements in the building. Any of the
following building type may be present:
Beam-column frames, slab-column frames, solid walls, coupled
walls, perforated walls, punched walls, floor diaphragms and
foundations.
3. Identify all primary and secondary components.
4. For each element type, identify critical components and actions to be
checked.
5. The strength and deformation demands at the structures performance
point should be equal to or less than the capacities considering all co-
existing forces acting with the demand spectrum.
6. The performances of secondary elements (such as gravity load
carrying members not part of the lateral load resisting system) are
reviewed for acceptability for the specified performance level.
7. Non-structural elements are checked for the specified performance
level.