Pushover Introduction

8/3/2019 Pushover Introduction

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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.

Documents

Pushover Introduction