20121030 Gen Pushover Analysis

midas Gen One Stop Solution for Building and General Structures

Pushover Analysis


Pushover Analysis

Webinar Objective

Methods of Analysis for Earthquake Resistant Structures

Introduction to Pushover Analysis

Pushover Analysis of RC Building

Pushover Analysis of Steel Building

Conclusion

One Stop Solution for Building and General Structures Midas Gen Advanced Webinar

1. Introduction to Pushover Analysis.

2. Discussion of Features available in midas Gen for Pushover

Analysis.

3. Live demonstration of performing pushover analysis and

interpretation of results.

4. At the conclusion of the webinar attendees will be familiar with

pushover analysis and midas Gen applicability to it.

Objective


Pushover Analysis

Webinar Objective





Conclusion

One Stop Solution for Building and General Structures Midas Gen Advanced Webinar Methods of Analysis for Earthquake Resistance Structures

Design Methods

Force Based Design

Elastic Response Acceleration is determined form the estimated structural period and given design

elastic response spectrum.

Modified design acceleration is obtained by dividing the Elastic Response Acceleration by Response

Reduction Factor (R)

Design Force is calculated using modified design acceleration.

Displacement Check is made after the structural members satisfy the Force requirements.

Problems :-

The distribution of design forces are based on initial estimate of stiffness and as stiffness is dependent

on the strength of elements, this cannot be know until the design process is complete.

Distribution of seismic forces between elements based on initial stiffness is illogical, as it incorrectly

assumes different elements can be forced to yield simultaneously.

Ductility capacity is a function of structural geometry, not just of structural type. Hence it is inappropriate

to specify a same displacement ductility factor for all structures of the same type.


Design Methods

Performance Based Design/ Displacement Based Design

Importance of deformation rather than strength in seismic performance is gaining more popularity in

recent times due to the deficiencies inherent in the force-based system of seismic design.

The design is carried out by specifying a target displacement.

There is no need to use a force reduction factor

The inelastic nature of the structure during a earthquake is directly addressed.

Displacement based design procedure can provide a reliable indication of damage potential.


Analysis Methods

Linear

Static

Equivalent Lateral Load

Small Displacement

Dynamic

Response Spectrum Analysis

Small Displacement

Linear Response History Analysis

Small Displacement

Nonlinear

Static

Equivalent Lateral Load

Small or Large Displacement

Dynamic

Nonlinear Response History Analysis

Small or Large Displacement

Sequential Yield Analysis

Pushover Analysis


Pushover Analysis

Webinar Objective





Conclusion

One Stop Solution for Building and General Structures Midas Gen Advanced Webinar Introduction

Why Pushover Analysis

Pushover Analysis in the recent years is becoming a popular method of predicting seismic

forces and deformation demands for the purpose of performance evaluation of existing and

new structures.

Pushover analysis is a partial and relatively simple intermediate solution to the complex

problem of predicting force and deformation demands imposed on structures and their

elements by severe ground motion.

Pushover analysis is one of the analysis methods recommended by Eurocode and FEMA

273.


Why Pushover Analysis

Pushover analysis provides valuable insights on many response characteristics like

Force Demand on Potentially brittle elements.

Consequences of strength deterioration of individual elements on structural behavior.

Identification of critical regions in which the deformation demands are expected to be

high and that have to become the focus of through detailing.

Identification of strength discontinuities in plan or elevation that will lead to changes in

dynamic characteristics in the inelastic region.

Verification of completeness and adequacy of load path, considering all structural and

non structural elements of the structural system.


What is Pushover Analysis

- Is a technique by which a structure is subjected to a incremental lateral load of certain

shape.

- The sequence of cracks, yielding, plastic hinge formation and failure of various

structural components are noted.

- The structural deficiencies are observed and rectified.

- The iterative analysis and design goes on until the design satisfies a pre-established

criteria.

- The performance criteria is generally defined as Target displacement of the structure

at roof level.


Performance Level

- Performance Level is defined as the expected behavior of the building in the design

earthquake in terms of limiting levels of damage to the structural and nonstructural

components

- The limiting condition is described by the physical damage within the building, the

threat to life safety of the buildings occupants created by the damage, and the post

earthquake serviceability of the building.


Performance Level

This is the performance level related to functionality and any required repairs are minor.

Operational Level

This corresponds to the most widely used criteria for essential facilities. The buildings spaces and systems are expected to be reasonably usable

Immediate Occupancy level

This level is intended to achieve a damage state that presents an extremely low probability of threat to life safety, either from structural damage or from falling or tipping of nonstructural building component

Life Safety Level

This damage state addresses only the main building frame or vertical load carrying system and requires only stability under vertical loads.

Collapse Prevention Level


Seismic hazard

Seismic Hazard is a function of

- The Building Performance level

- The Mapped Acceleration Parameters

- The Site Class Coefficients

- The Effective structural damping

- The fundamental Structural Period

The general response spectrum is formulated


Target Displacement

The Target displacement is calculated by

dt = C0C1C2C3SaTe2g/4p2

where:

C0 = Modification factor for SDOF MDOF

C1 = Modification Factor to relate expected maximum inelastic displacements to

displacements calculated for liner elastic response

C2 = Modification factor to represent the effect of hysteresis shape on the

maximum displacement response

C3 = Modification Factor to represent increased displacements due to dynamic P-

effects.

Sa = Response spectrum acceleration

Te = Characteristic period of the response spectrum.


Reasons for Performing Pushover Analysis

Why Pushover Analysis over Nonlinear Dynamic Analysis

To run a full dynamic, non linear analysis on even a simple structure takes a long

time. But with pushover analysis accurate results can be obtained in fractions of the

time it would take to get any useful results from the fully dynamic analysis.

When performing a dynamic analysis, it is best to use a series of earthquakes. The

Pushover Analysis naturally accounts for all earthquakes with the same probability of

exceedance by predicting the maximum displacement that can be expected in the

form of the Target Displacement.


Pushover Analysis

Webinar Objective





Conclusion


Pushover Analysis Procedure

Pushover Global Control

Define Lateral Loads

Define Hinge Properties

Assign Hinges Perform Analysis

Check Pushover Curve and

Target Disp.

Check Hinge Status

Safety Verification

Process in midas Gen


RC Model

15

@3

,00

0 =

45

,00

0

9000 9000

27200

4000 40001200

unit : mm

C1 C1

G1 LB1 G1

Designation Story Section Number Column Dimension

C1

12~15F

8~11F

4~7F

1~3F

104

103

102

101

500 x 500

600 x 600

700 x 700

800 x 800

Designation Section Number Section Dimension

G1 21 350 x 600

LBl 31 200 x 300


Hinge Properties

0

0.2

0.4

0.6

0.8

1

1.2

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04

Mo

men

t/S

F

Rotation/SF

Hinge Property

A

B C

D E

IO LS

CP

B - Yield State

IO immediate Occupancy

LS Life Safety

CP Collapse Prevention

C Ultimate State


Pushover Curve

Roof Displacement (U)

Base S

hear

(V)

Pushover Curve

Spectral Displacement (Sd)

Spectr

al A

ccele

ration

(Sa)

Capacity Spectrum

roofroofd

a

PFS

WVS

,1

1

1*/

//


Demand Spectrum

Spectr

al A

ccele

ration

Time Period

T0

Sd = SaT2/4p2

Acceleration Vs Time Period

Spectr

al A

ccele

ration (

Sa)

Spectral Displacement (Sd)

T0

Acceleration Vs Displacement


Performance Point

S

pe

ctr

al A

cce

lera

tio

n

Spectral Displacement

Demand Spectrum for effective

damping at performance point

Capacity Spectrum


Pushover Analysis

Webinar Objective





Conclusion


Steel Model

Figure 3. Elevation

Figure 1. Three-dimensional structural model

6,0

00

10,000

2,500 2,500 2,500 2,500

A

B

1 2 3

G2

G2

G2G2

C2 C2

C2C2 C1

C1

G1

G1

G1

BR

BR

3,000

3,000

3,000

9,000

BR1

BR1

BR2

Figure 2. Structural plan

Section Name Section ID Section DB Section Size

C1 1 UNI HEA240

C2 2 UNI HEA300

G1 21 UNI HEA280

G2 22 UNI IPE240

Brace1 31 UNI HEA160

Brace2 32 UNI HEA120


Pushover Analysis

Webinar Objective





Conclusion


Conclusion

- Pushover Analysis is a very useful tool for the evaluation of New and existing structures.

- Pushover Analysis provided much useful information that cannot be obtained from elastic

static and dynamic analysis.

- Pushover Analysis provides a relatively simple solution than nonlinear Dynamic analysis

and more realistic and comprehensive solution than linear elastic analysis.

- Push over analysis require considerable amount of understanding of the subject by the

engineer.

- Pushover analysis is approximate in nature and is based on static loading and it cannot

represent the dynamic phenomena with a large degree of accuracy.

- Pushover Analysis does not create good solutions, it only evaluates solution.

- Load pattern choice makes a huge difference to the analysis results.


Q & A

Documents

20121030 Gen Pushover Analysis