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

Midas Gen – Advanced Webinar

One Stop Solution for Building and General Structures

Objective

1. Introduction to Pushover Analysis. 2. Discussion of Features available in midas Gen for Pushover Analysis. 3. Live demonstration of interpretation of results.

performing

pushover

analysis

and

4. At the conclusion of the webinar attendees will be familiar with pushover analysis and midas Gen applicability to it.


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


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

Nonlinear

Linear

Static

Static

Dynamic

Equivalent Lateral Load Small Displacement

Response Spectrum Analysis Small Displacement

Linear Response History Analysis Small Displacement

Dynamic

Equivalent Lateral Load Small or Large Displacement

Nonlinear Response History Analysis Small or Large Displacement

Sequential Yield Analysis 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


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.


Introduction


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.


Introduction


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.


Introduction


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 building’s occupants created by the damage, and the post earthquake serviceability of the building.


Introduction


Performance Level Operational Level • This is the performance level related to functionality and any required repairs are minor.

Immediate Occupancy level • This corresponds to the most widely used criteria for essential facilities. The building’s spaces and systems are expected to be reasonably usable

Life Safety 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

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


Introduction

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



Introduction


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.


Introduction


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.



Conclusion


Introduction


Pushover Analysis Procedure Process in midas Gen Pushover Global Control

Define Lateral Loads

Define Hinge Properties

Check Pushover Curve and Target Disp.

Perform Analysis

Assign Hinges

Check Hinge Status

Safety Verification

Introduction



RC Model G1

LB1

G1 C1

15@3,000 = 45,000

C1

unit : mm 9000

4000

1200

4000

27200

9000

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


Introduction


Hinge Properties

Hinge Property 1.2

C

B - Yield State

B

IO – immediate Occupancy

1

IO

Moment/SF

0.8

LS

CP

LS – Life Safety

0.6

CP – Collapse Prevention

0.4

C – Ultimate State D

E

0.2

A 0 0

0.005

0.01

0.015

0.02 Rotation/SF

0.025

0.03

0.035

0.04


Introduction


Base Shear (V)

Spectral Acceleration (Sa)

Pushover Curve

Roof Displacement (U)

Spectral Displacement (Sd)

Pushover Curve

Capacity Spectrum

S a  V / W  / 1



S d   roof / PF1 *  1 ,roof




Introduction


Spectral Acceleration (Sa)

Spectral Acceleration

Demand Spectrum

T0

T0

Spectral Displacement (Sd)

Time Period

Acceleration Vs Time Period

Sd = SaT2/4p2

Acceleration Vs Displacement


Introduction


Spectral Acceleration

Performance Point

Demand Spectrum for effective damping at performance point

Capacity Spectrum

Spectral Displacement



Conclusion


Introduction


Steel Model 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

Figure 1. Three-dimensional structural model 2

3

3,000

1

BR1 10,000 2,500

2,500

2,500

2,500 BR

BR1

3,000

G1

C2

BR2 G2

A C2

BR

G2 C1

Figure 2. Structural plan

C2

Figure 3. Elevation

9,000

G2

G1

C1

G1

6,000

C2

3,000

G2

B



Conclusion


Introduction


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

20121030 Gen Pushover Analysis

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