midas Gen One Stop Solution for Building and General Structures Pushover Analysis

Transcription

1 midas Gen Pushover Analysis

2 Webinar Schedule Topics Presenter Date February Basic Product & General Use Yaman 2/14, Tue Advanced Concrete Building Design (Beam, Column, Wall, Slab) Ravi 2/28, Tue March Basic Product & General Use Yaman 3/13, Tue Advanced Steel Structure Design Ravi 3/27, Tue April Basic Product & General Use Yaman 4/10, Tue Advanced Pushover Analysis Ravi 4/24, Tue May Basic Product & General Use Yaman 5/15, Tue Advanced Time History Analysis Ravi 5/29, Tue June Basic Product & General Use Yaman 6/12, Tue Advanced Construction Stage Analysis & Column Shortening Ravi 6/26, Tue

3 midas Gen Pushover Analysis Webinar Objective Methods of Analysis for Earthquake Resistant Structures to Pushover Analysis Pushover Analysis of RC Building Pushover Analysis of Steel Building Conclusion

4 Objective 1. 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.

6 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.

7 Methods of Analysis for Earthquake Resistance Structures 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.

8 Methods of Analysis for Earthquake Resistance Structures Analysis Methods Linear Nonlinear Static Dynamic Static Dynamic Equivalent Lateral Load Small Displacement Response Spectrum Analysis Small Displacement Equivalent Lateral Load Small or Large Displacement Nonlinear Response History Analysis Small or Large Displacement Linear Response History Analysis Small Displacement Sequential Yield Analysis Pushover Analysis

10 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.

11 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.

12 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.

13 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.

14 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.

15 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

16 Target Displacement The Target displacement is calculated by d t = C 0 C 1 C 2 C 3 S a T e2 g/4p 2 where: C 0 = Modification factor for SDOF MDOF C 1 = Modification Factor to relate expected maximum inelastic displacements to displacements calculated for liner elastic response C 2 = Modification factor to represent the effect of hysteresis shape on the maximum displacement response C 3 = Modification Factor to represent increased displacements due to dynamic P- effects. S a = Response spectrum acceleration T e = Characteristic period of the response spectrum.

17 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.

19 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

20 = 45,000 Midas Gen Advanced Webinar RC Model G1 LB1 G1 C1 C1 Designation Story Section Number Column Dimension C1 12~15F 8~11F 4~7F 1~3F x x x x 800 Designation Section Number Section Dimension G x 600 LBl x 300 unit : mm

21 Moment/SF Midas Gen Advanced Webinar Hinge Properties Hinge Property C B CP IO LS D E A Rotation/SF B - Yield State IO immediate Occupancy LS Life Safety CP Collapse Prevention C Ultimate State

22 Base Shear (V) Spectral Acceleration (Sa) Midas Gen Advanced Webinar Pushover Curve Roof Displacement (U) Spectral Displacement (Sd) Pushover Curve S S a d V / W / 1 / PF * roof 1 1, roof Capacity Spectrum

23 Spectral Acceleration Spectral Acceleration (Sa) Midas Gen Advanced Webinar Demand Spectrum T 0 T 0 Time Period Acceleration Vs Time Period Spectral Displacement (Sd) Acceleration Vs Displacement S d = S a T 2 /4p 2

24 Spectral Acceleration Midas Gen Advanced Webinar Performance Point Demand Spectrum for effective damping at performance point Capacity Spectrum Spectral Displacement

26 3,000 6,000 G1 G1 G1 3,000 9,000 3,000 Midas Gen Advanced Webinar 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 BR1 10,000 2,500 2,500 2,500 2,500 B C2 G2 C1 BR G2 C2 BR1 BR2 A C2 G2 BR C1 G2 C2 Figure 2. Structural plan Figure 3. Elevation

28 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.

29 midas Gen Q & A