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Non-Linear Static Analysis for Buildings

 

Seismic analysis of buildings can be categorized depending upon the sophistication of modeling adopted for the analysis. Buildings loaded beyond the elastic range can be analyzed using Non-Linear static analysis, but in this method one would not be able to capture the dynamic response, especially the higher mode effects. This is pushover analysis. There is no specific code for NLSA. This procedure leads to the capacity curve which can be compared with design spectrum/DCR of members and one can determine whether the building is safe or needs strengthening and its extent.

The capacity of structure is represented by pushover curve. The most convenient way to plot he load deformation curve is by tracking the bas shear and the roof displacement. The pushover procedure can be presented in various forms can be used in a variety of forms for the use in a variety of methodologies. As the name implies it is a process of pushing horizontally, with a prescribed loading pattern, incrementally, until the structure reaches the limit state. There are several types of sophistication that can be used over for pushover curve analysis.

 

Level-1:           It is generally used for single storey building, whereat a single concentrated horizontal force equal to base shear applied at the top of the structure and displacement is obtained.

Level-2:           In this level, lateral force in proportion to storey mass is applied at different floor levels in accordance with IS:1893-2002 (Part-I) procedure, and story drift is obtained.

Level-3:           In this method lateral force is applied in proportion to the product of storey masses and first mode shape elastic model of the structure. The pushover curve is constructed to represent the first mode response of structure based on the assumption that the fundamental mode of vibration is the predominant response of the structure. This procedure is valid for tall buildings with fundamental period of vibration upto 1 sec.

Level-4:           This procedure is applied to soft storey buildings, wherein lateral force in proportion to product of storey masses and first mode of shape of elastic model of the structure, until first yielding, the forces are adjusted with the changing the deflected shape.

Level-5:           This procedure is similar to level 3 and level 4 but the effect of higher mode of vibration in determining yielding in individual structural element are included while plotting the pushover curve for the building in terms of the first mode lateral forces and displacements. The higher mode effects can be determined by doing higher mode pushover analysis. For the higher modes, structure is pushed and pulled concurrently to maintain the mode shape.

 

 

Case Study of Non-Linear Static Analysis using SAP2000

 

 



Introduction to Non-Linear Static Push-over Analysis

What is Non-Linear Static Push-over Analysis?

Purpose of Push-over Analysis

Target Displacement

Non-Linear Static Analysis for Buildings

Case Study of Non-Linear Static Analysis using SAP2000

Limitations of Non-Linear Static Push-over Analysis

Conclusion & References