SEISMIC EVALUATION OF RC FRAME BUILDINGS USING PUSHOVER AND NON-LINEAR DYNAMIC ANALYSIS

Abstract

Earthquake is one of the most disastrous forms of natural calamities which occurs in almost all regions of the world. It is difficult to predict their occurrence. The accurate prediction may, perhaps save lot of lives, but may not save immovable property like buildings and other structures. Therefore for earthquake hazard mitigation it is necessary to evaluate the seismic capacity of existing structures and to take the remedial measures for its retrofitting. There are a large number of structures that have primary structural system which don't meet current seismic requirements due to many reasons like low ductility of building designed and detailed by earlier versions of code, deterioration of strength of concrete, fire damage, foundation settlement etc which leads to deterioration of earthquake resistance of structure while omission in design and building construction is also a factor which results in low ductility of buildings. In the present study three two bays RC frames are considered viz. 4 storey RC frame, 8 storey RC frame and 12 storey RC frame. All the three frames are designed using STAAD PRO software first for (a) gravity loading as per IS: 456(2000) and then for (b) seismic loading with ductile detailing as per IS: 13920(1993). Seismic evaluation of the designed frames is then carried out with nonlinear static (pushover) analysis and nonlinear dynamic (time history) analysis using SAP2000 software. Nonlinear material modeling and ductility evaluation of frame sections are done using XTRACT software. For nonlinear dynamic analysis time history data of Chichi earthquake (09/20/99) TAIWAN with PGA=1.157g, Northridge earthquake, Cape Mendocino earthquake, Elcentro earthquake and Lomapreita are used. Results of nonlinear dynamic analysis and nonlinear static (pushover) analysis are compared by making the maximum displacement obtained by nonlinear dynamic analysis equal to displacement at performance point of nonlinear static (pushover) analysis using spectral compatible time history programme (Mathur). Result comparison includes the comparison of base shear, displacement and hinge formation for the considered RC frames designed with (a) gravity load and (b) seismic load using static pushover analysis and nonlinear dynamic analysis. Failure pattern comparison includes the comparison of hinge formation at performance point (pushover analysis) and hinge formation using nonlinear dynamic analysis..