DIRECTIONAL EFFECTS IN SEISMIC RESPONSE OF BUILDINGS

Abstract

Earthquake is an extreme event for building and infra structure which has to be dealt with innovative and simple structural solutions. The search for a simpler solution which gives an insight into the nonlinear behavior of the structure and can be adopted in the codes has lead to the development of Pushover Analysis Procedure. In reality earthquake motion is three dimensional and the direction of the major component of motion with reference to the building orientation cannot be known in advance. Present day practice aims at ., _ designing the building by considering its response along principal axes. However In real life the but,dings have some amount of torsional coupling and the components particularly the columns have interaction between the responses due to loading in the two directions. An attempt has been made in this thesis to study the behavior of building in different directions by developing response envelopes for a ten storied building. Pushover analysis has been used as a tool for the study of the behavior of the structure in different directions and to develop response envelopes for different parameters. Nonlinear Time history analyses using unidirectional and bi-directional time history records have been used to evaluate the results obtained from the pushover procedure. Comparison, of response envelopes developed from different variations of pushover loads has also been made to study the accuracy of the results predicted. It has been observed that the triangular variation of Pushover load along the height of the buildings results in estimation of response closer to that obtained from Nonlinear Time History Analysis (NLTHA), compared to the parabolic distribution of pushover loads. Further the response envelopes obtained by pushover analysis are fair bounds to the response of the building to bidirectional ground motion. Inter-storey drift and yield pattern of the members in the building hae also been studied using Pushover analysis and NLTHA and it has been found that in case of the considered dual system building, triangular distribution of pushover loads yields results closer to those obtained from the NLTHA..