DYNAMIC RESPONSE OF AN UNSYMMETRIC 28 STOREY BUILDING

Abstract

The objective of present work is to. study dynamic response of irregular multistory building. Twenty-Eight story building (height of 135 m) having plan and elevation irregularity have been designed as per Indian Standards. Thirty two different load combinations have been considered while designing the building. Model was prepared with and without accidental torsion, strong column weak beam concept. Response spectrum analyses have been carried out for seismic analysis of buildings. Building was considered in Zone-III and was checked for high intensity earthquake. The actual behavior of building can't be predicted unless we do nonlinear analysis. So the best tool to predict non linear behavior of building, static non linear analysis or Push over analysis is used which is a performance based analysis of a building. Pushover analyses have been carried out for Zone-III to study the demand capacity of building and found out that when building is encountered with high intensity earthquake its performance reduces and building reaches towards collapse. It has been found out that maximum inter-story drift for any story was ( 0.1 %) and maximum top deflection was ( 0.215 m). Also stories with inclined columns are showing more inter-story drift as compare to building with vertical column which were found within permissible limits of IS-1893 but designer must give due attention towards such drifts while providing inclined columns in multistory buildings. The building with inclined column and ring beam forms an exterior tube which produces higher torsional rigidity to the building. Also due to horizontal and vertical irregularities in building, huge amount of torsion encounters which causes change in longitudinal reinforcement in outer periphery column. Thus the better suggestible tool to counteract with such problem is to keep center of gravity and center of rigidity of building near as far as possible. ETABS v9.5.0 is a sophisticated special purpose analysis and design program developed specifically for multistory building systems. Also the validity of ETABS to model sophisticated building components such as ramps, inclined columns with tapered section has been checked and found out that it works well with all such components too.