Site Specific Response Analysis of High Rise & Low Rise Buildings

Abstract

Earthquakes are natural hazards under which disasters are mainly caused by damage or collapse of buildings and other man-made structures. During an earthquake, seismic waves radiate away from the source and reach the ground on which these seismic waves produce shaking. The surface ground shaking causes severe damage to the structures, which depends on characteristic of subsurface soil. The seismic force on building depends on peak ground acceleration and time period of building as specified in IS: 1893 (Part I)-2002 in terms of zone factor (Z) and spectral acceleration (Sa/g). Codal provisions usually specify standard normalized response spectra for different soil types irrespective of local conditions. Therefore for a realistic design of earthquakeresistant structures site-specific detailed investigation is necessary.

In the present study ground response analysis of eleven sites of Ahmedabad city is carried out using one dimensional equivalent linear analysis. Site specific response spectra are developed using ProSHAKE software. ProSHAKE is a software based on widely adopted one dimensional geotechnical site response model. Acceleration time history recorded at Passport office building of Ahmedabad on 26th January 2001 Bhuj Earthquake is considered as input motion for different sites to get acceleration time history of ground as well as response spectra. The site specific response spectrum for various sites are then compared with the standard response spectrum plot given in IS: 1893 (Part I)-2002.

The site specific response spectra are used to evaluate response of multi-storied frame structures using ETABS software. The base shear is calculated for 3 to 20 storied regular frame structures for various sites. Also shear forces, bending moments and axial forces for ground floor columns of the structures are obtained using site specific response spectra. The analysis result of site specific response spectrum analysis is compared with that obtained considering IS: 1893 (Part I)- 2002 response spectrum. Design for two multi-storied frame structures is carried out.

From the analysis results it is observed that site specific response spectrum analysis gives higher seismic force for low rise buildings while lower seismic force for high rise buildings resting on soil strata considered for study.