ASSESSMENT ON EFFECTS OF INFILL WALL AND MASS IRREGULARITY ON SEISMIC RESPONSE OF BASE ISOLATED BUILDINGS

Abstract

Irregularities are inevitable in the architectural design of a building and there is a gap in the literature on seismic response behaviour of a structure with infill and mass irregularity with base isolation. This thesis work presents a numerical investigation on seismic response of effect of wall infill and mass irregular reinforced concrete (RC) base-isolated buildings under linear dynamic analysis. Validation analysis is performed using results reported in literature followed by response spectrum (RS) dynamic analysis of a base-isolated seven story RC building with various infill and mass configurations using the ETABS structural analysis software program. In this study, lead rubber and linear natural bearing base isolators are used at the corner and the middle of the plan respectively. Due to the existence of the lead core, LRB provides high damping by deforming plastically when the isolator moves laterally in an earthquake and LNR has low damping performance, excellent linearity, and stable restoring force characteristic. Results of this research indicated as compared to bare frame, fully infilled models exhibited 19.9% and 10.48% reduction of lateral displacement and storey drift, respectively. Similarly, In the mass irregularity model M1, the displacement reduced by 20.9% and 20.23%, the story drifts reduced by 48.3%, and 42.9% (both x and y direction) respectively compared to the M3 mass irregular model. In addition, in the combined irregularity models M2IF2 and M2IF3, the story displacements, and the story drifts are reduced both in x and y directions as compared to the M2 mass irregular model. Overall, seismic performance of RC framed structure is significantly increased with the application of infill walls, and removing infill walls from a ground story leads to soft story occurrences and makes a structure vulnerable to collapse.