Seismic response of moment resisting frame with open ground storey designedas per code provisions

Abstract

Urbanization, functional requirements and paucity of space have led to multi-storey building having open ground storey. During the past earthquakes, open ground storey buildings have performed poorly due to the soft storey defect. Indian Standard 1893 Part 1 (Indian standard criteria for earthquake resistant design of structures, 2002) allows analysis of open ground storey buildings without considering infill stiffness but with a multiplication factor (MF) 2.5 in compensation for the stiffness discontinuity. The aim of this study is to check the applicability of the multiplication factor of 2.5 and study the behaviour and response of the structure. Investigations were carried on reference bare frame model without considering infill stiffness as suggested by IS 1893 (Indian standard criteria for earthquake resistant design of structures) using SAP 2000 (Version 14.0) by linear static analysis and response spectrum analysis. Total seven models were analysed and designed with multiplication factor ranging from 1.0 to 2.5. From the results, it is observed that the value of MF equal to 2.5 has been found on the higher side, resulting in increased dimension and percentage of reinforcement of ground storey columns without significant enhancement beyond a certain MF. The best possible rectification measure, when the stiffness of the infill is not considered, is to multiply the ground storey columns by 1.25 factor instead of codal value of 2.5. Using higher values of MF results in the introduction of soft storey effect in the upper storey.