Evaluation of Response Reduction Factor of RC Framed Buildings by Pushover Analysis

Vulnerability of buildings to seismic hazards is more drastic in developing countries with high seismicity, as compared to developed countries which is primarily due to the lack of seismic design guidelines. Response Reduction Factor (R) is an essential seismic design tool, which is typically used to describe the level of inelasticity expected in structure during an earthquake. The concept of R factor is based on the observations that well detailed seismic framing systems can sustain large inelastic deformations without collapse through excess of lateral strength over design strength and ductility. Developed countries like United States and Europe, defining R factor with component wise like over strength factor and redundancy factor. Where as in IS 1893 (Part-II) 2002, the R factor which is arrived at empirically based on engineering judgment and perceived earthquake damage with little technical basis. This research focuses on estimating the actual value of R factor of RC framed buildings designed and detailed following the Indian standards and comparing these values with the value suggested in the Indian code. The main focus of this study is to evaluate component wise computation of R factor and effect of number of storeys on this factor using Pushover analysis. Performance level considered in this study is corresponding to global performance level (at 2% storey drift) and local performance level (life safety level) whichever occurs first. From this study, it was found that Indian seismic code giving conservative R value for regular RC framed buildings as per considered performance level. Also found that overstrength factor is decreasing and ductility factor is increasing as the number of sroreys increases. Keywords- Response reduction factor, Over strength factor, Ductility factor and Pushover analysis