Assessment of Response Reduction Factor for Reinforced Concrete Frame Buildings in a Probabilistic Seismic Risk Framework

Abstract

Response reduction factor (RRF) was first introduced in 1978 NEHRP provisions. These factors split the earthquake-resistant design process into two independent segments—first, quantification of the actual seismic demand assuming that structure remains elastic during the expected level of excitation and second, prediction of reserved capacity of a structural system. The RRF values were largely assigned with the intent to avoid significant deviation in the prevalent design base shear due to modifications in the code. For regions of moderate seismicity, selection from the alternatives of constructing a limited-ductile building or a fully ductile building is governed by the cost of material and execution. Ideally, the two available choices for the structural systems should result in similar building performance levels. Extending this requirement in a probabilistic seismic risk framework, the paper presents the quantification of RRF values for both alternative structural systems. The results obtained from sample midrise reinforced concrete moment-resisting frame (RCMRF) building located in Mumbai and designed as per Indian standards have been presented. It is found that both variants exceed their respective RRF values assumed by the code. It is also found that the fully ductile building offers better performance level than the limited-ductile building. The results have implications for the specification of RRF in the current Indian standards.