Performance-based evaluation of the response reduction factor for ductile RC frames

Most seismic design codes today include the nonlinear response of a structure implicitly through a ‘response reduction/modification factor’ (R). This factor allows a designer to use a linear elastic force-based design while accounting for nonlinear behaviour and deformation limits. This research focuses on estimating the actual values of this factor for realistic RC moment frame buildings designed and detailed following the Indian standards for seismic and RC designs and for ductile detailing, and comparing these values with the value suggested in the design code. The primary emphases are in a component-wise computation of R, the consideration of performance-based limits at both member and structure levels, a detailed modelling of the RC section behaviour, and the effects of various analysis and design considerations on R. Values of R are obtained for four realistic designs at two performance levels. The results show that the Indian standard recommends a higher than actual value of R, which is potentially dangerous. This paper also provides other significant conclusions and the limitations of this study.