Seismic Response Modification Factor of RC-Frame Structures Based on Limit State Design

Abstract

The main objective of this research study is to evaluate the response modification factor, R, of moment-resisting RC-frame structures that are designed based on a limit state design methodology. The study is focused on the ordinary and special RC-frames of 1, 2, and 3 bays at 3, 5, 7, and 9 stories. To evaluate the R-factor of each frame structure, a nonlinear static pushover analysis is performed and the capacity curve of structure until a maximum lateral displacement that is typically prescribed by seismic design codes is plotted. Results of this study indicate that the R-factor is significantly influenced by the number of stories and bays, as well as the maximum lateral displacement that is imposed on structure during pushover analysis. The pattern of variation in R-factor with an increase in the number of bays or stories is evaluated herein this paper. The values obtained for R-factor in ordinary and special frame structures are compared with the corresponding values prescribed by current seismic design codes including European Standard EC8, International Building Code (IBC), ASCE 7, National Building Code of Canada (NBCC), and Iranian Standard 2800-91. Based on the minimum values evaluated in this study, the design R-factor of ordinary and special RC-frame structures may be rounded to 3 and 7, respectively.