Response modification factors of buckling-restrained braced frames designed according to the Egyptian code

Abstract

Over the past two decades, buckling-restrained braces (BRBs) have become increasingly popular as a lateral resisting system because of their capability to provide energy dissipation, stiffness and strength to building structures. Up to date, the Egyptian code has no specifications for estimating the response modification factor (R-factor) of structures equipped with BRBs. The only available alternative for BRB design is to use the R-factor of conventional bracing which is equal to 4.5.This study evaluates the R-factors of low– to mid-rise buckling restrained braced frames (BRBFs) designed according to the Egyptian code. Three BRBFs with 3-, 6- and 12-stories are designed with an R-factor of 4.5. The actual R-factors of the frames are evaluated by conducting static pushover and earthquake time history analyses. The results obtained indicate that the R-factors of the BRBFs considered in this study vary from 5.0 to 13.5 in case of static pushover analysis and from 6.7 to 9.1 in case of earthquake analysis. These static and dynamic ranges of the R-factor are higher than the R-factor of 4.5 specified by the Egyptian code for the design of braced steel frames. Keywords: Buckling-restrained brace, Response modification factor, Egyptian code, Pushover, Earthquake