11.45: Cyclic testing on hybrid buckling‐restrained Braces (HBRBs)

ABSTRACT Buckling‐restrained braced frames (BRBFs) are dependable lateral load‐resisting systems to safeguard buildings against seismic actions. Nearly‐symmetric and stable hysteretic response of buckling‐restrained braces (BRBs) stimulated the wide spread incorporation of BRBFs in various structural systems. However, BRBFs suffer from increased drift demands as compared to other braced frame systems, mainly due to the low post‐yield strength/stiffness of BRBs. This study proposes a hybrid buckling‐restrained brace (HBRB) combining the short yielding core BRB (SBRB) and a heavy elastic hollow steel section (HSS) in series. SBRB is allowed to undergo desired level of plastic deformation, whereas the elastic HSS segment can provide the improved stiffness to the HBRBs. Such HBRBs have similar, stable and balanced hysteresis and enhanced elastic and post elastic stiffness as compared to conventional BRBs. In this study, three reduced‐scale models of proposed HBRBs with varying yielding lengths are fabricated and sub‐assemblage tests are carried out under modified non‐linear reversed cyclic loading conditions. For the buckling‐restraining of SBRB segments, concrete filled detachable casings with all‐around end cover plate arrangement is used, whereas a rigid connection between the SBRB and HSS is considered. Results showed that HBRBs were capable of withstanding an axial core strain of more than 6% without any instabilities. Further, HBRBs exhibited excellent hysteric response, load‐resisting capacity, deformation ductility, and hysteretic energy dissipation potential. Strength‐adjustment factors of HBRBs are also found to be little larger than those of conventional BRBs.