Ductility demand on short-length buckling restrained braces in concentrically braced frames

Abstract

Steel concentrically braced frames (CBFs) suffer from the strength and stiffness degradations due to the compression buckling of conventional braces during the seismic events. Low-cyclic fatigue fractures associated with these buckling-type braces (BTBs) also reduce the overall ductility of CBFs. In contrast, buckling-restrained braces (BRBs) having symmetric hysteretic response can contribute to the improved energy dissipation and the superior ductility potential prior to fracture. However, the relatively smaller brace stiffness and the preferred pinned connections in buckling-restrained braced frames (BRBFs) results in the increased drift demand that may adversely affect the retrofitting and reusability of the structures after the earthquake. A hybrid brace having a combination of an elastic BTB segment and a yielding short length BRB (SLBRB) segment in series can increase the lateral stiffness of BRBFs, which can reduce the drift response by maintaining the symmetric hysteresis. This may result in the increase in ductility demand in the SLBRB segments of the hybrid brace in proportion with the decrease in the yield lengths. This study is encompassed on the determination of ductility demand requirements in a 3-story braced frame fitted with the hybrid braces arranged in the chevron configurations. Non-linear static and dynamic analyses are conducted on hybrid braced frame (HBF) as well as BRBF. The results of drift response and maximum ductility demand of HBF and BRBF are discussed.