Seismic performance of knee-braced frames equipped with NiTi BRBs

Abstract

Knee braces (KBs) are often installed at locations near to the beam-to-column connections in frames. In comparison to concentrical and eccentrical braces, KBs have advantages of occupying less space, less affecting the architectural view, and ease of installing and replacing if necessary. As a comparative analysis, this paper evaluates the seismic performance of knee braced frames (KBFs) equipped with steel or NiTi buckling-restrained braces (BRB). Through machining raw bars into bamboo shape, this paper fabricated two types of KBs and conducted cyclic loading tests on reduced-scale specimens. The testing results show that both KBs have stable cyclic properties under loading reversals. The steel BRB has typical elasto-plastic hysteresis, whereas the NiTi BRB has a flag-shape hysteresis. At the system level, the 3- and 6- story KBFs were first designed by performance-based plastic design (PBPD) method and then subjected to a suite of earthquake records. It indicated that the KBFs equipped with either steel or NiTi BRBs can well meet the prescribed drift target. The major advantage of NiTi BRBs over steel BRBs is that they successfully eliminated residual drift ratios for the protected frames, which means the KBFs with NiTi BRBs have higher seismic resilience.