Hybrid buckling-restrained braced frames

In Performance Based Earthquake Engineering (PBEE), various limit states should be satisfied at different levels of ground motions. Current design practice mostly focuses on the Life Safety (LS) or Collapse Prevention (CP) limit states, and neglects the possible excessive damage that occurs under frequent low to mid intensity ground motions. This paper investigates a hybrid Buckling-Restrained Braced Frame (BRBF) where the steel core of the brace is made of different steel types including carbon steel, High Performance Steel (HPS) and Low Yield Point (LYP) steel. The LYP component of the steel core yields earlier than the structural steel and the energy dissipation associated with the early yielding helps the hybrid BRBF to perform better than the traditional BRBF under low to mid-level earthquakes. Since the low post-yield stiffness of the Buckling-Restrained Braces (BRB) may cause BRBFs to exhibit large maximum and residual drifts, high strength steel is also used in the steel core to provide strength and high stiffness under large drifts. The use of high strength steel enhances the performance under Design Basis (DBE) or Maximum Considered (MCE) type earthquakes. In this paper, Nonlinear Static Pushover (NSP) and Incremental Dynamic Analysis (IDA) are conducted and comparisons between the hybrid and the traditional BRBFs are made. Conclusions regarding the advantages of the hybrid system are presented.