Multiaxis Hybrid Simulation of Collapse Resistant Buildings with Ductile Soft Story Formed by Concrete-Filled Steel Tube Columns

Abstract

A widespread problem in regions of low to moderate seismicity is the failure of buildings with soft-story collapse mechanisms. A reliable approach to improve the design of such buildings is to use concrete-filled steel tube (CFT) columns to form a ‘ductile’ soft story to arrest damage at the first level. This can perform as an isolator to limit the damage and prevent it from spreading to the rest of the building. In this paper, the multiaxis hybrid simulation method is used to evaluate the three-dimensional response of CFT columns while they serve as part of a building developing ductile soft first story mechanism. For this purpose, the multiaxis substructure testing (MAST) system at Swinburne University of Technology was utilized to simulate realistically the time-varying multi-directional boundary forces generated by ground motions on the CFT columns. The circular and square cross-section shapes as the most popular type of CFTs were tested and the damage progression, global hysteretic behavior, and deteriorating mechanisms were studied. The obtained data were then used to conduct a fragility analysis to compute the risk of collapse. The results highlight the excellent performance of CFTs and their potential to construct low-damage collapse resistant buildings.