Cyclic behavior of cold-formed stainless steel sandwich tubular brace: An experimental investigation

Stainless steel shows promise for application in seismic-active regions. Previous research showed that stainless steel dampers could exhibit good energy dissipation capacity and high post-yield stiffness under cyclic loading. In light of that, a novel type of cold-formed stainless steel sandwich tubular brace (STB) is presented in this study, featuring one stainless steel square hollow section (SHS) tube as the load-carrying component and two additional stainless steel SHS tubes providing a buckling-restraining effect. Six specimens were tested under cyclic loading, varying parameters including the cross-section slenderness of the core tube, restraining ratio and loading histories. Loading protocols encompassed standardized ones following the Chinese specification (CN) and American provision (US), as well as a protocol representing the near-fault earthquakes (NF). Failure modes, hysteretic response and seismic performance indexes were obtained. Results showed that the hysteretic curves could maintain stable. Under the CN loading protocol, the specimen with a slender core cross-section exhibited uniform local buckling. The strain hardening coefficient omega stayed within the range of 1.46-1.58. The specimens exhibited a slow decay rate of tangent stiffness, highlighting their relatively high post-yield stiffness. The cumulative energy dissipation factor could reach 658, signifying good energy dissipation capacity. Additionally, under NF loading, specimens exhibited enhanced cumulative ductility compared to CN or US loading. Furthermore, an evaluation was conducted to assess the suitability of existing design methods for preventing overall buckling and local bulging in stainless steel STBs. It indicated that the current design approaches tended to be overly conservative for both overall and local stability design of stainless steel STBs, primarily due to the lack of consideration for SHS core stiffness and the interactions between flanges and webs, respectively.