Cyclic tests on hybrid buckling-restrained braces with Fe-based SMA core elements

Abstract

The present study is focused on the development and testing of a novel buckling-restrained brace (BRB) system. The Fe-based shape memory alloy (FSMA) plate is used as the yielding core segment, whereas the steel plates are adopted in the fabrication of the elastic end segments as well as the buckling-restraining systems. As a proof-of-concept, a miniature BRB with extruded FSMA core was tested under quasi-static loading to explore its force-resisting capacity, displacement ductility, and the energy dissipation potential. Five full-scale brace sub-assemblages were fabricated using the short-core FSMA BRBs (named as, FSBRB) and the elastic hollow tubular members. The short-length FSMA yielding core plates were welded to the steel elastic segments of BRBs. Four hot-rolled steel angle sections were used to fabricate the buckling-restrained mechanism for the short-core BRBs. All brace sub-assemblages were subjected to reversed-cyclic gradually increasing displacements as per ANSI/AISC 341–16 loading protocol. The main parameters varied in this study were the length of FSMA core plates, the size of the air gap between the core plates and restrainers, the position of stoppers, and the detailing of welding connections between the FSMA core plates and the elastic steel segments. All brace sub-assemblages exhibited stable and nearly symmetric hysteretic response and excellent cumulative displacement ductility. Though the heat-affected FSMA plates exhibited a considerable reduction in the strain capacity, the proposed detailing scheme resulted in the better strength-adjustment factors and the displacement ductility of the FSBRB specimens.