Replaceable fuse buckling-restrained brace (BRB): Experimental cyclic qualification testing and NLFEA modeling

Abstract

Building in seismically active regions subjected to lateral forces requires adequate strength and stiffness to resist such forces. Numerous studies have shown that braces perform better against axial loads than conventional braces if inhibited from buckling with a restraining mechanism. This system is called Buckling Restrained Braces (BRBs), enhancing energy dissipation when added to a structure. Contrary to the conventional BRBs, this paper presents testing a newly patented type of BRB system consisting of a stainless-steel core bar inserted into a buckling inhibiting unit made of mild steel pipe filled with grout and connected to a novel end restrained unit so-called fingers. The new system provides easy replacement of the core (dissipation unit) and end units if replacement is needed after a significant seismic event. Six BRB samples of three different cross-sections of core units were subjected to uniaxial cyclic loading following the AISC 341 qualification testing protocol. Only full-threaded core and smooth shaved core bars passed the qualification test out of three cross-sections. The successful tests showed a stable hysteretic response in the tension and compression phase of loading and a significant ductility of µ=4. Overall load-deformation responses, ductility, overall stiffness, and energy dissipation were analyzed and compared for the BRBs tests. The threaded cross-sectional type of core bar showed the highest energy dissipation and attained ductility compared to the other types of tested bars. A 3D NLFEA model of the best performing BRB specimen was created using the commercial software package ABAQUS. It exhibited notable agreement with the experimental results. The produced high-fidelity NLFEA models are a solid basis for a future more comprehensive parametric investigation campaign.