A ductile fuse for special concentrically braced frames

Abstract

In special concentrically braced frames, brace yielding and buckling are the primary mechanisms of seismic energy dissipation, and mid-length brace fracture is the preferred failure mode. However, as evidenced by several studies, the connections between the braces and gusset plates are susceptible to premature fracture as are other connections e.g. between the gusset plate and beam or column. This paper describes the preliminary development of a simple ductile fuse to prevent such failures. The fuse is created by selectively reducing the brace material strength through a thermal treatment process which in turn reduces connection force demands. Material testing of ASTM A500 steel from square HSS tubing was conducted to characterize the mechanical property changes from the thermal treatment and to calibrate 3D finite element (FE) models of brace members. The experimental data and FE models demonstrate the benefits of the fuse, which include, reduced tensile force demands at the brace to frame connections, improved fracture resistance of brace material, increased drift capacity, residual stress relief and improved element compactness.