Influence of connection design on the inelastic seismic response of HSS steel bracing members

The design of brace connections for concentrically braced steel frames detailed for ductile inelastic seismic response is examined. The study focuses on bracing members made of square hollow structural steel shapes with welded slotted connections. Different design strategies are investigated to prevent net section fracture and develop the full tensile capacity of the braces. Connections designs for out-of-plane and in-plane buckling of the braces are also proposed and discussed. The response of a brace sample subjected to monotonic loading as well as under quasi-static cyclic displacement history is examined through detailed finite element analysis. Un-reinforced brace connections are found to be prone to premature fracture under tension, especially when defects are present along the slots cut in the tube walls. Connections designed for out-of-plane and in-plane brace buckling resulted in nearly identical cyclic inelastic brace response. For the out-of-plane buckling design, satisfactory brace end rotation responsewas achieved without the free length gusset plate detail proposed in codes.