Experimental and Analytical Investigations of Net Section Fracture in Brace-Gusset Plate Connections

In recent years, braced-frame construction has gained considerable popularity for lateral load resisting systems in regions of high seismic activity. Concentrically Braced Frames (CBFs) have been one of the more prominent systems in this classification, relying on the inelastic cyclic buckling and yielding to resist seismic loads and dissipate energy. During tensile cycles, the brace places large demands on the brace-gusset plate, and in turn the gusset plate-beam or column, connections. While failures in this region have not been observed in previous earthquakes, studies suggest that net-section fracture may be a potential mode of failure in these connections. This paper focuses on investigating the inelastic seismic response of typical slotted net section connections of hollow structural sections (HSS) and round pipe under earthquake type monotonic and cyclic loads. Specifically, experimental observations from a Network for Earthquake Engineering Simulation and Research (NEESR) project on nineteen large-scale bracing members in the context of net section performance are presented. In addition to providing insights into behavior, the experiments also serve to validate micromechanics-based modeling approaches that predict ductile fracture. One such approach, utilizing the Void Growth Model (VGM) is discussed and presented as an analytical and general alternative to costly experimentation.