Parametric study on the I-shape brace connection of conventional concentrically braced frames

Abstract

Concentrically braced frames (CBFs), designed using the conventional linear elastic method without seismic proportioning and detailing requirements, are referred to as Conventional CBFs (CCBFs) in this study. They are widely used in moderate and low seismic areas in North America due to the ease of design and economy. Without a code specified dedicated fuse member to dissipate earthquake induced energy, or a prescribed yield/failure hierarchy, the brace connection of a CCBF is usually the weakest link in the lateral load-carrying path and prone to fracture. The brace connection is therefore determinant for the structural seismic performance. In this paper, a parametric study based on a validated numerical simulation procedure was carried out on a typical I-shape brace connection, i.e. the flange plate connection. Three key design parameters, namely, the gusset plate thickness, the flange lap plate thickness, and the web lap plate thickness, were varied to study their effects on both the compressive and tensile behaviour of the brace and connection assembly. Various possible failure modes were revealed both in compression and in tension. The results showed that the brace end restraint provided by flange plate connections in CCBFs was significant; the pinned-end assumption would lead to conservative estimation of the brace buckling resistance, which might trigger detrimental gusset plate buckling. The tensile overstrength of the flange lap plate, due to the presence of transverse tensile stress along the net section, was quantified using the von Mises criterion. Design recommendations are proposed with regards to attaining better deformation capacity.