Design of Gusset Plates and Interface Welds of SCBF Systems with Braces Buckling In-Plane

Abstract

The design of connections of gusset plates, beams, and columns of concentrically braced frame systems is typically based on the forces generated by brace actions without considering the frame actions. This may result in underestimating the design force demand on gusset plates, potentially leading to the failure of interface weld connections at higher lateral drift levels. The present study aims to estimate the force demands at the connection interfaces, typically about a 2% story-drift ratio (SDR), corresponding to the design-level ground motions for braced frame systems. The study considers both the forces of frame and brace action on the corner gusset plate in the design process. It also aims to develop suitable design recommendations to prevent premature weld failures at higher lateral drift. High-fidelity finite-element models of in-plane buckling (IPB) braced frame systems are developed and analyzed under various loading modes. A current standard design method to determine the interface weld size was found to be inadequate to prevent premature failures at the higher drift levels. This is primarily due to the accumulation of the plastic strain at the tip of the gusset at higher drift. The out-of-plane bending of the gusset plate due to geometric imperfection was also found to contribute toward the development of high plastic strain at the tips of gusset plates. Three different connection configurations are considered and analyzed under critical cyclic loading conditions. Finally, design recommendations are presented to avoid stress concentration and premature fracture of gusset plate connections of the IPB braced frame systems.