Improved Seismic Performance of Gusset Plate Connections

Abstract

Current design practices use a strength-based design approach to design gusset plate connections in special concentrically braced frames (SCBFs), in which the expected tensile and compressive capacities of the brace are used to design the gusset plate and the weld used to connect the brace to the frame. To achieve brace end rotation, the gusset plate is sized using a linear offset rule, and large, uneconomical gusset plate connections may result. A research program was undertaken to improve the economy and performance of gusset plate connections. A new approach is proposed in which the gusset plate design is based on a balanced design approach in which the yield mechanisms of the brace are balanced with the yield mechanisms of the connection and the failure modes of the system to achieve a target yielding hierarchy and suppress unwanted failure modes. Full-scale one-story, one-bay frames were designed and tested to investigate the seismic performance of current and proposed design methods. In the test program, variations in balance factors between the brace, gusset plate, and weld were considered to study the proposed method, to evaluate possible yield mechanisms and failure modes, and to obtain the desired yielding hierarchy. Comparison of the observed and measured performance of each specimen is made and specific design expressions to improve the seismic engineering of SCBF systems are proposed.