Seismic capacity quantification of gusset-plate connections to fracture for ductility-based design

This paper presents an experimental study on the seismic performance up to fracture of gusset-plate brace connections. During the inelastic behavior of a bracing member (e.g., buckling), weak-axis bending in the gusset is induced by brace-end rotation and a plastic hinge is formed in a predefined inelastic zone (clearance distance) of the gusset. Five gusset-plate connections that can develop restraint-free plastic rotations to accommodate the brace-end rotation demands are tested. The test parameters include the plate thickness, length of clearance distance, and several inelastic rotation demands. The connections are tested using an innovative substructure-based hybrid test method that simulates the complex boundary and load conditions that exist between the gusset-plate connections and brace member. The tests quantify the maximum rotation ductility and strength capacity of the gusset-plate connections under actual cyclic inelastic rotations and varying axial loading. The test results also provide a basis for developing a ductility-based design methodology that determines the rotation ductility of gusset-plate connections using the brace-end rotation demand at a given axial deformation capacity of the brace. A design application example demonstrates the necessity of considering explicitly in the seismic design of steel braced frames the gusset-plate fracture capacity.