Seismic Design Model of Special Concentrically Braced Frames with Balance Factors

Reliable seismic performance requires a structural system that can withstand multiple inelastic displacement cycles at large drifts. The response of a steel frame systems is largely dependent on the inelastic deformation capacity of the frame members. Recent studies on the seismic performance of moment-resisting frames have shown that limited yielding is allowed at connections including beams, and that improved behavior, including increased ductility, can be achieved when the resistance of these yielding mechanisms is properly balanced. The adverse effects of premature failure are controlled by balancing the failure modes and the yielding mechanisms. This paper aims to improve the seismic response of a concentrically braced frame system by presenting a design methodology that balances the yielding mechanisms and the failure modes. Using past experimental results, an improved design model for braced frame gusset plate connections is developed and preliminary estimates of the required design parameters are provided.