Strain Life Analysis at Low-Cycle Fatigue on Concentrically Braced Steel Structures with RHS Shape Braces

The seismic performance of concentrically braced frame systems, with braces designed in order to buckle inelastically under a severe earthquake loading, mainly depends on the hysteretic response of the steel braces. As observed in past earthquakes and in experimental programs available in the literature, rectangular hollow section shape braces are more susceptible to early fatigue failures compared to other section shapes. This research, in particular, is focused on the evaluation of the hysteretic response of rectangular hollow section shape braces through appropriate low-cycle fatigue model implemented in a fiber-based element computer program. Firstly, the main influence regarding the number of integration points, number of subdivisions for single brace members, and initial camber on the local response of fiber-based inelastic beam-column element models based on force formulation is investigated. Secondly, the peak strain distribution is used to calibrate the input parameters of the low-cycle fatigue material model. Several data obtained from past experimental programs developed at the Universities of Montreal, Washington, and Calgary are also considered. Finally, an eight-story steel building is designed in order to evaluate the performance levels through incremental time history analyses.