Effect of brace failure as capacity-based design component on the EBF collapse safety

Abstract

Eccentrically braced frame (EBF) is considered a suitable seismic resisting system in terms of its high ductility, and stiffness simultaneously. In this frame, nonlinear behavior and energy dissipation are limited to link beam, and other members (capacity-designed members) are designed in proportion to maximum link shear force. Despite the significance of capacity-designed members, their reliability evaluation and the effect of their failure on the overall behavior of EBF have not been studied in prior research. The aim of this paper is to evaluate the effect of brace failure on the probability of collapse by considering system overstrength, varied ratios of the capacity to demand factors (ϕ/γ) in brace design, and seismic hazard curve. To achieve this aim, Incremental Dynamic Analysis (IDA) was used to study nonlinear structural models of EBF, evaluate the force demands on the braces, and the effects of brace failure on the system collapse. The reliability analysis was performed by integrating the viewpoint of LRDF component design with the FEMA P695 system reliability methodology. The results indicate that the probability of total collapse increases significantly at low spectral acceleration due to brace failure. Additionally, the appropriate value of ϕ/γ in brace design can be calculated for different seismic areas and system overstrength to ensure an acceptable margin of collapse safety.