Concentrically braced frames (CBFs) are stiff, strong structures, which are used for many seismic design applications. The seismic performance of CBFs varies widely because their behavior is a complex combination of resistance, elastic stiffness, and inelastic behavior and deformation. Performance-based seismic engineering (PBSE) is increasingly important. Fragility curves are statistical estimates of performance as a function of an engineering demand parameter. The Applied Technology Council's ATC-58 program is developing fragility curves for a wide range of structural systems, and this paper describes the development of fragility curves for CBF systems using experimental data that accurately simulated the boundary conditions and inelastic response of CBFs. Fragility curves were developed for common brace cross sections and gusset plate geometries at various damage states. In addition, fragility curves were developed for CBFs designed using an improved design procedure and compared to those designed using standard design methods.
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