Numerical Simulation of Inelastic Cyclic Response of Hss Braces Upon Fracture

Concentrically braced frames (CBFs) with a tension-compression bracing system dissipate hysteretic energy when braces yield in tension and buckle in compression, whereas the hysteretic response of hallow structural section (HSS) braces varies with brace slenderness, width-to-thickness ratio, and yield strength. Modelling the nonlinear response of braces upon the fracture requires an assigned brace fracture model and implicitly calibrated input material parameters. The selected brace fracture models are those that are compatible to nonlinear analysis and fiber-based elements formulation suited to OpenSees framework. To replicate the brace response, nonlinear beam-column elements that encompass distributed plasticity and discretized fiber cross-sections were used, whereas to simulate brace fracture, the strain fatigue model was considered. In this study, in order to predict the failure strain for a single reversal value that is required as input parameter in the strain fatigue model, regression analysis was employed and the proposed equation was given for square HSS braces and validated against experimental test results for a wide range of brace slenderness ratios, 50 kL/r 150 and types of displacement loading history. The predicted failure strain value is expressed in terms of slenderness ratio, width-to-thickness ratio and yield strength of steel. Comparisons to existing brace fracture models, such as the strain-range and end-rotation of braces at fracture, are provided. All aforementioned brace fracture models were evaluated against experimental tests results, while replicating fourteen specimens that were found in the literature.