Finite element modeling of the inelastic cyclic response and fracture life of square tubular steel bracing members subjected to seismic inelastic loading

摘要

Realistic modeling of complex nonlinear behaviour and potential failure of steel braces attributable to Ultra-Low Cycle Fatigue (ULCF) is necessary to accurately assess the seismic performance of steel braced frames. Recently, micromechanical models capable of predicting the earthquake-induced ULCF have been developed. This paper presents an in-depth simulation of test results and detailed evaluation of the available local micromechanical models on predicting the initiation of crack under ULCF loading regime. Five HSS steel braces with square cross-section that were recently tested were selected for the study. The braces have 4 to 6 meters in length; have slenderness ratios of 40 and 60, and width-to-thickness aspect ratios of 17 and 24. Cyclic hardening parameters used in the models have been obtained from monotonic and cyclic coupon tests. The refined Cyclic Void Growth Model (CVGM) that can predict the initiation of crack in ductile fracture is employed and the analysis results are presented. Modeling techniques and the selection of the influencing parameters in the utilized finite element models including the cyclic hardening parameters are explained in this paper. Models simulated the overall and local behaviour of the specimens including the instance and the location of ductile fracture, after the onset of local buckling where the strain demand raised and the plastic hinging formed. These analyses are computationally expensive; however, the models are capable of predicting the observed brace behaviour under the applied loading regimes featuring the potential for extending the results to a range of braces with different geometric dimensions.