This report describes simulations of the inelastic seismic behavior of steel braced frames, including the effects of low-cycle fatigue. For steel braced frames under complex loading conditions, a wide variety of behavior mechanisms and failure modes may occur for each type of member and connection. Thus, numerical models that assess the initiation and propagation of failure during cyclic loading need to account for multi-axial states of material nonlinearity, local and global buckling and the exhaustion of the ability of the material to deform inelastically caused by low-cycle fatigue.
Following a review of existing material models for simulating structual steel deterioration, a series of investigations are conducted using finite element modeling techniques. A new, numerically efficient continuum damage mechanics material model capable of simulating inelastic behavior and deterioration of mechanical properties because of low-cycle fatigue has been devised and implemented in a finite element sofware LS-DYNA. Computational results obtained with this new material model correlate will with test results for several beam-to-column connections, individual braces, and braced frame subassemblies. Recommendations for characterizing material properties for these types of analyses are developed and presented. A series of analyses are presented that evaluate and refine several requirements for detailing and analyzing special concentrically braced steel frame buildings.
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