Modeling of ductile fracture in steel structures for monotonic and cyclic loading

The performance of structures is greatly dependent on the material behaviour. In order to properly assess the performance, a structure has to be evaluated against a likely range of possible material behaviour. A combined experimental and numerical study has been carried out to develop procedures to generate and calibrate material model parameters to simulate the behaviour and predict fracture of steel structures and structural components under monotonic and cyclic loading. Round specimens of two steel grades with mainly three shape profiles have been tested under a variety of monotonic and cyclic loading conditions in the study. The combined isotropic and nonlinear kinematic hardening model by Chaboche has been found to be suitable for modeling the behaviour of steel based on results of the tests. A systematic procedure has been developed to determine the parameters for the plasticity model to be used in the numerical simulations. A modified Huang and Mahin fracture criterion for predicting fracture of steel subjected to monotonic tension as well as cyclic loading has also been established and validated against the test results of the round specimens.;The established procedures to calibrate and generate the material model parameters have been further adapted to study performance of a steel strap tension-only brace. The adapted procedures are able to calibrate and generate the material model parameters for the numerical simulations using only data of monotonic tension material tests when compared to and validated against results of the steel strap tension-only brace specimens tested by others. Using the validated procedures and FEA models, a parametric finite element analysis study has been carried out to study the performance of the steel strap tension-only brace for a range of material behaviour using the generated material model parameters and various geometric configurations. Based on results of the study, equations to predict the ductility of the steel strap have been proposed and recommendations on designing steel strap tension-only braces in a Seismic Force Resisting System have been developed.