Finite element analysis of inelastic behavior of structural steel beams and bridge girders

This research involves the application of nonlinear finite element methods to investigate the stability and inelastic deformation capacity of structural steel members. The computational studies are made using the finite element program ABAQUS with shell elements that include both geometric and material nonlinearities. Preliminary studies concentrate on developing techniques to accurately model the inelastic behavior of compact wide-flange beams under moment gradient and uniform moment. These modeling techniques are evaluated through comparisons of analysis results and experimental data.; Finite element analyses are performed to study the nonlinear buckling and unloading mechanisms in wide-flange beams. The effects of various restraint conditions and transverse stiffeners on the inelastic behavior are investigated. Analysis results reveal that (a) the unloading mechanism results mainly from the interaction of local and lateral buckling, (b) shifting of the neutral axis is evident as plastification and buckling occur, and (c) inelastic rotation capacity is significantly improved by continuous restraints and discrete restraints or stiffeners attached to critical sections. Also, two simplified models are proposed for predicting inelastic rotation capacity.; Strength and stiffness requirements for bracing of beams loaded inelastically are examined. The studies include the effects of various types and positions of discrete braces on the inelastic behavior of beams under various loading conditions. From the cases studied, it is shown that commonly used values for the design bracing force may not be adequate to develop the full rotation capacity of beams under uniform moment. Approximate models of the required bracing force and stiffness for beams loaded inelastically are evaluated.; The inelastic moment-rotation behavior of continuous-span bridge girders is also investigated. Verification studies confirm that the finite element modeling techniques applied for analyzing wide-flange beams are also accurate for slender web bridge girders. The influence of variations in slenderness ratios and lateral bracing on the plastic rotation capacity of girders are investigated. Analysis results also show that the locations of inelastic restraint stiffeners in the plastic hinge region greatly affect the moment-rotation characteristics. Mathematical expressions of the moment-rotation curves for girders are proposed.