Inelastic large deflection modeling of beam-columns

Linear structural analysis is incapable of reflecting the real behavior of a structure under abnormal or ultimate loading conditions. When deformation s are large and a structure behaves nonlinearly, the stiffness of the struc ture changes even if the structural material shows a purely linear elastic behavior, and a geometric nonlinear analysis or a second-order elastic anal ysis should be performed. However, under severe environmental loading such as strong wind or earthquake, there is a need for a direct second-order ine lastic analysis to calculate the ultimate strength capacity and to predict the true behavior of structures. This paper presents and compares two beam- column models, both based upon fiber-type, beam-column elements, for inelas tic and large deformation analysis of planar steel structural systems. Deri vations of the different stiffness matrices that are used in the new models are presented. Both models have the capacity to account for residual stres s consideration. The new model satisfies the rigid-body test, while the sec ond model does not. The accuracy of the two models is compared with benchma rk problems via three examples. The results indicate that the new model is more robust and has a faster rate of convergence for problems involving ine lastic behavior, high stress, and large deflections.