Inelastic Large Deflection Modeling of Beam-Columns

Abstract

Linear structural analysis is incapable of reflecting the real behavior of a structure under abnormal or ultimate loading conditions. When deformations are large and a structure behaves nonlinearly, the stiffness of the structure changes even if the structural material shows a purely linear elastic behavior, and a geometric nonlinear analysis or a second-order elastic analysis should be performed. However, under severe environmental loading such as strong wind or earthquake, there is a need for a direct second-order inelastic 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 inelastic and large deformation analysis of planar steel structural systems. Derivations of the different stiffness matrices that are used in the new models are presented. Both models have the capacity to account for residual stress consideration. The new model satisfies the rigid-body test, while the second model does not. The accuracy of the two models is compared with benchmark problems via three examples. The results indicate that the new model is more robust and has a faster rate of convergence for problems involving inelastic behavior, high stress, and large deflections.