Modeling of local buckling in tubular steel frames subjected to cyclic loading

In this paper, a model of the behavior of metallic structures subjected to flexural effects is proposed. The model focuses on the description of failure due to local buckling. It is assumed that the main inelastic phenomena involved in the process: plasticity and local buckling, can be lumped at inelastic hinges. The model takes into account that in planar frames, two local buckling can appear in the plastic hinge region: one due to a positive moment the other one related to a negative moment. The elastic behavior of frame members with two local buckling is assumed as unilateral. The plastic behavior is described using the concept of equivalent moment on a damaged plastic hinge. A new hypothesis, that authors have called “counter-buckling”, is introduced. The counter-buckling concept states that as a consequence of the evolution of one local buckling, the other one results partially blocked. The notion of counter-buckling is used to describe local buckling evolution during cyclic loadings. Finally, the model is verified through the numerical simulation of several experimental tests on frame members and framed structures.