Effect of the Post-Peak Behavior on Collapse of Structural Systems

Simulation of structures under collapse requires accurate prediction of extreme limit states associated with material (tension necking) and/or global (buckling) instabilities. While spring or hinge models, fiber models, and continuum finite element models have been used to evaluate the behavior of a collapsing structure, each of these methods have definitive drawbacks when attempting to simulate the post-peak behavior. An alternative method is proposed in this paper, which consists of a one-dimensional single line element that includes the effect of localization. Cylindrical steel samples of different lengths were tested in tension and their response recorded with a DIC system to evaluate the evolution of localization. The experimental data were then used to develop a simplified one-dimensional line element that can capture the effect of localization on the overall post-peak structural response to tension. The proposed model defines the pre- and post-peak stiffness of the line element, respectively, through a quad-linear curve. Of particular importance is the introduction of the bifurcation point which defines when unloading in the member occurs. This tension model was employed in a simple truss structure to evaluate its effectiveness in evaluating the post-peak response as compared with other conventional methods. The reported research results lays the groundwork for developing simplified models for other types of loading such as flexure.