Progressive Collapse Analysis of Multistory Moment Frames with Varying Mechanisms

Abstract

Multistory frame structures are generally simplified as single-story substructures to study their progressive-collapse resistance. In this study, a single-story substructure was investigated, and its behavior was applied to multistory frame analyses. However, by omitting the effect of the Vierendeel mechanism, the present simplified model could not completely reflect the mechanical behaviors of the entire structure. Based on the double-span beam model, the collapse mechanisms of the single-story substructure was investigated and a resistance calculation method for the beam and catenary mechanisms was proposed. To analyze the effect of the Vierendeel mechanism on the overall behavior of multistory frames, a top-story substructure model was established for the middle-column removal scenario, and the entire failed span was selected for corner-column removal. The contribution index of the Vierendeel mechanism against the progressive collapse was introduced. Then, a two-dimensional (2D) steel frame with four spans and four stories was considered as an example to discuss the force redistribution after middle- and corner-column removal and to verify the validity of the mechanisms mentioned. Incorporating the models, the process of demolishing four columns of the Ohio Union building was simulated. The results showed that the simplified models were reasonable. The top and bottom stories of the multistory frame showed different anticollapse mechanisms, and the Vierendeel mechanism together with other mechanisms resisted the unbalanced load. Furthermore, it was determined that the Ohio Union building has reasonable resistance to progressive collapse.