Experimental Study on Progressive Collapse of 3D Steel Frames under Concentrated and Uniformly Distributed Loading Conditions

Abstract

Structures are expected to be robust enough to avoid widespread local failure caused by extreme loading events, so that the complete or disproportional collapse of buildings can be averted. In the last decades, numerous studies have been conducted regarding preventing the progressive collapse of structures. In the steel frame tests that have been conducted, two-dimensional (2D) systems have normally been adopted. In addition, in previous studies, a concentrated load applied on a removed column has commonly been substituted for the gravity load from the superstructure; in light of the frame tests conducted by the authors, this may have substantially understated the collapse resistance of steel frames. In this study, two large-scale two-bay by two-bay steel frames were tested under a central column removal scenario subjected to concentrated loading and 12-point loading conditions. Flush end-plate joints were used to bridge over the primary beams and columns, and the secondary beams were connected to surrounding columns and primary beams through double-angle cleat joints. Based on the tests, the load-displacement responses and failure modes of three-dimensional (3D) steel frames were obtained. The individual contributions of collapse-resisting mechanisms, including flexural and catenary action in the respective primary and secondary beams, are discussed in detail. In this way, the influence of 3D frame effects and loading methods on progressive collapse were identified.