Vertical Progressive Collapse of Cmposite Floor Systems under a Side Column Removal Scenario: Experimental and Numerical Investigations

The propensity of buildings for progressive collapse can be assessed using the alternative path method. Generally, there are three scenarios to be considered: internal column, side column, and corner column removals. Many researchers have conducted robustness analysis of two- and three-dimensional substructures subjected to internal column removal, but only limited studies have investigated side and corner column removals. Because the side and corner columns are exposed directly to the external environment, they are more susceptible to damage caused by extreme events occurring outside the building. This paper presents experimental and numerical investigations of progressive collapse behavior of a 1:3-scale six-column subframe composite floor system subjected to the removal of a side column. A specially designed six-point loading system was adopted to apply an equivalent uniform load to the composite floor slab. The load was applied in a displacement-controlled manner to trace the complete load-displacement behavior at the point of column removal. The experiments also captured the stress distributions, failure patterns and load-transferring mechanisms. A reduced nonlinear finite-element (FE) model was developed to capture the load-displacement behavior of the tested frames, and the predicted results were compared with those from the tests. It was found that the collapse of the composite frame system is governed by the failure of primary beam-column connection. The resistance to progressive collapse is contributed predominantly by the flexural action (FA). Contradicting observations by other researchers, enhanced resistance due to catenary action (CA) in the beam and tensile membrane action (TMA) in the slab were not observed in the tests. In addition, the dynamic increase factor (DIF) obtained from the energy balance method was found to be in reasonable agreement with the factors proposed by Department of Defense recommendations.