This paper documents the findings from a dynamic collapse experiment carried out on a single-story two-by-two bay reinforced concrete flat-plate substructure. The test specimen had a 0.4 scale, represented older flat-plate buildings designed without structural integrity reinforcement in slabs, and was subjected to an instantaneous removal of an exterior supporting column. Tests were conducted three times with different levels of gravity load until a progressive collapse occurred. The specimen survived a gravity load corresponding to 42% of the normal loading capacity defined by the direct design methods but collapsed at a load of 49% of the design loading capacity. The collapse of the specimen was initiated by the punching failure at an interior slab-column connection carrying the most redistributed load after the exterior column removal. The tests confirmed the existence of slab compressive membrane action and examined the strain rates of material under dynamic response. The tests also indicated that a slab-column connection without continuous slab bottom reinforcement through the column has limited post-punching resistance. The experiment indicated that an older flat-plate building is vulnerable to a progressive collapse when it is subjected to a sudden exterior column removal. Numerical simulations of the experiments using a macromodel were conducted and its effectiveness was confirmed.

Reinforced concrete (RC) flat-plate structures are vulnerable to punching shear failure at their slab-column connections, potentially leading to a catastrophic progressive collapse. In practice, the slab-column connection above an interior column, removed due to abnormal loads, may be subjected to a concentrated downward force because of the absence of the supporting column and further being pushed as a result of different live load intensities on individual stories. This force is different from the full design load that the column withstands in normal situations and, combined with the gravity load acting on the slab, may cause punching shear failure at the interior slab-column connection. This will further trigger failure propagation to the surrounding slab-column connections. This paper presents the experimental tests performed on two identical large-scale $2\times 2$ -bay RC flat-plate specimens under an interior column removal scenario. A 5-kPa uniformly distributed load was applied first to the slab followed by an incremental concentrated force imposed on the slab-column connection above the removed interior column. The complete collapse-resistant behavior and load redistribution pattern of the specimens were investigated and are reported herein. Results show that more than 90% of the applied concentrated force is solely distributed to the four nearest adjacent columns. Three load-carrying mechanism phases, in the form of flexural, tensile membrane, and a combination of one-way catenary and dowel actions can be distinguished in resisting the applied concentrated load.