Experimental study of beam–slab substructures subjected to a penultimate-internal column loss

• Penultimate-internal column loss is a critical scenario.
• Behavior of beam–slab structures under the scenario is experimentally observed.
• Catenary and T-beam effects on load capacity of the structures are evaluated.
• Possible collapse modes of associated building structures are identified.

Progressive collapse resistance of reinforced concrete building structures can be evaluated by using column loss scenarios. The loss of a penultimate column is among the most critical scenarios since it leave the associated structures with the least lateral restraint. At large deformations, any mobilization of catenary action, as an alternative load path, should rely solely on the strength of a perimeter compressive ring forming within the deflected slabs. This paper presents an experimental study to investigate the static response of double-span beam–slab substructures bridging over a penultimate-internal (PI) column. Three ¼ scaled beam–slab substructures were designed, built and tested by a static loading scheme. The boundary condition of specimens was rotationally and vertically restrained, but laterally unrestrained. A 12-point loading system was used to simulate uniformly distributed loads. The static response of the test structures was identified with negative bending moments that were greatly affected by T-beam effect, and catenary action replacing positive bending moment in the central region at very early stage. At large deformations, the overall load-carrying capacity of test structures although benefit from the continuous development of catenary action, was adversely affected by accompanying partial failures such as fracture of beam bottom bars and compressive failure of beam-to-column connections. Based on failure modes of test structures, the typical collapse mode of actual buildings was further discussed.