Post-punching mechanisms of slab–column joints under upward and downward punching actions

Abstract

Progressive collapse of reinforced concrete flat plate systems can be significantly influenced by the post-punching performance of their slab–column joints under large deformations. This work presents a series of static collapse tests on four flat slab–column joint specimens with slab in-plane restraint. The effects of different punching directions (upward and downward) and embedded beams on the post-punching performance of the joints were studied. The test results reveal that the post-punching load-bearing and deformation capacities are mainly governed by the longitudinal through-column reinforcement in the slab. The peak bearing capacities and failure modes of specimens without embedded beams were significantly influenced by different punching directions. Conversely, the post-punching mechanisms of specimens with embedded beams were identical regardless of their opposite punching shear actions. In addition, the inclusion of the embedded beams increased the resistance capacity of the specimens under both flexural and suspension mechanisms and enhanced the deformation capacity under the suspension mechanism. Furthermore, a finite-element numerical model was developed and verified against the test results. Based on the numerical study, the contributions of the concrete and reinforcement in resisting the collapse of the slab–column joints were evaluated.