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.

A preliminary analysis and discussion of the condominium building collapse in surfside, Florida, US, June 24, 2021

“…The reinforcement layout of the column strip is shown in 9. Previous studies [9][10][11][12][13][14][15] reveal that the mechanical performance of the slab-column joint after punching shear failure is mainly dominated by the through-column integrity rebars. The following two typical characteristics can be summarized from the reinforcement layout of the collapsed structure: 1) the flexural reinforcement at the slab top is trimmed at a certain distance away from the column faces; 2) half amount of the integrity reinforcement at the slab bottom is cut off at the slabcolumn joint region, and the remaining half is overlapped within the column region, in which the overlap length of the rebars is only 149 mm.…”

“…Note that different design codes set distinctively different requirements for the reinforcement detailing of the joints [7,8]. The performance difference of various kinds of detailing can only be compared through experiments or refined FE analyses [9][10][11][12][13][14][15][16]. Experimentally, the punching shear and post-punching failure behaviors of a series of interior slab-column joints subjected to either concentric loading or eccentric loading were investigated, considering the effects of different punching shear directions, slab thicknesses, reinforcement ratios, and strengthening methods [10,14,15].…”

“…It was found that the post-punching bearing and deformation capacities of the slab-column joints were predominantly determined by the through-column integrity reinforcement, and the addition of the embedded beams facilitated greater deformation and load capacities in the large-deformation suspension stage. Xue et al [9] and Ma et al [12,13] conducted a series of tests of flat plate substructures subjected to either concentrated load on the column stub or uniformly distributed load on the slab. The load redistribution patterns of these substructures were examined and accurately quantified under different column removal scenarios.…”

Simulation of punching and post-punching shear behaviours of RC slab–column connections

“…Test results of eight 1/3-scaled SCC specimens (Fig. 1) (Yang et al, 2018;Diao et al, 2018;Diao et al, 2019) were used to develop and calibrate the proposed numerical model. The punching and post-punching shear behaviours of these specimens, considering different punching shear directions (denoted as "DPS" and "UPS"), slab thicknesses and reinforcement 6 ratios were investigated.…”

“…Regarding post-punching shear behaviour, limited experiments were conducted to investigate the post-punching shear capacity (Melo and Regan, 1998;Diao et al, 2019) and the influencing design variables such as slab thickness, amount and arrangement of integrity bars, and inclusion of shear reinforcement (Habibi et al, 2012;Ruiz et al, 2013). Along with these experimental investigations, several analytical studies have also been conducted.…”