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 due to the absence of the supporting column and further being pushed due to different live load intensities on individual stories. This force is different to the full design load that the column withstands in normal situation and, combined to the gravity load acting on the slab, may cause punching shear failure at the interior slabcolumn 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 2×2-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 form of flexural, tensile membrane, and a combination of one-way catenary and dowel actions can be distinguished in resisting the applied concentrated load.
Reinforced concrete (RC) flat plate structures are broadly used in car parks, residential and office buildings due to their economic and architectural advantages. However, this structural system is inherently prone to punching shear failure, which may propagate horizontally and vertically, ultimately leading to the progressive collapse of the entire structure or of a large portion of it. This paper presents the experimental results from two quasi-static largedisplacement tests performed on a 1/3 scale, 2×2-bay, RC flat plate substructure subjected to corner column removal scenarios. The specimen was tested twice with different corner
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.
The punching and post-punching shear behaviours of reinforced concrete (RC) flat plate structures are often studied by using a representative slab–column connection isolated from the parent structure. In this study, a set of numerical modelling techniques is established to create a competent three-dimensional non-linear model to simulate punching and post-punching shear behaviours of RC slab–column connections without shear reinforcement, through the use of which the punching shear failure featuring a critical punching shear surface and an abrupt drop of the applied force in the load–displacement response is able to be accurately reproduced. The post-punching shear behaviour, taking the form of an increased load-carrying capacity which is ceased by rebar fracture in the suspension stage, is also well captured. Using the proposed numerical model, typical punching and post-punching shear failure mechanisms are studied in some detail.
To investigate the influence of critical parameters on the progressive collapse resistance of reinforced concrete (RC) flat plates, a set of finite element modelling techniques was established. Especially, the modelling of bond-slip behaviour between concrete and rebars was highlighted, which was found to have a significant impact on the performance of flat plates.Employing the modelling strategy, our previously tested 2 2-bay flat plate substructure (S-1) and a similar specimen (ND) in the literature were simulated for model validation. Key structural behaviours, including tensile membrane and suspension actions in the large deformation stage, could be accurately replicated. Further, the validated S-1 model was used to conduct a series of parametric studies in which the influence of concrete strength, slab thickness and reinforcement ratio on the collapse performance was examined. The results indicated that the concrete strength and the slab thickness only affected the slab flexural ManuscriptClick here to access/download;Manuscript;Manuscript_Revised.docx capacity with no impact on the load-carrying capacity after the initial flexural/shear failure.Moreover, the load-carrying capacity due to tensile membrane action was primarily governed by the reinforcement ratio. Further examination on the lateral stiffness suggested a lower bound ultimate flexural strength enhancement of 17%, due to the compressive membrane action, can be obtained.
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