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Punching capacity is one of the main items in the design of both pre-stressed and non-pre-stressed flat slabs. All international design codes include provisions to prevent this type of failure. Unfortunately, there is no code provision for UHPC yet, and hence, the aim of this research is to experimentally investigate the impact of column dimensions and punching reinforcement on the punching capacity of post-tensioned slabs and compare the results with the international design codes’ provisions to evaluate its validity. The test program included five slabs with a compressive strength of 120 MPa: one as a control sample, two to study the effect of column size, and the last two to study the effect of punching reinforcement. Comparing the results with the design codes showed that ACI-318 is more accurate with an average deviation of about 5%, while EC2 is more conservative with an average deviation of about 20%. Besides that, punching reinforcement reduces the size of the punching wedge by increasing the crack angle to 28° instead of 22° for slabs without punching reinforcement. Also, the results assure that both ductility and stiffness are enhanced with the increased column dimensions and punching reinforcement ratio. Doi: 10.28991/CEJ-2023-09-03-06 Full Text: PDF

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Punching shear is the most common failure mechanism of slabs that are supported directly on columns. The slab–column connection is always vulnerable to critical punching shear; thus, it is necessary to investigate the effect of various parameters on the punching shear behavior of the flat slabs. This work presents an experimental study to evaluate the effect of the level of prestressing force and layout of the strands on the punching shear behavior of the slab–column connection in terms of the maximum load, deflection, stiffness, ductility, and the absorbed energy. Five square post-tension flat slabs (2000 mm × 2000 mm) with 150 mm thickness were tested. Increasing the prestressing force increased the maximum load and the ductility with a delay in damage in the case of uniformly distributed strands. Additionally, the banded layout of the post-tensioning strands significantly increased the punching shear capacity of the post-tensioned flat slabs at all levels of prestressing. The influence of the layout of the strands on the flat slab ductility is clearly visible in cases of high prestressing force as the ductility decreases in cases with distributed strands when compared to the same flat slabs with banded strands. Finally, the predicted values of the ultimate load of the punching shear using different codes, including the Egyptian Code of Practice (ECP-203), the American Building code (ACI-318), the CEB-FIP Model code and the Euro code, are compared to the experimental values of the ultimate punching shear strength of the post-tensioned and non-post-tensioned flat slabs.