Influence of the Distribution and Level of Post-Tensioning Force on the Punching Shear of Flat Slabs

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.