Influence of prestressing on the punching strength of post-tensioned slabs

• 15 Test results are presented investigating the effects of prestressing on the punching shear strength.
• Contrary to available tests, the different effects of prestressing are investigated separately.
• The results are investigated on the basis of the physical model of the Critical Shear Crack Theory.
• The suitability of this theory for punching design of prestressed slabs is demonstrated.
• The evaluation of the physical parameters of this theory is adapted to the case of prestressed slabs.

Previous researches on punching of post-tensioned slabs have shown a number of phenomena significantly influencing their strength and behaviour. However, no general agreement is yet found on a physical theory (either in codes of practice or in design models) suitably describing the influence of prestressing and how should it be accounted on the punching shear behaviour. In this paper, the authors present the results of tests on 15 slabs (3000 × 3000 × 250 mm) tested to failure under different loading conditions. The aim of the tests was to investigate in a separate manner the different actions induced by prestressing on the punching shear strength (in-plane forces, bending moments and bonded tendons). These results are finally investigated on the basis of the physical model of the Critical Shear Crack Theory. The fundamentals of this theory are presented and adapted to post-tensioned slabs, providing a rational explanation of the observed phenomena and measured strengths.