Prediction of Punching Shear Capacity of Biaxial Voided Slab

Radha Sagadevan, BN Rao


Biaxial voided slab systems are advantageous due to their reduced self-weight, up to 50 % in comparison with the conventional reinforced concrete solid slab. The reduction in the concrete cross sectional area reduces the shear capacity up to about 40 %. The prediction of punching shear capacity in voided slab is not direct unlike in solid slab. This is because the presence of voids alters the critical failure section and hence the punching load. In the present study, the applicability of conventional method (adopted for solid slabs) in the Indian design standard IS 456: 2000 is explored for predicting the punching shear capacity of the voided slab. In addition, three full-scale specimens were tested with sphere shaped voids. Finally, experimental results of present study and test data collected from literature (23 specimens) are compared with theoretical predictions. The estimation of punching shear capacity of biaxial voided slab by existing provisions for solid slabs in IS 456 do not lead to satisfactory results. Hence, the presence of voids is considered by adopting an effective concrete area available to resist punching shear at the critical section. It is found that the estimated capacity based on IS 456 with effective concrete area is in good agreement with experimentally observed capacity.


Reinforced concrete slab, voided slab, punching shear, two-way shear, effective concrete area


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