Experimental and analytical investigation of punching shear capacity of biaxial voided slabs

Biaxial voided slab is an emerging slab system which reduces its self-weight up to 50% in comparison with the conventional reinforced concrete solid slab. The reduction in the concrete volume does not affect its flexural capacity significantly, however, it reduces both one-way and two-way (punching)shear capacity about 40%. Therefore, an effective way of predicting the punching shear capacity is investigated as the presence of voids alters the critical failure section. The applicability of conventional methods for solid slabs in the design standards, such as ACI 318 (2014), EN 1992-1-1 (2004)and IS 456 (2000)to predict the punching shear capacity of the voided slab is examined. In addition, eight full-scale specimens were tested with the sphere and cuboid shape of voids. Finally, experimental results of present study and test data collected from literature (33 specimens)were compared with predictions by the relevant code provisions. The estimation of punching shear capacity of biaxial voided slab by existing provisions for solid slabs in standards does not lead to satisfactory results. Hence, the presence of voids is considered by modifying the critical section depending on the void location. Further, only the effective concrete area is considered to predict the punching shear capacity. After the modifications, the predictions by all three building standards lead to satisfactory results.