Punching shear capacity of lightweight aggregate concrete flat slabs without shear reinforcements

This study examined the effect of the unit weight and compressive strength of concrete on the punching shear capacity of flat slabs without shear reinforcements. The slabs were prepared using all-lightweight aggregate concrete (ALWAC), sand-lightweight aggregate concrete (SLWAC) and normal-weight concrete (NWC) at the different compressive strengths of concrete of 24 and 45 MPa. Based on the upper-bound theorem of concrete plasticity, the failure surface generatrix is generalised to account for the increased horizontal extension with a decrease in the unit weight of concrete. Thus, the punching shear capacity of concrete flat slabs is mathematically driven considering the reduced effective strengths of lightweight aggregate concrete under tension and compression. Test results showed that the radius of the punching shear tended to increase with a decrease in the unit weight of concrete. This yielded a lower normalised punching shear capacity observed for ALWAC and SLWAC flat slabs than NWC flat slabs. The proposed model accurately estimated the punching shear capacity, indicating that the mean and standard deviation of the ratios between the experiments and predictions were 1.10 and 0.05, respectively. This indicated that the proposed model reasonably reflects the reduced aggregate interlock action of lightweight aggregates.