Applications of the critical shear crack theory to punching of R/C slabs with transverse reinforcement

The traditional approach of codes of practice for estimating the punching strength of shear-reinforced flat slabs is based on the assumption that concrete carries a fraction of the applied load at ultimate while the rest of the load is carried by the shear reinforcement. Concrete contribution is usually estimated as a fraction of the punching strength of members without shear reinforcement. The ratio between the concrete contribution for members with and without shear reinforcement is usually assumed constant, independent of the amount of shear reinforcement, flexural reinforcement ratio, and bond conditions of the shear reinforcement. The limitations of such an approach are discussed in this paper and a new theoretical model, based on the critical shear crack theory, is presented to investigate the strength and ductility of shear-reinforced slabs. The proposed approach is based on a physical model and overcomes most limitations of current codes of practice. Its application to various punching shear reinforcement systems is also detailed in the paper and its results are compared to available test data.