Punching shear of slabs: crack size and size effects

Fictitious crack model assumptions and equilibrium equations were used to develop a numerical model in order to predict the punching load and the deformations of reinforced concrete slabs. Concrete strength, aggregate type, reinforcement ratio as well as the fracture strength properties were taken into account in developing the new model. In spite of the low tensile strength of concrete, it has considerable fracture energy, therefore the fracture process zone in front of a growing crack can contribute to the flexural concrete strength. The proposed model adopted the fictitious crack model principles. The three equilibrium equations were used on a radial segment of the slab and the effect of crack size and size effect were incorporated in the formulation. The model results were compared with the experimental results and currently available shear design formulae to investigate the effect of the fracture properties on the predicted punching load. The model provided consistent and improved results compared to the existing codes.