Punching Shear Strength of Restrained Slabs

The punching shear strength of restrained concrete slabs is investigated. A rational idealized model of a restrained slab at punching failure is developed. This model is an extension of one previously developed by Kinnunen and Nylander for simply supported slabs. The influence of boundary restraints on punching load is demonstrated and the model is shown to yield accurate estimates of the punching strength of slabs with known boundary restraints. An empirical factor, termed the restraint factor, is introduced to estimate the influence of boundary restraints and can be used in the design of slabs for which the actual restraints are not exactly known. The restraint factors for a number of restrained slab systems are reported.