Enhancing Punching Strength and Deformation Capacity of Flat Slabs

Punching reinforcement systems have significantly developed in recent years as they allow enhancing the punching resistance of slab-column connections as well as their deformation capacity. These systems, with varying geometry and layout, normally consist of vertical or inclined shear reinforcement with both ends anchored on the compression and tension side of the slab. For very high levels of load, when even common punching reinforcement systems cannot safely ensure the transfer of loads, steel shear heads are usually embedded in the slab to enhance the resistance of the connection. Yet, shear heads might be expensive and difficult to place in construction sites. Following the principle of the dowel action of the compression reinforcement, this paper introduces a novel system to efficiently reinforce slabs against punching shear by using large-diameter double-headed studs acting as shear dowels. This system enhances the performance of shear-reinforced slabs with respect to conventional solutions and might be an efficient alternative to shear heads for a large number of practical situations. The system is validated by means of a specific experimental program including 11 axisymmetric punching tests on interior slab-column connections. The results demonstrate not only the increase of the punching strength but also the deformation capacity of the connection. It is also shown that the system can be consistently designed accounting for the doweling forces by making use of the theoretical frame of the Critical Shear Crack Theory (CSCT), allowing to understand the activation of the shear dowels on the basis of the deformation of the member.