Basic concept of punching failure

Punching failure is a type of structural fracture that occurs mainly in reinforced or prestressed concrete slabs when a concentrated load or point support generates high shear stresses around the contact zone. This situation causes the slab to fracture in a shear manner around the perimeter of the support, perforating or 'punching' the slab, which can lead to a sudden collapse without significant prior deformations.

This phenomenon is especially critical in elements such as foundation slabs, lightweight slabs and solid slabs that support pillars or columns. The importance of studying punching failure lies in its dangerous and low-ductile nature, which implies the need for careful design to guarantee structural safety and avoid catastrophic failures.

Origins of shear stress in slabs

The shear stress generated by punching appears when concentrated loads, such as the weight of a pillar or a machine, are transmitted through the slab. These loads induce high shear stresses in the contact zone, which if they exceed the resistant capacity of the concrete and the reinforcement, cause a cone-shaped crack around the support.

The slab geometry, thickness, stiffness and the possibility of load redistribution affect the magnitude of these shear stresses. Furthermore, the presence of transverse reinforcement or perimeter reinforcement can significantly modify the punching behavior.

Factors contributing to failure

Among the factors that increase the probability of failure due to punching are the low thickness of the slab, the high concentration of load in a small area, insufficient shear reinforcement and the lack of perimeter reinforcement. The quality of the concrete, the presence of discontinuities and the support conditions also influence.