Punching Shear for Concrete Structures

What is Punching Shear?

Punching shear is a unique and often underestimated type of failure that can occur in reinforced concrete structures, particularly in slabs or flat plates. When a heavy load, like that of a building, is placed on a slab, it generates a concentrated force. This force creates a specific type of stress known as punching shear, which can build up around columns, ultimately leading to a less-than-graceful collapse.

This sudden failure mode manifests as a shear-like crack that unpredictably extends from the column through to the slab face. Such a brittle and abrupt failure emphasizes the critical need for proper design and analysis when dealing with reinforced concrete structures.

Designing Against Punching Shear

Designing reinforced concrete flat plates isn’t a walk in the park, especially considering the large bending moments and shear forces that gather around slab-column connections. To combat this, engineers need to consider both the demand value and the capacity value when calculating punching shear. It’s worth noting that the calculations differ significantly for interior, edge, and corner cases. The following calculation is based on the condition of zero moment transfer.