What is Punching Shear?

What is punching shear?

✓The weight of a slab supported on a column induces shear stresses in the slab.

✓ These stresses, if sufficient and where additional reinforcement is not provided, would result in the column ‘punching’ through the slab.

✓Punching shear failures arise from the formation of diagonal tension cracks around the loaded area, which result in a conical failure surface as illustrated in Fig.

Punching Shear Design

The design to prevent punching shear failure proceeds as:

1. Check if the concrete is strong enough alone;

2. If not, check if the amount of reinforcement is reasonable;

3. Design reinforcement if reasonable, if not, change form of structure.

✓Changing the form of structure includes deepening the slab, making the column larger, introducing drop panels or flared column heads.