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.(shown in image above)
✓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:
- Check if the concrete is strong enough alone;
- If not, check if the amount of reinforcement is reasonable;
- 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.
CIVILIANS 