Punching Shear
Definition
A failure mode in which a concentrated load punches through a concrete slab around its bearing perimeter. It can occur at a column-slab connection, a lifting collar, or any concentrated bearing on a flat slab.
- Domain
- Structural forensic engineering
- Mechanism
- Concentrated load punches through a slab at the bearing perimeter
- Common sites
- Column-slab connections, lifting collars, concentrated bearings
Common questions
How is punching shear failure recognised at a collapse scene?+
Investigators look for a cone-shaped or truncated-pyramid fracture surface around the column or bearing point, which is distinct from the broader radiating crack patterns typical of flexural slab failure.
Why are flat-slab structures particularly vulnerable to it?+
Flat slabs have no beams to distribute load around columns, so shear stress concentrates directly at the column-slab interface, making reinforcement detailing at that connection critical to preventing a brittle punching failure.
Related terms
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- Column Tributary Area
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- Disproportionate Collapse
- Collapse extent that is far greater than would be expected from the triggering event. Ronan Point is the canonical example: a small...
- Lift-Slab Construction
- A method in which floor slabs are cast at ground level and hydraulically jacked up steel columns to their final position. The...
- Post-Tensioned Slab
- A concrete slab in which steel tendons running through plastic ducts are tensioned after the concrete hardens, improving span capacity. Corrosion of...