Pile Cap Design
Punching and one-way shear on a pile cap. The cap is deep and heavily loaded, so punching around the column and beam shear across the pile line are the two checks that size it.
| Depth (mm) | Punching utilisation |
|---|---|
| 600 | 78% |
| 700 | 61% |
| 800 | 49% |
| 900 | 41% |
| 1000 | 34% |
vu = Vu/(bo·d) · bo at d/2 from the column.
φvc = 0.75 × 0.33√f'c · ACI 318 §22.6.
A clear path from inputs to results.
Punching and one-way shear on a pile cap. The cap is deep and heavily loaded, so punching around the column and beam shear across the pile line are the two checks that size it.
How to use
- Set column load (kn).
- Set column size (mm).
- Set effective depth (mm).
- Set concrete f'c (mpa).
- Read the headline metrics, then check the table for the detail.
The formula
Reference: ACI 318 §22.6 punching at d/2 from the column face.
Worked example
At the default inputs
- Column load (kN): 3000; Column size (mm): 500; Effective depth (mm): 800; Concrete f'c (MPa): 35; Piles: 4
- 1
Punching stress: 0.72 MPa · Concrete capacity: 1.46 MPa · Utilisation: 49% · Piles: 4
Punching stress: 0.72 MPa · Concrete capacity: 1.46 MPa · Utilisation: 49%
Interpreting the result
A 3000 kN column on a 800 mm cap gives 0.72 MPa against 1.46 MPa.
Assumptions & limitations
- Rigid cap, uniform pile reaction.
- No shear reinforcement.
Frequently asked questions
Why does depth help so much?
The perimeter grows with d and the stress falls with d — twice.
When is shear reinforcement needed?
When the utilisation exceeds 100%, or the cap becomes very deep.
Methodology last reviewed 2026-10-22. Results are informational and not financial or engineering advice — see our disclaimer.