Module 11
Foundations and pile caps
Where structural design meets the ground — and where the two most consequential mistakes are both about which limit state you are working in.
What this module covers
- Separate the geotechnical sizing from the structural design, and use the right loads for each
- Size a pad footing from an allowable bearing pressure
- Check bearing pressure under combined axial load and moment, including uplift
- Design a pad for bending, beam shear and punching shear
- Explain why a pile cap is designed by strut and tie, not by bending
- Recognise when minimum reinforcement governs, which in footings is often
Lessons
- 11.1
Pad footings
Two calculations on the same base, at two different limit states, with two different sets of loads.
Start lesson → When the base lifts off at one edge, and when the member is too deep for bending theory to apply at all.
Start lesson →
Module checkpoint
Check what you have taken in
6 questions
Question 1
Why does the base's own weight not appear in the structural design of a pad footing?
Question 2
A column carries 1600 kN characteristic. The allowable pressure is 175 kPa and the base is 700 mm thick. What square side is required, in m?
Question 3
A 2.5 m square base carries a factored load of 1500 kN from a 350 mm square column. What is the ultimate bearing pressure, in kPa?
Question 4
For that base, what is the design moment at the column face, in kNm?
Question 5
A bearing-pressure calculation returns a minimum pressure of −40 kPa. What does this mean?
Question 6
Two piles at 2000 mm centres carry a factored column load of 2800 kN through a cap with d = 750 mm. What is the tie force, in kN?