Define the contact rectangle
Keep length along x and width along y consistent with the diagram and the applied moments.
CRANE & SITE / TOOL 23
Rectangular Foundation Pressure Calculator
Explore the linear full-contact pressure distribution beneath a rigid rectangular base under compression and two moments.
Before you start: required inputs
- Use the base drawing for its contact dimensions and coordinate directions.
- Obtain the vertical force and both moments reduced to the centre of the same base contact plane for one load case.
Calculation diagram
A PRACTICAL WALKTHROUGH
How to use this calculator
Apply centre-based actions
Use compression for N and the signed moments about the x and y axes.
Check the model status first
If a trial corner pressure is negative, the no-tension full-contact assumption no longer represents the actual contact area.
4 m × 3 m rigid base
THE INPUTS
4 m length, 3 m width, 1,200 kN compression, 150 kN·m about x and 200 kN·m about y.
THE RESULT
Mean pressure is 100 kPa. The four trial corner values are 150, 100, 100 and 50 kPa, so all remain non-negative for this entered case.
What does the result mean?
01
Non-negative corners establish the assumed full-contact pressure condition only.
02
Negative trial pressure indicates tension in the linear solution; a no-tension bearing surface needs partial-contact analysis instead.
03
Pressure values must still be assessed against the relevant soil, footing, anchor and settlement requirements.
Watch for this
Taking moments at the column top and applying them at the footing base without transferring the forces and lever arms.
Formula & model conditions +
q(x,y) = N/(L B) + M_x y/I_x + M_y x/I_y
I_x = L B³/12; I_y = B L³/12
q_corners = N/(L B) ± 6M_x/(L B²) ± 6M_y/(B L²)
- Rigid base and linear pressure distribution over the entire rectangular contact area.
- Moments and vertical force must all refer to the base centre. Positive compression is used.
- A negative calculated corner pressure invalidates the full-contact model for a no-tension bearing surface. Partial contact, anchors, settlement and soil bearing resistance require another model.
Common questions
Can I use the negative corner number as soil tension?
No. For a no-tension soil interface it is a trial-model warning, not an actual tensile soil pressure.
Does a non-negative result verify the foundation?
It does not check soil bearing resistance, settlement, concrete strength, reinforcement, sliding or anchors.