Suppose we are designing a footing for the wall of a building. There are two checks that are crucial.
- Ground support: suppose the ground is assessed as being suitable to load up to 80 kN/m2. Then a wall that places a line load of 40 kN/m on the footing, needs a footing 500mm wide at minimum.
- Eccentricity: Suppose in the above example, the footing is closed to one side than the other. Then the pressure on one side could still be more than ground support can be relied upon, even if the footing is over 500mm wide. The pressure at both edges must be under 80 kN/m2, not just the average pressure under that value.
But there are a further 2 possible factors to consider.
- Footing's self-weight: The footing itself could have significant mass, and will usually be denser than the supporting subsoil, shouldn't it be included in the overall load? and
- Stabilising effect of footing itself: its own considerable mass will tend to stabilise it (by adding a substantial additional moment to the eccentricity check and therefore, although it increases total ground pressure, it also reduces ground support pressure difference across the footing), and reduce overall eccentricity.
Do we take those into effect? I've never seen it done on an ordinary house wall or similar scale structure, so is it wrong to do so, or just insignificant, or a problem?
Note: UK construction norms being considered if that matters