Stress in the Footing Bottom
The stress in the footing bottom can be assumed as:
- rectangular (uniform in the footing bottom)
- general (trapezoidal) with different edge values
The general distribution of stress follows from the figure:
Stress in the footing bottom
where:
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where: | Q | - | vertical load of footing |
l,b | - | footing width and length | |
eb | - | load eccentricity | |
M | - | moment acting on the footing | |
H | - | horizontal force | |
N | - | normal force at the eccentric footing | |
p | - | column axis offset from the footing center |
If in some points the stress becomes negative, the program continues with adjusted dimensions b*l while excluding tension from the analysis. Before computing the stress distribution due to surcharge the stress in the footing bottom is reduced by the geostatic stress in the following way:
There are three options in the program to specify the geostatic stress in the footing bottom:
- From the original ground It is therefore considered, whether the footing bottom in the open pit measured from the original ground is free of stress for the time less than needed for soil bulking and subsequent loss of stress in the subsoil.
- From the finished grade The same assumptions as above apply.
- Not considered at all.