How do you calculate the soil bearing pressures?
For design and construction simplicity, generally the combined footings are designed as rectangular when the loads of the two columns are about of the same order of magnitude. However there are cases where one column load is much larger than the other, and therefore this desired simplification is not economically feasible. In those cases the footing should be designed as trapezoidal, so that the resulting bearing pressures are about uniform. Another example of a trapezoidal footing is when the available space is limited due to the presence of other existing footings in the area.
The calculation of the bearing pressures is relatively simple for rectangular footings in full bearing, but it becomes increasingly complex for trapezoidal footings. Furthermore, the calculation is very cumbersome when the footing is in partial bearing. ASDIP FOUNDATION uses an algorithm consisting of double integrals of the type P = ∫∫z dy dx where z is the bearing stress. The centroid of the bearing area is therefore Ẍ = ∫∫x z dy dx / P. Evidently, this complexity arises due to the variable nature of the trapezoidal footing geometry and the uncertainty of the location of the zero pressure line.
ASDIP FOUNDATION accurately calculates the soil bearing pressure distribution for a rectangular or trapezoidal combined footing in either full or partial bearing, as shown in the picture below.