Combined Footing Design
Substructure considers combined footings to act as a continuous beam in the global X-direction. For combined spread footings, a uniform bearing pressure taken as the maximum bearing pressure from four corners, is applied on the bottom of the footing. For a combined pile cap, the concentrated loads taken as the maximum pile reaction are applied at each pile location. The location of the columns is considered fixed. The moment and shear are calculated at the critical sections, using the model described above.
The combined footing is assumed to act as a cantilever in global Z-direction. The same bearing pressure or concentrated forces as those calculated in the X-direction are used, and all other calculations are computed in the same way.
The following figure shows a structural model used for the design of a combined footing in the global X-direction.
A structural model for the design of a combined footing in the global Z-direction is below.
