Pad footing which comes into the class of shallow footings is one of the simplest of all foundations. Pad footings are used on firm foundations to transfer column loads to the soil. They usually come as one pad footing for one column as shown below.
Under certain circumstances, two column loads are necessary to be carried by one pad footing which in this case is known as combined pad footing. The circumstances include:
1. Where the adjacent columns are too close that required pad footings overlap each other (see Figure below).
2. When a column is close to the boundary of the site that a separate foundation will be eccentrically loaded, the foundation of the adjacent column are linked to the column to overcome uplift, overturning or opposing forces. Here, trapezoidal or rectangular footing may be used which depends on the position of the more heavily loaded column (see Figures below).
3. Where a frame building is to be erected alongside an existing structure, it is often necessary to use a cantilever or asymmetrically combined base for column next to the existing building so that pressure on the soil due to the base may not so heavily surcharge the subsoil under the foundation of existing building so as to cause appreciable settlement.