What are combined footings?
COMBINED FOOTINGS:
When a footing supports two or more columns in the same line, it is called a combined footing. The combined footing which supports two columns is relatively common. The choice of shape is decided by the difference in column loads as well as physical limitations. Trapezoidal footings are used only when rectangular footings are not possible.
The footing geometry is made such that the resultant of several columns passes through the centroid of the footing area. This enables the designer to assume uniform soil pressure distribution.