Basics in Building Construction

Basics in Building Construction 4(2+2)

Lesson 02 : Shallow Foundations

Combined Footings

A spread footing which supports two or more columns is termed as combined footing. The combined footing may be of the following kinds:

Combined footings are invariably constructed of reinforced concrete.

1. Rectangular Combined Footing
   The combined footing for column will be rectangular in shape if they carry equal loads. The design of rigid rectangular combined footing should be done in such a way that centre of gravity of column loads coincide with the centroid of the footing area.

1. Trapezoidal footing
   If the columns carry unequal loads, the footing is of trapezoidal shape. When the columns carry equal loads, rectangular combined footings can be provided and when the columns carry unequal loads trapezoidal combined footings may be provided.

1. Combined column-wall footing
   The design of combined rectangular and trapezoid combined footing is shown in figure 11 below. Sometimes, it may be required to provide a combined footing for columns and a wall. In suchcases combined column-wall footing is provided.