SHALLOW FOUNDATION - Combined Footings: Rectagular, Trapezoidal and Column-Wall Footings.

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

(i) Rectangular combined footing [Fig. 2.5 (a)]
(ii) Trapezoidal combined footing [Fig 15(b)]
(iii) Combined column-wall footings [Fig. 25(a),(b)]

Combined footings are invanably construcied of reinforced concrete.

FIG 2.5  COMBINED FOOTINGS FOR COLUMNS.

The combined footing for columns 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 columu loads coincide with the centroid of the footing area. If the columns carry unequal loads, the footing is of trapezoidal shape, as shown in Fig. 25 (b).
Sometimes, it may be required to provide a combined footings for columns and a wall. Such combined footings are shown in Fig  2.6 (a) [when the columns carry equal loads] and in Fig. 2.6 (b) [when the columns carry unequal loads].

FIG. 2.6 COMBINED FOOTINGS FOR COLUMNS AND WALL