Types of Foundations

A wide variety of concrete foundations are used for buildings. Some of the most common types are illustrated in Fig. 9.41.
Spread wall footings consist of a plain or reinforced slab wider than the wall, extending the length of the wall (Fig. 9.41a). Plain- or reinforced-concrete individual- concrete spread footings consist of simple, stepped, or sloped two-way concrete slabs, square or rectangular in plan (Fig. 9.41b to d). For two columns close together, or an exterior column close to the property line so that individual spread or pile-cap footings cannot be placed concentrically, a reinforced-concrete, spreadcombined footing (Fig. 9.41e) or a strap footing (Fig.. 9.41Æ’) can be used to obtain a nearly uniform distribution of soil pressure or pile loads. The strap footing becomes more economical than a combined footing when the spacing between the columns becomes larger, causing large bending moments in the combined footing.
For small soil pressures or where loads are heavy relative to the soil capacity, a reinforced-concrete mat, or raft foundation (Fig. 9.41g) may prove economical.
A mat consists of a two-way slab under the entire structure. Concrete cross walls or inverted beams can be utilized with a mat to obtain greater stiffness and economy.
Where sufficient soil strength is available only at lower levels, pile foundations (Fig. 9.41h) or drilled-pier foundations (Fig. 9.41i) can be used.

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  1. sakthi Thiru

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