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WALL FOOTINGS

Wall footings consist of concrete strips placed under walls. The most common type of wall footing consists of a strip with a rectangular cross section projecting an equal distance as a cantilever from both faces of the wall. For soil stress the critical dimension of the footing is the width of the footing bottom measured perpendicular to the wall face.

In most situations the wall footing is used as a platform upon which the wall is constructed. Thus a minimum width for the footing is determined by the wall thickness, the footing usually being made wider than the wall. With a concrete wall this additional width is used in order to support the wall forms while the concrete is poured. For masonry walls this added width assures an adequate base for the mortar bed for the first layer of the masonry units.

With relatively lightly loaded walls the minimum width required for platform depends on the allowable bearing stress on the soil. In this case, the short projection of the footing from the wall face will produce relatively transverse bending and shear stresses, permitting a minimum thickness for the footing and no transverse reinforcing. Most designers prefer, however, to provide some continuous reinforcing in the long direction of the footing, even when none is used in the transverse direction.

As the wall load increases the increased width of the footing required for the control of soil stress eventually produces significant transverse bending and shear in the footing. At some point this determines the required thickness for the footing and for required reinforcing in the transverse direction.

When the building has no basement and the floor consists of a concrete slab placed directly on the ground, these footings are sometimes poured monolithically with the floor slab.

Notes:

bearing stress напряжение смятия

mortar bed растворная постель

projection n. выступ

1. What do wall footings consist of?

2. What is the most common type of wall footing?

3. How is the critical dimension of the footing calculated?

4. Is wall footing used as a platform?

5. What is a minimum width for the footing?

6. When is the additional width for the footing used?

7. What does the minimum width required for platform depend on?

8. What will the short projection of the footing from the wall face produce?

9. Where do most designers prefer to provide reinforcement of the footing?

10. When are footings poured monolithically with the floor slab?

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