Eight bars will be placed parallel to the edge of the footing and eight on the diagonal in each direction; they may cover a greater width than the base of the pier, and will be spaced 5 inches apart, thus making each hand 3 feet wide and covering the whole area in a satisfactory manner.
The method for diagonal tension in a slab of this form has not been satisfactorily worked out. If we apply the method proposed by Professor Talbot for slabs with flat-top surface, we have, on a section distant 2S inches from the base of the pier, and no diagonal tension reinforcement is necessary. As the section to resist diagonal tension is increased by the slope of the top surface of the beam, it seems reasonable to employ the 'method in this instance.
Various modifications of these forms of footing are often employed, depending upon the same principles in design, but varied to suit special needs or to secure greater economy in the use of materials. Ribs may sometimes be used to advantage in distributing the loads upon the slab.
Cantilever Foundations.—When it is necessary to carry the side walls or wall columns of buildings upon footings which cannot pro ject beyond the face of the wall on the outside, cantilever footings are often employed, wherein the wall columns rest upon one arm of a cantilever beam, the of her arm of which carries an interior column, the cantilever being so proportioned as to center the total load upon the footing which supports it. Footings of this type are often neces sary when the loads upon the wall columns are greater than those upon the interior column, so that the ordinary combined footing is not applicable. The designs for such footings vary widely accord ing to the requirement of the particular foundation and the ingenuity of the designer. Usually the adjustment of dimensions upon such footings is made for cleacl load only, or by using such part of the live loads as may reasonably be supposed to be ordinarily upon the foun dation.