71. Example

A 4-foot footing course of limestone transmits a load of 12 tons per lineal foot or 3 tons per square foot; the thickness of the course is 10 inches. What should be the width of the course above ?

Answer. - From the table under the column headed 3 we find the projection to be 1.1 times the thickness, or in this case 11 inches. As we would have the same projection each side of the wall, the stone above may be 22 inches less in width, or 2 feet 2 inches wide. Except in cases where it is necessary to obtain very wide footings it is better not to make the offsets more than 6 or 8 inches, and in the case above it would be better to make the upper footing course 3 feet wide. Most building ordinances require the projection of the footings beyond the foundation wall to be at least 6 inches on each side.

71 Example 10032

Fig. 31.

71 Example 10033

Fig. 3a.

71 Example 10034

Fig. 33.

71 Example 10035

Fig. 34.

72. Brick Footings

On sandy soils brick foundations and footings may be used when good stone cannot be cheaply obtained. In Denver, Col., where the soil is a mixture of sand and clay, very dry and unaffected by frost, brick foundations have been found to answer the purpose fully as well as stone for two and three-story buildings.

In building brick footings, the principal point to be attended to is to keep the back joints as far as possible from the face of the work, and in ordinary cases the best plan is to lay the footings in single courses; the outside of the work being laid all headers, and no course projecting more than one-quarter brick beyond the one above it, except in the case of unloaded 9-inch walls. The bottom course should in all cases be a double one. Figs. 31-34 show the proper arrangement of the brick in walls from one to three bricks in thickness. If the ground is soft and compressible, or the wall heavily loaded, the footings should be made wider, as shown in Fig. 35. For brick footings under high walls, or walls that are very heavily loaded, each projecting course should be made double, the heading course above and the stretching course below.

The bricks used for footings should be the hardest and soundest that can be obtained, and should be laid in cement or hydraulic lime mortar, either grouted or thoroughly slushed up, so that every joint shall be entirely filled with mortar. The writer favors grouting brick walls, that is, using thin mortar for filling the inside joints, as he has always found it to give very satisfactory results.

The bottom course of the footing should always be laid in a bed of mortar spread on the bottom of the trench, after the latter has been carefully leveled. All bricks laid in warm or dry weather should be thoroughly wet before laying, for, if laid dry, the bricks will rob the mortar of a large percentage of the moisture it contains, greatly weakening the adhesion and strength of the mortar.

Too much care cannot be bestowed upon the footing courses of any building, as upon them depends much of the stability of the work. If the bottom courses are not solidly bedded, if any seams or vacuities are left in the beds of the masonry, or if the materials themselves are unsound, the effects of such carelessness are sure to show themselves sooner or later, and almost always when they cannot be well remedied. Nothing is more apt to injure the reputation of a young architect than to have a building constructed under his direction settle and crack, and he should see personally that no part of the foundation work is in any way slighted.

72 Brick Footings 10036

Fig. 35.