It is found that a heavy pier will sink proportionally more than a light one, so that the area under the larger piers is made relatively greater than under the smaller ones.

Again, it is necessary to take into account the material of which the superstructure is to be built. Thus, a footing under a brick wall is made larger than a footing under a line of iron columns, so that if both footings are loaded with the same weight, that under the columns will settle the most, to allow for the compression in the joints of the mason-work.

It is impossible to build heavy buildings on the Chicago soil without settlement, and the architect must therefore plan his building so that all parts shall settle equally, and this has, been successfully done in many of the largest buildings.

In a building where the footings are proportioned to give a bearing weight on the ground of 2 tons per square foot, it is estimated that the building will settle about 4 inches altogether.

Piling has been successfully used under several buildings in Chicago, and there seems to be no reason why it should not be more extensively resorted to.

In the construction of the large grain elevators which are scattered through the city the loads are so excessive, reaching as high as six tons per foot, that it would be impracticable to support them on ordinary footings, and piling has been resorted to. The piles are driven a distance of twenty to forty feet down to hard-pan, capped by wooden sleepers, with heavy wooden cross-beams and solid planking to receive the masonry.

CONCRETE FOOTING FOR FOUNDATIONS.

For the footings of foundations in nearly all kinds of soil where piles are not used, the writer believes a good concrete to be preferable to even the best dimension stone, for the reason that it acts as one piece of masonry and not as individual blocks of stone, and if made of sufficient thickness it will possess sufficient transverse strength to span any weak place in the soil beneath, if not of large

area.

When the best brands of Portland cement are used, the proportions may be as follows:

One part Portland cement; 3 parts clean sharp sand; 5 parts chip stone, in sizes not exceeding 2 × 1 × 3 inches. Using these proportions, one barrel of cement will make from 22 to 26 cubic feet of concrete.

The above proportions were used in the concrete for the foundations of the Mutual Life Insurance Company's Building, New York City

When the cement is not of the best quality, or other cement than Portland cement is used, more cement should be used with the other material. Using a cement made in the West, the author specifies that one part of cement to two of sand and four of broken stone should be used, and the result has been very satisfactory.

It will generally be found wise to keep an inspector constantly on the ground while the concrete is being put in, as the temptation to the contractor to economize on the cement is very great.

In mixing the concrete, the stone, sand, and cement should be thrown into the mortar box in the order named, and while one man turns on the water two or more men should rapidly and thoroughly work the material back and forth with shovels, when it should be immediately carried to the trenches. The concrete should be deposited in layers not over six inches thick, and each layer well rammed. If one layer dries before the next is deposited it should be well wet on top, just before depositing the next layer.

Care should be exercised to see that the trenches are not dug wider than the desired width of the footings; and also in mixing the concrete, not to use more water than is necessary to bring the mass to a pudding-like consistency, as otherwise the cement may be washed away.

COST OF CONCRETE.

The cost of labor in mixing concrete, when the proper facilities are provided, need not exceed three cents a cubic foot, and four cents is a liberal allowance, with wages at two dollars a day. The amount of materials required to make 100 cubic feet of concrete may be taken as follows: proportion of 1 to 6, 5 bbls. cement (original package) and 4.4 yards of stone and sand; proportion of 1 to 8, 3.9 bbls. of cement and 4 yards of aggregates.

The cost of concrete at the present time in Denver is about thirty cents per cubic foot.

The weight of concrete varies from 130 to 140 lbs. per cubic foot, according to the material used, granite aggregates making naturally the heaviest concrete.

CHAPTER III.

MASONRY WALLS.

Footing Courses.—In commencing the foundation walls of a building, it is customary to spread the bottom courses of the masonry considerably beyond the face of the wall, whatever be the character of the foundation bed, unless, perhaps, it be a solid rock bed, in which case the spreading of the walls would be useless. These spread courses are technically known as "footing courses." They answer two important purposes:

:

1st, By distributing the weight of the structure over a larger area of bearing-surface, the liability to vertical settlement from the compression of the ground is greatly diminished.

2d, By increasing the area of the base of the wall, they add to its stability, and form a protection against the danger of the work being thrown out of "plumb" by any forces that may act against it.

Footings, to have any useful effect, must be securely bonded into the body of the work, and have sufficient strength to resist the violent cross-strains to which they are exposed.

Footings of Stone Foundations. As, the lower any stone is placed in a building, the greater the weight it has to support and the risk arising from any defects in the laying and dressing of the stone, the footing courses should be of strong stone laid on bed, with the upper and lower faces dressed true. By laying on bed is meant laying the stone the same way that it lay before quarrying.

In laying the footing courses, no back joints should be allowed beyond the face of the upper work, except where the footings are in double courses; and every stone should bond into the body of the work several inches at least. Unless this is attended to, the footings will not receive the weight of the superstructure, and will be useless, as is shown in Fig. 1.

In proportion to the weight of the superstructure, the projection of each footing course beyond the one above it must be reduced, or the cross-strain thrown on the projecting portion of the masonry will rend it from top to bottom, as shown in Fig. 2.

In building large masses of work, such as the abutments of

bridges and the like, the proportionate increase of bearing-surface obtained by the footings is very slight, and there is generally great risk of the latter being broken off by the settlement of the body

of the work, as in Fig. 2. It is therefore usual in these cases to give very little projection to the footing courses, and to bring up the work with a battering-face, or with a succession of very slight offsets, as in Fig. 3.

Footings of undressed rubble built in common mortar should never be used for buildings of any importance, as the compression of the mortar is sure to cause movements in the superstructure. If rubble must be used, it should be laid with cement mortar, so that the whole will form a solid mass; in which case the size and shape of the stone are of little consequence.

In general, footing stones should be at least two by three feet on the bottom, and eight inches thick.

The Building Laws of the city of New York require that the footing under all foundation walls, and under all piers, columns, posts, or pillars resting on the earth, shall be of stone or concrete. Under a foundation wall the footing must be at least twelve inches wider nan the bottom width of the wall, and under piers, columns,