The above calculations should be entered in a memorandum book, kept for the purpose, somewhat as follows:

Data For Footings

UNDER ONE FT. OF SIDE WALLS.

UNDER COLUMNS.

Cubic feet of brickwork,

108 @ 120

=

12,960

lbs.

Cubic feet of stonework,

28@ 150

=

4,200

Total weight of wall....................................................

17,160

lbs........................

Nothing

Floor area supported 8 '.............................................................................................

16 X 1

4

= 224'

Weight of floors per ' 75 lbs.

Weight of roof per ' 60 lbs.

Total for six floors and roof:

510 x 8

=

4,080............................

510X 224

=

114,240

Live load per  ' -

1st, 2d and 3d floors, 150 lbs.

3d, 4th and 5th floors, 100 lbs.

Total live load, 8 x 750

=

6,000....................................

750x224

=

168,000

50% of this =.................................

3,000.

.......................................................

84,000.

Total load....................................................

24,240

.............................................................

198,240

Assumed bearing load, 6,000 lbs.

Width of footings under wall, 4 ft.; under columns, 33 ' less 10%, or 5' 6" x 5' 6'.

The front and rear walls, if continuous, would not have to support any floor loads, and the footings should be reduced in proportion. The footings under the piers supporting the ends of the girders should also be separately computed.

28. In the case of light buildings it will often be found that the computed width of footings will be less than that required by the building ordinance, in which case it will of course be necessary to comply with the ordinances or building laws. As a rule, the footings under a foundation wall should be at least 12 inches wider than the thickness of the wall to give it stability. Even in light buildings the footings under the different portions of the buildings should be carefully proportioned, so that all will bring the same pressure per square foot on the ground. In cases where the width of the footing is regulated by the building law, the pressure per square foot under the footing should be computed, and the footings under all piers, etc., proportioned to this standard. In cases where a high tower adjoins a lower wall the footings under the two portions must be carefully proportioned to the weight on each, otherwise the wall may crack where it is bonded into the tower.

Example II. - To illustrate the manner in which the width of the footings should be proportioned when the pressure under the footingsis very light, we will take the case of a one-story stone church, having side walls 20 inches thick and 22 feet high above the footings, and a tower at the corner 60 feet high, the first 22 feet being 24 inches thick and the balance 20 inches thick. The roof is supposed to be supported by trusses and purlins, so that only the lower 6 feet of the roof rests on the side walls. The side walls also carry 6 feet of the floor; the tower has a flat roof 12 feet square.

The computations for the weights on the soil under the side walls and under the tower wall would be as follows:

UNDER SIDE WALLS.

Stonework, 22' x 20"= 36 2/3 cu.ft. at 150 lbs. percu.ft.,

5,500 lbs.

Weight of first floor,

130 lbs. x 6' =

780 "

Weight of roof below purlin, 40 lbs. x6'=

240 "

Total weight on soil......

6,520 "

UNDER TOWER WALL.

Stonework,

22' x 24"

=...

44 cu

. ft.

38'X22"

= ...

63 1/3

II

107 1/3x150

=............

16,100

lbs.

Weight of floor, 130 x 6

=..

780

II

Weight of roof, 40 x 6

=..

240

If

Total weight on soil..............

17,120

II

Width of footings, 3 ft.

Pressure per ' under footings, 2,173 lbs.

Width of footings under tower, 17,1202,173=7.8 ft.

In this case the width of the footings under the side wall should be determined by the question of stability, and should not be less than 3 feet. Then if the pressure under the tower were reduced to the same unit per square foot, the tower footings would need to be nearly 8 feet wide. On firm soils, however, such as sand, gravel, or compact clay, it would not be necessary to make the footings so wide as this, as the soil would probably not settle appreciably under a considerably greater pressure, so that if the footings of the tower were made 6 feet wide, there would probably be no danger of unequal settlement. Of course the greater the unit pressure on the soil the more exact must be the proportioning of the footings.