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Measurement of Masonry

tons, feet, pile, load, weight and inches

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MEASUREMENT OF MASONRY There are no universally adopted rules for measuring stone masonry, and the custom in the openings for windows and doors as solid, thus adding to the actual number of cubic feet in the wall. Another rule sometimes adopted is to take out the openings, and add a cubic foot for each linear foot of corners to be finished, in cluding the vertical sides of the windows and doors.

For example, let Fig. 15 represent the plan and elevation of the front of a small building to be measured. According to the first rule, the volume is: (8+25)x 12x cubic feet. By the second rule, it is: 594— (4 + 18+ 48) X x 6+32=593 cu. ft.

If the extras for the corners be counted 18 inches thick, the result will be 52 cubic feet more, or 645 cubic feet.

If the corners are in foundations under ground, they are usually left so rough that no allowance is made for building them.

Usually openings not wider than twice the thickness of the wall are measured as solid; and some allowance is agreed upon as extra to be added for building corners, curves, or other un usual work.

It is seen from the above example, that as much as ten per cent of the total volume may depend upon the method adopted in the meas urement. Accordingly, care should be taken that all parties concerned are, from the first, ac quainted with the practice to be adopted.

The weight on the soil is 2,150 tons—or 1.8 tons per square foot, average pressure. The effect of the wind is thought to be such as to make the maximum pressure 2.4 tons. There are in stances in Boston, Mass., where soft clay car ries from tons to 4 tons safely. The building laws of the given locality must always be con sulted before designing foundations for any building.

Improving the Bearing Power of Soil.

When ever the required load exceeds those given above, means must be taken to improve the character ter of the soil, or to provide other support. The bearing power of even soft material is much im proved by enclosing it with a row of short piles to prevent lateral movement and to make pos sible the dr4inage of the enclosed area. If the

site be above an outlet for the water, drainage may be provided by means of tile around the outside. This is also an effective way of im proving the foundation bed. Again, covering a wet, unstable, foundation bed with concrete or even with sand, to a depth of one or two feet, has a marked effect upon its bearing power. "Smeaton mentions a stone bridge built upon a natural bed of gravel only about 2 feet thick, overlying deep mud so soft that an iron bar 40 feet long sank to the head by its own weight."* Foundations on Piles. In many cases it is cheaper to drive piles to secure a suitable bear ing than to remove the soft material overlying a proper foundation bed. The safe load that a pile will support has been the subject of some ex periments and much speculation; but no unfail ing rule has been deduced. The expression de signed to show this load that is in most common use is known as the Engineering News formula: in which P is the safe load on the pile, and W is the weight of the hammer of the pile-driver, both being taken in the same unit, usually tons; h is the height in feet through which the hammer falls; and s is the penetration in inches of the pile under the last blow. That is, the safe load in tons on a pile is equal to twice the weight of the hammer in tons multiplied by the fall in feet and divided by 1 plus the penetration of the pile in inches under the last blow.

For example, if a hammer weighing 2,000 pounds, falling 20 feet, causes the pile to sink• 1.5 inches under the last blow, then the safe load, by the formula, will be : A pile under similar actual conditions is said to have been loaded with 7.5 tons, with the re sult of causing much settlement. Another pile, driven with the same weight and fall, sank 26 inches under the last blow, but carried 7.5 tons safely. The piles under the coal pockets on Lin coln wharf, Boston, Mass., are said to carry 12 tons each, safely; and loads of 40 tons are being carried on single piles elsewhere.

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