SAFE LOADS AND BREAKING LOADS. The following table gives the safe working loads allowable in good practice for brickwork, masonry, and foundation soils; in other words, calculations may be based directly on the values given, without using any factor of safety. Rubble, laid in lime mortar. Rubble, laid in cement mortar Concrete, 1 Portland, 2 sand, 5 broken stone Foundation Soils. 80 150 150 Tons per Sq. Ft. BREAKING LOADS FOR ROUND CAST-IRON COLUMNS. (In Thousand Pounds.) Length of Column in Feet. 8 ft. 10 ft. 12 ft. 14 ft. 16 ft. 18 ft. 20 ft. 418 505 412 1,830 1,580 1,460 1,292 1,143 1,010 895 12 12 13 13 13 13 14 14 14 14 2,030 1,810 1,470 1,310 1,160 MATERIALS OF CONSTRUCTION. STONE. Granite is the most valuable stone where strength is required, its crushing strength averaging about 20,000 lb. per sq. in. Exposed to fire, it disintegrates at a temperature of from 900° to 1,000° F., being less durable in this respect than fine-grained, compact sandstones. The average weight oi granite is about 167 lb. per cu. ft. Limestone is a very common building stone, and, when compact, is very durable. It is usually quite absorptive, and becomes dirty quickly; while under intense heat, it is converted into lime. Limestone must be well seasoned before use, to get rid of the quarry water. The strength of limestone varies from 7,000 to 25,000 lb. per sq. in., the average being about 15,000 lb. The weight of limestone is about 155 to 160 lb. per cu. ft. Sandstone is, in general, an excellent building stone, capable of resisting great heat, and the better kinds absorb only small quantities of water. The dark-brown, flinty sand. stones retain their color very well, ranking better than granite. A stone containing much pyrites becomes unevenly discolored, due to formation of rust, and, hence, the stone should be carefully examined in this respect. The average strength of sandstones is about 11,000 lb. per sq. in., varying from 4,000 to 17,000 lb. The weight of sandstone is about 140 ib. per cu. ft. When a good stone is tapped with a hammer, it gives out a ringing sound. The absorptive quality of a stone may be tested by noting the increase in weight after soaking in water for 24 hours. One that increases 5 per cent. or more should not be used. BRICK. If two good bricks are struck together, they give out a ringing sound; while if the sound is dull, the brick is of inferior quality. A good brick will not absorb more than 10 per cent. of its weight of water; the best will not absorb over 5 per cent., while soft brick will take up from 25 to 35 per cent Solid terra cotta weighs about 120 lb. per cu. ft., while hollow pieces of ordinary size average from 65 to 85 lb. The safe working strength of terra-cotta blocks in walls is about 5 tons per sq. ft., if unfilled, and 10 tons, if filled solid with concrete LIME. Lime weighs about 66 lb. per bu., or about 53 lb. per cu, ft. One barrel of lime, weighing 230 lb., will make about 24 bbl., or .3 cu. yd., of stiff paste. In 1-to-3 mortar, 1 bbl. of unslaked lime will make about 64 bbl. of mortar; or 1 bbl. of lime paste will make about 3 bbl. of mortar. For a 1-to-2 mortar, about 1 bbl. of quicklime to 5 or 54 bbl. cf sand are used. CEMENTS. The two kinds of hydraulic cements are termed Portland and natural (often called Rosendale, from a place in New York where much of it is made). Portland cements are dark in color, weigh from 90 to 100 lb. per cu. ft., are very slow in setting, and attain great ultimate strength. Natural cements are light in color, weigh from 50 to 60 lb. per cu. ft., are very quick setting, and become from to as strong as Portland cement. |