. Handbook of railroad construction; for the use of American engineers. Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States .. . rm is applicable to spans under twentyfeet. The proper dimensions are found by the formula — I A:W L ^=V 50001 =^^^^P^^- Example, — The depth of a beam of twenty feet span,and twelve inches wide, to support a load of twenty thou-sand two hundred and fifty lbs. is -v/- 4X20250X20X12 ,„ . , 5000 X 12 = ^^ ^^^- A beam 12 X 18, and of 20 feet span, will therefore bearsaf
. Handbook of railroad construction; for the use of American engineers. Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States .. . rm is applicable to spans under twentyfeet. The proper dimensions are found by the formula — I A:W L ^=V 50001 =^^^^P^^- Example, — The depth of a beam of twenty feet span,and twelve inches wide, to support a load of twenty thou-sand two hundred and fifty lbs. is -v/- 4X20250X20X12 ,„ . , 5000 X 12 = ^^ ^^^- A beam 12 X 18, and of 20 feet span, will therefore bearsafely a load of 20,250 lbs., applied at the centre. In this manner is formed the following table, giving thescantling of sticks for railroad stringer bridges, of twentyfeet span and under. Span. Breadtu. Depth. 5 12 12 10 12 13 12 12 15 15 12 18 18 12 20 20 12 21 inches. The first scantlings exceed the requirement of the rule, butare none too large to resist the shocks to which such sticksare exposed. Cross-ties of plank, 2 or 3 by 6 or 8 inches, and plankbraces underneath, (as shown in the fig. at the end of chap-ter VIII.,) should be bolted to the main timbers; the same 140 HANDBOOK OF RAILROAD CONSTRUCTION. Fig. bolt passing through the tie beam and plank. The longi-tudinal pieces should be firmly notched and bolted to thewall-plates, and these latter either built in or scribed on tothe masonry. 172. For a span of from 20 to 50 feet, we may use thecombination shown in fig. 61. The piece A B, must be so strong as not toyield between Aand D, or D andB. The piecesC E, must be stiffenough to resistthe load comingupon them whichis as follows. A locomotive engine of the heaviest class willnot exceed fifty tons weight, each pair of driving wheels willsupport ten tons, and on each side five tons, 2240 X 5,11,200lbs.; or to allow for shocks and extra strains, 15,000 brace, then, must support seven thousand five hundredpounds, which for compression simply would requ
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