. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools . ybe noticed that, assuming a uniform load per running foot, boththe pressure per square inch at the ends of the stringers (the 174 RAILROAD CONSTRUCTION. § 144. caps having a width of 12) and also the stress due to trans-verse strain are kept approximately constant for the variablegross load on these varying spans. Clear span. No. of piecesunder each rail. Width. Depth. 10 feet12 ♦•14 ** 223 8 inches 10 ♦• 10 ** 16 inches16 16 ** 144. Corbels. A corbel (in trestle-work) is a sti
. Railroad construction. Theory and practice. A textbook for the use of students in colleges and technical schools . ybe noticed that, assuming a uniform load per running foot, boththe pressure per square inch at the ends of the stringers (the 174 RAILROAD CONSTRUCTION. § 144. caps having a width of 12) and also the stress due to trans-verse strain are kept approximately constant for the variablegross load on these varying spans. Clear span. No. of piecesunder each rail. Width. Depth. 10 feet12 ♦•14 ** 223 8 inches 10 ♦• 10 ** 16 inches16 16 ** 144. Corbels. A corbel (in trestle-work) is a stick of timber(perhaps two placed side by side), about 3 to 6 long, placedunderneath and along the stringers and resting on the are strong prejudices for and against their use, and acorresponding diversity in practice. They are bolted to thestringers and thus stiffen the joint. They certainly reduce theobjectionable crushing of the fibers at each end of the stringer,but if the corbel is no wider than the stringers, as is generallythe case, the area of pressure between the corbels and the cap is. Fig. 80. no greater and the pressure per square inch on the cap is no lessthan the pressure on the cap if no corbels were used. If thecorbels and cap are made of hard wood, as is recommended bysome, the danger of crushing is lessened, but the extra cost andthe frequent scarcity of hard wood, and also the extra cost andlabor of using corbels, may often neutralize the advantagesobtained by their use. 145. Guard-rails. These are frequently made of 5X8 stuff,notched 1 for each tie. The sizes vary up to 8X8, and thedepth of notch from J to IJ. They are generally bolted toevery third or fourth tie. It is frequently specified that theyshall be made of oak, white pine, or yellow pine. The jointsare made over a tie, by halving each piece, as illustrated in The joints on opposite sides of the trestle should be stag- § 146. TRESTLES, 175 gered. Some roads fasten every tie
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