. The elements of railroad engineering . the detail at The stress 23 000upon each rod is, therefore, — = 11,500 lb. With a factor of safety of G, the breaking stress would be 11,500 XG = G9,000 lb. We accordingly look in Table 53 for thediameter of a rod with a breaking stress of 69,000 lb., andfind it to be Ijg- in. To insure ample safety, we increasethe diameter to 1^ in. The pull placed upon the rods r, rplaces the needle-beam// under compression to an amountequal to u y, which, by the given scale, amounts to 21,500 find by reference to Art. 1809, that for endwisecrushing stress w
. The elements of railroad engineering . the detail at The stress 23 000upon each rod is, therefore, — = 11,500 lb. With a factor of safety of G, the breaking stress would be 11,500 XG = G9,000 lb. We accordingly look in Table 53 for thediameter of a rod with a breaking stress of 69,000 lb., andfind it to be Ijg- in. To insure ample safety, we increasethe diameter to 1^ in. The pull placed upon the rods r, rplaces the needle-beam// under compression to an amountequal to u y, which, by the given scale, amounts to 21,500 find by reference to Art. 1809, that for endwisecrushing stress we may use a working stress of 3,000 lb. persq. in. Hence, to resist this stress of 21,500 lb., we must add to the area of the needle-beam ^V^—— = sq. in., 3,000 ^ nearly. To hold the strut q in place, ribs cast with the strutfit into notches cut into the under side of the notches, as well as those cut in the side of the needle-beam for the straining rods, somewhat reduce the area of 12G8 RAILROAD RAILROAD STRUCTUREvS. 12G9 its cross-section, and to insure ample strength we increasethe depth of the needle-beam to 12 in. The straining rods are fitted at both ends with nuts andheavy cast washers which cover the entire end of the needle-beam, as shown in the cross-section (T, and in detail at are cast on the backs of the washers, which fit intogrooves cut into the ends of the needle-beam. The floor system is so arranged that the street cars shalluse only one side of the bridge, leaving the other side ex-clusively for vehicles. The rails are laid directly overstringers, which are proportioned to carry cars loaded totheir utmost capacity. A fully loaded street car weighs 10 tons. This is carriedon a wheel base (the horizontal distance between the cen-ters of wheels) of G ft. G in. Say this is equivalent to acenter load of 7 tons, or 3^ tons on each stringer. Thedepth of these stringers will, of course, be the same as thatof the floor-b
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
