. Live-load stresses in railway bridges, with formulas and tables. that when114 of loading has advanced upon the bridge, this condi-tion is approximately satisfied. For this position of loading Mi = 22261 M, = (M3--M2) = (2565 - 175) = 2390 <=(l) = 1iS(-«^«») = -«^» Therefore, Si = .00580(22261) - .0466(2390) = 16\This value of ^2 = 16* balances % D = — 14*, nearlyenough for practical purposes. Therefore, compute T forthis position of the live load. ^ = 3^ = -00203 Mo = H (22261) - 2565 = 11340T = .00203(11340) = 23 Impact factor = -rrrj = .725 Impact stress for T = .725 X 23 - 17^ Problem
. Live-load stresses in railway bridges, with formulas and tables. that when114 of loading has advanced upon the bridge, this condi-tion is approximately satisfied. For this position of loading Mi = 22261 M, = (M3--M2) = (2565 - 175) = 2390 <=(l) = 1iS(-«^«») = -«^» Therefore, Si = .00580(22261) - .0466(2390) = 16\This value of ^2 = 16* balances % D = — 14*, nearlyenough for practical purposes. Therefore, compute T forthis position of the live load. ^ = 3^ = -00203 Mo = H (22261) - 2565 = 11340T = .00203(11340) = 23 Impact factor = -rrrj = .725 Impact stress for T = .725 X 23 - 17^ Problem 2. Live-load Stresses in a Pratt Truss with Parallel Chords. The complete data for this problem are given in Formulas (21), (29), and (30) give the values of the LIVE-LOAD STKESSES 47 coefficients G and H, which are identical for several mem-bers of any Pratt truss with parallel chords. The proce-dure for finding the positions of the loading and maximumstresses is exactly as in Problem 1. It should be noted that Stress FG = Stress EF X HI = Secant =-51^= 4- Fig. 14. Mem. G H Wheel M4 Ml S CD 0400 0800 4@1 3564 600 95 EF 00667 0400 3 3 13520 287 79 FG 106 GH 00667 0400 2 4 6170 100 37 HI 50 JK 00894 0536 2 5 2i79 ioo 14 DE 00894 0536 3 2 21895 287 181 BC 272 AC = AD 00595 0357 4 1 33970 600 181 AF = BE 01190 0357 7 2 31375 2694 278 BG 01785 0357 12 3 34411 8385 314 The stresses in all of the chord members may be checkedby use of Table 8, and the stresses in the end post and webmembers may be checked by Table 9. The stress in CDagrees with the maximum pier reaction in Table 7. Table3 may be used to find the position of loading for maximumchord stresses, and Table 6 gives position of loading formaximum web stresses. ARTICLE VIII. THREE-HINGED ARCH. APPLICATION OF THE GENERAL METHODTO THE CALCULATION OE LIVE-LOAD STRESSES. JO The general formulas -r- = xCW and S = sCikf may-be used directly to find the position of loading and the Uo U, Us Un U, U
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