. Railway age . e rib will l>e reinforced with steel. Let K, = ,000 lbs. per square Inch, and iC. = 30,000,000 lb*. D. L. + L. L. 108,300 n. r,. + L. L. = 82,700 lb€.-ft.—28,200 140,000 Xi — 140,000+ ft. yt — , __— — — •f 65,0001411,000 In like manner each set of loadings Is considered. Any otherHeld can be taken by simply adding the values of H,, M,, V„ etc.,in Tabli; A corresponding to the loading used. alent to 20 square Inches of concrete. Let 1 per cent, of the area at the crown be assumed as ste«l,or of a square foot of equivalent concrete, and place the ce
. Railway age . e rib will l>e reinforced with steel. Let K, = ,000 lbs. per square Inch, and iC. = 30,000,000 lb*. D. L. + L. L. 108,300 n. r,. + L. L. = 82,700 lb€.-ft.—28,200 140,000 Xi — 140,000+ ft. yt — , __— — — •f 65,0001411,000 In like manner each set of loadings Is considered. Any otherHeld can be taken by simply adding the values of H,, M,, V„ etc.,in Tabli; A corresponding to the loading used. alent to 20 square Inches of concrete. Let 1 per cent, of the area at the crown be assumed as ste«l,or of a square foot of equivalent concrete, and place the centerof the steel ft. from the outside of the concrete. The effectlrearea is now + = sq. ft. = F at the crown, and practicallyat section number 10. I ^ the moment of Inertia := and the section modulusS = Since the values of .^ must always remain In the relative mag-nitudes shown in column 2 of Table A, If the moment of inertia is o OOOO o o o o Cori^e for e/p - ft/g. Fig. 4. In Table C are given the values of H„ M,, etc., for the variousloadings considered. Since the first four sets are symmetrical, onlyont>-half of each equilibrium polygon is drawn, as shown In Fig. the Inst two sets the loading Is not symmetrical and hence thepolygons must bo constructed for the entire span. Proceed as fol-lows: Lay off y, and y, at the left support and y^ at the crownand construit both halves of the polygon on the left of the crownas shown in Fig. 3. All of Iho above results arc obtained with comparatively littlelabor and in a short time. As usually considered the arch rib, asshown In Fig. 1. would be passed as quite safe for the given load-ings. Hut tht> effect of the axial thrust and temperature changesremain lo bo considered. The olToit of the axial thrust will be lirst taken up. The hori-zontal thrust is Increased at any section, the moment of inertia at each other sec-tion must be Increased In like proportion. At the crown the
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