Design of a reinforced-concrete highway bridge . ji _ /â47,400 - 5 3/4. Therefore a d of 6 is grea Fl^ â 12x121enough. The total shear at the outside edge of the girder equals675* 1,600 * 270 * 110 - 2,655 lbs. The Unit shear equals 2,655 - 37 lbs. per sq. in. 12x6 This is so small that the slab will need no reinforcement for shearAssuming that the allowable bond stress is 80 lbs. per sq. in. , abar must theoretically be imbedded in the concrete a length of 50diameters - 50 x 5/8 - 31 1/4 inches. However, since there isnegative moment over the girders an additional length of bar forbond will b
Design of a reinforced-concrete highway bridge . ji _ /â47,400 - 5 3/4. Therefore a d of 6 is grea Fl^ â 12x121enough. The total shear at the outside edge of the girder equals675* 1,600 * 270 * 110 - 2,655 lbs. The Unit shear equals 2,655 - 37 lbs. per sq. in. 12x6 This is so small that the slab will need no reinforcement for shearAssuming that the allowable bond stress is 80 lbs. per sq. in. , abar must theoretically be imbedded in the concrete a length of 50diameters - 50 x 5/8 - 31 1/4 inches. However, since there isnegative moment over the girders an additional length of bar forbond will be required; the bars will therefore extend across thewidth of the bridge. 47. Design of portion of floor slat) between Girders. The equivalent uniform live load for a fifteen ton engineis assumed by many designers to be 300 lbs. per so. ft., and thisvalue will be used. Fig. 18 shows diagramatically the loadings. /=7^. /S Loadtnqs far F7oor Stab BetweenGirders. 300* Live Load /Jot *T5*Earth _i 1 a, I 60aF/.SIat> Considered \ /10*rI. Slab. Let R equal the reaction at the center of the to the loading shown in Fig. IB. Then E = 675 +2 x 135 * x 465 B - 675 + 270+ 1627 - 2,572Since the slab is symetrically load/the max. moment in the slabbetween the girders occurs at the center line of the bridge. X = ( + - 675 x ^6 - 270 x 7 - 465 x x )12 II - ( + 12,250 - 5,840 - 1,890 - 2,850)12 = 1,670 x 12 LI - 20 ,00Q# d = 9 - 1 1/2 = 7 1/2 b = 12 16000 f s bd 20 ,000,, - *, f Q = 300 p - p H = -002 x 12 x = per bars spaced 9 on centers give an area of # per the above design is correct, but practicallyit is wrong for the following reason. It is a well known fact thatwhen fresh concrete is poured upon a concrete surface, even the thelatter has already set, there will be more or less adhesion betweenthe freshly poured concrete and the older concrete when the formerbegins to harden. There will theref
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