![]() Ii) At support design moment = -62 -670 = -732 Kgm. I) At mid span, design moment = 31 + 670 = 701 Kgm. Span and support moment in the longitudinal direction per metre = 670 x 0.8 x 1.25 = 670 K.gm. Span and support moment in the transverse direction per metre = 2872 x 0.8 x 1.25 = 2872 K.gm. ![]() Taking mid span and support moment as 80 percent of the above as stated before and allowing for 25 percent In the example, Class 70-R tracked vehicle will govern the design. ![]() It has been advocated that due to continuity, the mid-span moments may be reduced by 20 percent and the same moment may be taken as the support (negative) moment also. and moment in the longer (longitudinal) direction per metre width = W (m 2 + µm 1 = W (m 2 + 0.15 m 1) K.gm. Moment in the shorter (transverse) direction per metre width = W (m 1 + µm 2) = W (m 1 + 0.15 m 2) Kgm. The values of the coefficients m 1 and m 2 are obtained from the curves when the values of U/B, V/L and K (= B/L Shorter Span/ Longer Span)are known. Having got the values of U and V, the ratio of U/B and V/L may be determined. It depends on many factors such as the span-width ratio, properties of the bridge deck and the position of the live loads on the girders. The distribution of the live loads, on the other hand, is not a simple one. In designing the girders, the dead load of deck slab, cross-beams, wearing course, wheel guard, railing, etc., may be equally distributed over the girders. Since the dead load of the deck is uniformly distributed over the whole area, the method outlined by “Rankine & Grashoff” may be adopted in finding out the dead load moments. when a gap is maintained between the deck slab and the crossbeam, the slab may be designed as one way slab. In two-way slab, the live load moments due to a concentrated or locally distributed load may be worked out by “Pigeaud’s Method” but when the deck slab is not made monolithic with the cross beam i.e. If no gap between the deck slab and the cross beams is maintained, the slab panel becomes a two-way slab continuous in both the direction.
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