For the uniformly distributed load maximum moment occurs at mid-span, therefore, IRC Class-70R tracked vehicle is placed symmetrically at mid-span to produce maximum moment. For the IRC Class-70R tracked vehicle, whose wheel contact length is large, but shorter than medium span bridges, the load is assumed uniformly distributed over the wheel contact area. Absolute maximum bending moment due to vehicular live load is usually calculated using the rolling concept. For the two-lane Indian highway bridges, IRC code recommends that the bridges should be designed Class-70R/Class-AA tracked and wheeled vehicles placed on one lane and the bridge need to be checked for Class-A loading on both the lanes. For the design of highway bridges, IRC code specifies two types of live loads namely Class-A and Class-70R/Class-AA. and it is considered uniformly distributed throughout the span. In the concrete bridges, a major portion of loads is due to dead loads which include self-weight of bridge superstructure, railing load, footpath, wearing course, water/electricity/telephone lines etc. For the elastic design of bridge, usually the design moment is obtained by superimposing the maximum moments due to dead load and live load effects. For the aseismic design of bridges for gravity loads, traditionally, dead load and live load in conjunction with impact load are considered for the design of the bridge superstructure. Finally, in order to enable the designers, the design moments due to Class-70R wheeled and Class-A loading have been presented in tabular form for the spans from 10 to 50 m.ĭesign of bridges for flexure requires determination of maximum bending moment in the deck. The aim of the present study is to find the number of wheels for Class-A and Class-70R wheeled vehicles and their precise location to produce absolute maximum moment in the bridge considering the effect of dead loads and impact factor. Moreover, in case of Class-A and Class-70R wheeled vehicular live loads, which consists of several axels, the number of axels to be considered over the bridge of given span and their location is tedious to find out and needs several trials. Since, the location of absolute maximum bending moment due to multi-axel vehicle do not coincide with the location of maximum moment due to dead loads occurring at mid-span, the design moment may not be obtained by simply superimposing the effect of dead load and live load. For the simply supported bridges, uniformly distributed dead load produces maximum moment at mid-span while the absolute maximum bending moment due to multi-axel vehicles occur under a wheel which usually do not lie at mid-span. Usually, the design moments in the simply supported bridges are obtained as the sum of moments due to dead loads and live load where the live load moments are calculated using the rolling load concept neglecting the effect of dead loads.
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