Concrete Pavement Truck Equivalence Factors For Upgrades
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Presented in this paper are the upgrade truck equivalence factors for single unit trucks of type, 1.2 and 1.22 which are not covered by AASHTO. The equivalency factors for front and rear axles of single unit trucks were developed using AASHO Road Test equation after considering the decrease in front axle load and the increase in rear axle load due to the axle load redistribution on upgrades. The axle loads on upgrades are function of position of center of gravity of the truck, wheel base, upgrade magnitude and truck weight. The truck equivalence factors are obtained by summing up the equivalency factors of front and the corresponding rear axles. For upgrade truck equivalence factors the new term H / B representing the ratio of the height of the center of gravity H to the base length of single unit truck is of great importance. The upgrade truck equivalence factors were developed taking into consideration the following three values for upgrade namely; 0%, 8% and 12%, four values of slab thickness namely; 6, 8, 10 and 12 inches (15.24, 20.32, 25.40 and 30.48cm) and two extreme ratios of H / B of 0.2 and 1.0. Three values for terminal levels of serviceability of 2, 2.5 and 3 were considered. The paper reveals that the upgrade truck equivalence factors increase as the upgrade slopes as well as slabs thickness increase. The increase in the equivalence factors is of significance at the higher values of H / B than at the lower ones.