Concrete Pavement Truck Equivalence Factors For Upgrades
Abstract
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.