When work is done on some materials systems, their internal geometric states are altered in such a way that they have the potential to "give back" work when the force is removed and the system returns to its original configuration. This stored energy is called strain energy. Strain energy density (strain energy per unit volume) is a function of the Young's modulus of elasticity and Poisson's ratio and the nine strain (or stress) components; but it is independent of the coordinate system. Material properties are input into the Chevron N-layer computer program to calculate the strain components.

Having calculated the strain energy density at a point, another quantity called "work strain" can be defined as the value of the strain corresponding to an uniaxial stress situation leading to the same strain energy density at the point. It can be used as the ''effective" strain and is related to any single component of strain. Thus, pavement design systems based upon a single component of strain may be easily converted to a strain energy density basis.

Configurations with loads distributed equally between the axles of an axle group were evaluated and damage factor relationships are reviewed. However, inspections of tandem axle suspensions on semitrailer trucks have shown that most tandem groups do not distribute the load equally to the axles. A theoretical investigation was made using pavement structures identical to those tested at the AASHO Road Test. The 1976 W-6 Table for Kentucky was used to obtain actual weight data. Preliminary analyses of tandem groups for 3S2 vehicles revealed a 40-percent increase in EAL over that calculated EAL assuming the total load on each tandem group had been uniformly distributed to the axles.

Report Date


Report Number

No. 537

Digital Object Identifier



1980 Annual Meeting The Association of Asphalt Paving Technologists (Louisville, Kentucky).