Some notes on the Fourier transform application in veroad with respect to the permanent deformation

In pavement design of asphalt roads, the occuring strains and stresses are calculatedwith the aid of a linear multi layer computer program. In the past only a version for an elastic material was available. Because the material behavior of asphalt is more visco-elastic than elastic, a new program is developed using Burger's model for the description of the visco-elastic response of asphalt.The solution procedure in VEROAD is based on a Fourier transform. The problems with the Fourier tranform are solved by using the calculated Fourier transform to determine the vertical shift and calculate the correct answer. The VEROAD program is used for the calculation of permanent road deformation. Because in practice the permanent deformation development of asphalt, as measured in creep tests, will not be linear in time, two models are develloped for an estimate of the actual permanent deformation in an asphalt layer, using a combination of VEROAD and the repeated (dynamic) creep test. This document gives the calculations and the two models.