Keywords: object-oriented, pre-processing, post-processing, pavement, finite element analysis, wander distribution, rutting, surface profile, graphical user interface.

Pavement rutting, or permanent deformation, has been a long-time problem for hot-mix asphalt (HMA) pavements. Since an HMA pavement is a layered structure, rutting can originate from any layer, which is also called the failed layer. In order to rehabilitate a rutted pavement, knowledge of the failed layer is necessary to make rehabilitation decisions. Although this knowledge can be obtained through the trench operation, it is unsafe, costly, and time consuming. In 1995, Simpson, et al., found that the transverse surface profiles on rutted pavements could be used for identifying the failed layers [1]. Fang, et al., studied the pavement surface profiles using nonlinear finite element analysis (FEA) and developed a new failure criterion validated with data from in-service pavements [2]. FEA has been proven to be very effective in studying various pavement failure problems. With aid of both high- speed computers and commercial finite element (FE) software, more detailed finite element models could be used in analyses to provide more detailed information as well as to improve accuracy. However, modelling in detail of the load transferred from the vehicles to the pavement surface is still a challenging task due to the facts that the stresses across the tire-pavement contact area are non-uniform and that there also exists a transverse wheel wander distribution. Roadside statistical data show that this wander distribution can be approximated quite well with a normal distribution function [3], and experimental data of detailed contact stresses distribution within the contact area of commonly used tires are available at different load levels [4]. Even so, manually converting the dynamic load with multiple stress levels into quasi-static load with different magnitudes and durations, though possible, are time-consuming and error-prone. In practice, manually generating these data is not feasible because a single change in any one of the following parameters, loading time, magnitudes of contact stresses, distribution of contact stresses, wander distance, transverse position of axel centre, and tire configurations, will forfeit the existing data and requires data regeneration.

Using the concept of object-oriented programming (OOP), the Pavement Analysis Assistant Program (PAAP) was developed during the study in a project of the National Cooperative Highway Research Program (NCHRP) [5]. PAAP can be used in preparing load data for FEA in pavement studies, retrieving results directly from FEA output, and calculating distortion parameter of a pavement surface from FEA results or field measured data. Given the wheel wander distance, the loading time distribution can be calculated using a normal distribution [6]. With a small amount of configuration information provided in advance, such as pavement surface nodes, tire configuration, and contact stresses, the loading time distribution corresponding to each of the stress levels can be dynamically generated. The loading data thus generated can directly be written into FEA input file for analysis. After finite element analysis, the results are directly retrieved from FEA output for further processing.

PAAP was developed using the Java programming language and is object-oriented, graphical user interfaced, and platform independent. It was successfully used in the project NCHRP 1-34A [5] to develop a new pavement failure criterion.

1

A.J. Simpson, J.F. Daleiden, W.O. Hadley, "Rutting analysis from a different perspective", Transportation Research Record 1473, Transportation Research Board - National Research Council, Washington, D.C., 1995.

2

H. Fang, J.E. Haddock, T.D. White, A.J. Hand, "On the characterization of flexible pavements rutting using creep model based finite element analysis", Finite Elements in Analysis and Design, (in press, 2004). doi:10.1016/j.finel.2004.03.002

3

R. Buiter, W.M.H. Cortenraad, A.C. van Eck, H. van Rij, "Effects of transverse distribution of heavy vehicles on thickness design of full-depth asphalt pavements," Transportation Research Record 1227, Transportation Research Board - National Research Council, Washington, D.C., 1993.

4

M. de Beer, C. Fisher, F.J. Jooste, "Determination of pneumatic tire/pavement interface contact stresses under moving loads and some effects on pavements with thin asphalt layers," Proceedings of 8th International Conference on Asphalt Pavements, Seattle, Washington, 1, 129-139, 1997.

5

T.D. White, J.E. Haddock, A.J. Hand, H. Fang, "Contributions of pavement structural layer to rutting of hot mix asphalt pavements," NCHRP Report 468, National Cooperative Highway Research Program, Transportation Research Board - National Research Council, Washington, D.C., 2002.

6

J. Hua, "Finite element modelling and analysis of accelerated pavement testing devices and phenomenon," Ph.D. dissertation, Purdue University, August 2000.

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