Nonlinear dynamic computer modeling of flexible pavements

Loads generated by traffic and by nondestructive testing devices on pavements are dynamic in nature. Current computer models for design and analysis of flexible pavements are based on static analysis which ignore the inertia of the pavement. A nonlinear dynamic finite element computer model called DYNARK has been developed to aid the routine design and analysis of flexible pavements. Three major achievements have been accomplished in this research. First a user friendly computer model has been implemented for dynamic non-linear analysis of flexible pavements. The computer model is a finite element based program and it can be executed in the UNIX and DOS platforms. The development of the recent computer technology will make it easier to execute this program in the personal computers. Second, a concept of utilizing a flexible boundary in pavement analysis and two different non-linear models for the characteristics of granular base are implemented in this model. The non-linearity of the subgrade material is also taken into account. Finally, a relationship between the dynamic analysis results and the static analysis results has been developed. These relationships were developed by performing regression analysis for the output database. Also a relationship has been developed for the backcalculation of the resilient modulus from the FWD deflection basins.; In the DYNARK computer program, the pavement is represented by an axisymmetric finite element model. The finite element mesh for the DYNARK program can be easily generated by the user. Loading function is assumed as a half sine wave in this model. This represents the moving wheel load and also the FWD loading. A numerical step by step integration procedure called Newmarks's constant average-acceleration scheme was used for the solution of the dynamic equilibrium equation. The DYNARK program incorporates the viscous damping for the infinite media to make it as a finite media. An energy absorbing boundary was modeled by prescribing a set of normal and tangential stresses on the boundary. Two different non-linear models for the characteristics of granular base are implemented. The stress adjustment by Mohr Coulomb's failure criterion and the Stress Ratio models are implemented in the DYNARK computer model. The non-linearity of the subgrade is also taken into account.; It is been shown in this study that the FWD deflection basins are reproduced by dynamic analysis deflection basins for the flexible pavements. Since the loading on top of the pavement structure is dynamic in nature, the dynamic analysis results tend to reflect the true behavior of the flexible pavements. Therefore the use of dynamic model developed in this study may lead to better methods design and rehabilitation of flexible pavements.