Shmuel L. Weissman

Selection of Laboratory Test Specimen Dimension for Permanent Deformation of Asphalt Concrete Pavements

Permanent deformation of asphalt concrete pavements is a critical distress mechanism. Efforts are currently being made to understand, analyze, and predict permanent deformation response. To characterize asphalt concrete, laboratory testing is routinely performed. The concept of the representative volume element for determining the minimum specimen dimensions to obtain reliable and repeatable laboratory test data is discussed here. Two conceptual laboratory tests that are currently used to characterize asphalt concrete—the restricted triaxial test and the simple shear test at constant height—are also discussed. The imperfections of both tests are investigated and recommendations for specimen size and the aspect ratio for each of the tests are made.

INFLUENCE OF TIRE-PAVEMENT CONTACT STRESS DISTRIBUTION ON DEVELOPMENT OF DISTRESS MECHANISMS IN PAVEMENTS

It is demonstrated that accurate characterization of tire-pavement contact stress distribution is important for the correct prediction of distress evolution in flexible pavements. First, an analysis of tire imprints and measured tire-pavement contact stress distribution leads to the conclusion that the shape of the contact area depends on the load and tire pressure and that the contact stress distribution is nonuniform. Second, software for a linear-layered elastic medium contrasts the stress distribution in a pavement due to two loads: a uniformly distributed pressure on a circular area and a distribution reported earlier by de Beer and Fisher. The analysis herein demonstrates that nonuniform contact stress distribution leads to considerably larger stresses in the pavement relative to the uniform stress distribution case. Consequently, both rut and crack evolution prediction would be different if they were based on true distribution rather than on the uniform distribution assumption. It is also shown that for overloaded tires, the contact area is rectangular, where the width of the contact is a tire property independent of the applied load. Therefore, approximating the load as a uniformly distributed stress over a circular area may lead to erroneous prediction regarding the transverse or longitudinal orientation of cracks.

A unified approach to mixed finite element methods: application to in-plane problems

Abstract A general method to treat internal constraints within the context of mixed finite element methods has been presented in previous work. The underlying idea is to constrain the assumed stress and strain fields to satisfy the homogeneous equilibrium equations in a weak sense and thus satisfy a priori the internal constraints. This method is now applied to generate four-node plane stress/strain elements. For these elements, it is proved that locking at the nearly incompressible limit (plane strain) is avoided at the element level. The proposed elements are shown to yield excellent results on a set of standard problems. Furthermore, excellent stresses are obtained at the element level.

Four-node axisymmetric element based upon the Hellinger-Reissner functional

Abstract The Hellinger-Reissner functional is used to formulate axisymmetric elements of the correct rank using seven and eight parameter stress fields. The resulting elements exhibit excellent performance in bending problems and at the nearly incompressible limit. The stress field is developed in conjunction with an orthogonal projection so that the resulting stiffness matrix requires only block diagonal inversion. Several numerical examples are given to demonstrate the performance of the suggested formulation.

Mixed formulations for plate bending elements

Abstract Plate bending elements, based on the Reissner-Mindlin plate theory, are formulated via the Hu-Washizu variational principle, including the Hellinger-Reissner functional as a special case. It is proven that these elements avoid the well-known shear locking behavior at the thin plate limit. To obtain this objective, the assumed stress and strain fields are constructed to satisfy a priori the homogeneous equilibrium equations in a weak sense. The proposed elements are shown to perform well on a set of standard problems.