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A textbook style development of viscoplasticity is presented. For completeness, the report also includes a detailed review of plasticity and viscoelasticity. The combination of plasticity and viscoelasticity is the basis for the so-called viscoelastic-plastic model developed herein. Other combo- viscoplastic models are also introduced. Each constitutive model is introduced with conceptual one-dimensional stress-strain models and then generalized for multidimensional stress space. Furthermore, each model is cast in an incremental form appropriate for numerical solution techniques. Finite element algorithms are outlined for incorporating these nonlinear constitutive models into boundary value problems. In particular, tangent stiffness and initial strain methods are discussed. The viscoelastic-plastic model is compared to experimental data for plexiglas and sea-ice to illustrate the versatility of the model in replicating nonlinear creep and flow of these materials. Moreover, the identification of the model parameters are shown to be no more difficult than the identification of parameters for the classical theories of plasticity and viscoelasticity.

Two subgrades and four rigid pavement test sections were constructed and instrumented to recover experimental information of soil/rigid pavement behavior beneath static loadings. Pavement deflections and pavement/soil strain data were recorded for incremental static loads applied to a 30 inch diameter steel plate. Tests were conducted for comparison of experimentally collected data with Westergaard and elastic layer analyses of the test sections to investigate whether a consistent mathematical relationship exists between the two methods of analysis. To this end material characterizations were carried out for the component materials in the 4 different pavement sections and analytically predicted and experimentally obtained response data were compared.

The report is concerned with the design of concrete overlays for flexible pavements. The conventional Westergaard analysis for the design of concrete overlays is reviewed and its weaknesses are enumerated. A review of layered theory indicated that an elastic layered solid approach to overlay design would predict an overlay thickness thinner than that suggested by Westergaard and, thus it offers a dollar savings in construction costs without a loss in rated load capacity. A field test section consisting of overlays of different thicknesses was constructed and load tested to evaluate the appropriateness of the new theoretical approach and also to verify the assumed failure criterion. A limited strain concept was selected as the failure mode; that is, the maximum tensile strain in the concrete at the overlay-pavement interface should be limited to a prescribed maximum value. (Author)

Increasing operational use od ice areas in polar regions has heightened the requirement for improved knowledge and techniques to analyze the behavior of sea ice. Previous studies on elastic behavior are reviewed with emphasis placed on plate analysis. Classical plate theory and the finite element method are compared in analyzing ice plates, with special attention given to sea-ice airfields. Since elastic analysis is not totally representative of actual ice behavior, a general formulation is presented which gives the assumptions and procedures for both viscoelastic and nonlinear domains of sea-ice behavior. A laboratory program is being initiated to determine material properties that are necessary to extend sea-ice analysis into the inelastic range. (Author)