Dynamic stability of columns subjected to follower loads : A survey

The paper examines the dynamic response of flexible conventional pavement systems to single wheel traffic loads in terms of the pavement design criteria, namely the fatigue strain at the bottom of the asphalt concrete layer and rutting strain at the top of the subgrade material. Model setup including geometry, boundary conditions, and load wave characterization are presented. The effect of elastoplasticity of the base material and elastoplasticity with strain hardening of the subgrade material on the dynamic response of the pavement system are first investigated. A detailed model parametric study then follows to show the effect of the base strength and thickness and the subgrade quality on the fatigue and rutting strains and the vertical surface deflection. The study, conducted with program ADINA, employs a three-dimensional, implicit dynamic, finite element method.

Three-Dimensional Dynamic Analysis of Flexible Conventional Pavement Foundation

To develop a rigorous, mechanistic design method for asphalt overlays, one must have a method to accurately determine the response of the overlay system to various load conditions. This paper presents a cutting-edge nonlinear three-dimensional finite-element modeling approach for asphalt overlay analysis, including a viscoelastic constitutive model and realistic traffic and environmental load conditions. These tools were used to analyze a proposed reflective crack control system for Taxiway E at the Greater Peoria Regional Airport (GPRA), involving a base-isolating interlayer mixture used in conjunction with a glass-fiber reinforcement layer. The use of a base-isolating interlayer below the asphalt overlay was found to greatly reduce tensile and shear stresses in the asphalt overlay. Based upon expected critical cooling events and design aircraft at GPRA, critical overlay and interlayer stresses were found to be predominantly load associated. The base-isolating interlayer was predicted to develop localized stresses in the vicinity of the existing crack well beyond the yield threshold, based upon linear viscoelastic analysis. This suggests the importance of designing a tough, ductile interlayer mixture that can tolerate localized yielding under repeated load applications.

Analysis of Reflective Crack Control System Involving Reinforcing Grid over Base-Isolating Interlayer Mixture

A series of finite element (FE) simulations are carried out to evaluate the benefits of integrating a high modulus geosynthetic into the pavement foundation. The simulations are conducted under a parametric study to investigate the beneficial effects of geosynthetic reinforcement to the fatigue and rutting strain criteria, and to determine how such effects are influenced by the base quality and thickness as well as the subgrade quality. Three locations of the geosynthetic reinforcement are studied, namely the base–asphalt concrete interface, the base–subgrade interface, and inside the base layer at a height of 1/3 of its thickness from the bottom. It is found that placing the geosynthetic reinforcement at the base–asphalt concrete interface leads to the highest reduction of the fatigue strain (46–48%). The placement of geosynthetic reinforcement in thin bases is particularly effective; the highest decrease of rutting strain (16–34%) occurs when the reinforcement is placed at a height of 1/3 of the base th...

3D FE Analysis of Flexible Pavement with Geosynthetic Reinforcement

Constitutive equations based upon stress dependent moduli, like K-θ and Uzan-Witczak, are widely used to characterize the resilient response of granular materials for the analysis and design of pavement systems. These constitutive models are motivated by the observation that the granular layers used in pavement structures shake down to (nonlinear) elastic response under construction loads and will, therefore, respond elastically under service loads typically felt by these systems. Due to their simplicity, their great success in organizing the response data from cyclic triaxial tests, and their success relative to competing material models in predicting the behavior observed in the field, these resilient modulus constitutive models have been implemented in many computer programs used by researchers and design engineers. This paper provides an analysis of the nonlinear solution algorithms that have been used in implementing these models in a conventional nonlinear 3D finite-element framework. The analysis s...

Analysis and implementation of resilient modulus models for granular solids

In this paper, we examine some of the essential aspects of modeling pavement structures with three-dimensional finite element analysis. Because three-dimensional problems are so large, special care must be taken to optimize mesh geometry. We describe three issues in mesh construction that have important impacts on overall problem size: (1) mesh refinement, (2) domain extent, and (3) element size transition. An algorithm for computation of the equivalent nodal loads for arbitrary tire prints with arbitrary orientation relative to the mesh is presented. Decoupling the load computation from the problem of mesh construction leads to more efficient meshes and allows efficient resolution for different gear positions.

Finite element procedures for three-dimensional pavement analysis

The structural behavior of an airfield pavement system under multiple heavy wheel loads is a big concern with new generation of aircraft. Interactions between wheels are expected to be important because of the relatively small wheel spacing (145 cm for a B-777) and high tire pressures (1.5 MPa). Three-dimensional finite element analysis can help to understand the complex behavior of a pavement under multiple wheel loads. This paper is a case study in which we examine various loading patterns and positions with different material properties and interface conditions. The section studied is modeled after a section of the Denver International Airport. Comparisons of maximum bending stresses and displacements from different landing gear configurations (single, tandem, dual-tandem, and tri-tandem) are made. An edge loading case was found to be the most critical case with respect to maximum stresses and the amount of wheel load interaction.

Q. H. Zuo

Papers

Finite element procedures for three-dimensional pavement analysis

Three-dimensional finite element study of wheel load interaction

Conditions for bifurcation of a cantilever beam subjected to generalized follower loads: Geometrically exact approach