Proceedings of the 27 th Southern African Transport Conference (SATC 2008) 7 - 11 July 2008 ISBN Number: 978-1-920017-34-7 Pretoria, South Africa Produced by: Document Transformation Technologies cc Conference organised by: Conference Planners SOME FUNDAMENTAL DEFINITIONS OF THE ELASTIC PARAMETERS FOR HOMOGENEOUS ISOTROPIC LINEAR ELASTIC MATERIALS IN PAVEMENT DESIGN AND ANALYSIS M. De Beer and J. W. Maina CSIR Built Environment, P.O. Box 395, Pretoria, 0001 +2712841-2953, +2712842-7114, Email: [email protected] ABSTRACT This paper is a brief introduction to some of the well known fundamental engineering properties of homogeneous isotropic linear elastic materials. It specifically shows the relationships between different elastic moduli. It covers some of the extensive (but not so well known) relationships between the various moduli of these materials and also illustrates the importance of parameters such as Poisson’s Ratio. The aim of the paper is to summarise the fundamental elastic properties of the above types of materials, as well as their interrelationships and to use these as background to engineering in road modelling and simulation. An additional aim is to show that moduli measured under different conditions should probably be treated differently, such as creep speed measurements of elastic surface deflection basins carried out with the Benkelman Beam (BB) (or Road Surface Deflectometer (RSD)) associated with Heavy Vehicle Simulator (HVS) testing, and those measured under relatively short time impulse loading (i.e. seismic) by means of the Falling Weight Deflectometer (FWD). 1. INTRODUCTION 1.1 Background Rehabilitation design and analysis of existing road structures require appropriate equipment for testing and for associated evaluation methodologies. Current state-of-the- art equipment includes apparatus such as the Falling Weight Deflectometer (FWD), Rolling Deflectometer (RD), Deflectographs, high speed deflectometers, Benkelman Beam (BB), Multi-Depth Deflectometers (MDD) etc. for the measurement of mainly elastic (i.e. recoverable) surface (and in-depth) deflection profiles of a road structure under pre- defined loading conditions. These deflection results are then typically used in back- calculation routines for multi-layered road pavement systems based on the theory of homogenous isotropic linear elasticity. As this theory is used as an approximation of reality and since most solutions are non-unique, there are many practical problems associated with the theoretical back-calculation technique. A major problem is the allocation of the appropriate input engineering parameters such as the effective elastic moduli and the associated Poisson’s Ratios for the materials based on the theory of linear elasticity. This paper addresses some of the fundamental definitions of these elastic parameters, especially those associated with creep (slow speed) tyre loading conditions as opposed to those done at higher speed conditions (including impulse loading such as with the FWD). It is shown that Young’s moduli under seismic impulse small-strain loading can theoretically be as much as 3.5 times greater than those done at slower speed (and higher strain) conditions on the same material, depending on the assumed Poisson’s Ratio. Some practical guidelines are given here for the appropriate use of these parameters for the
SOME FUNDAMENTAL DEFINITIONS OF THE ELASTIC PARAMETERS FOR HOMOGENEOUS ISOTROPIC LINEAR ELASTIC MATERIALS IN PAVEMENT DESIGN AND ANALYSIS
Jun 20, 2023
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