IMPROVED MODELS FOR STRUCTURAL AND FATIGUE ANALYSIS OF CONCRETE PAVEMENT

Abstract

This study examines the structural models and fatigue relationships currently in use for concrete pavement analysis, and aims to develop improved analysis models for both. The main objective of this study is to develop, based on advanced theories or new concepts, improved models for: 1) analysis of concrete pavement response to traffic loading, 2) analysis of concrete pavement response to thermal warping, and 3) analysis of fatigue behaviour of concrete pavements under a combination of traffic loading and thermal warping. An improved model for analysis of concrete pavement response to traffic loading is developed based on Reissner (1945) thick plate theory and Pasternak (1954) foundation model. A concrete pavement system subjected to traffic loading is idealised as a three-slab system with shear transfer along two joints and loaded at the middle slab by arbitrary vertical loads. Fundamental equations are then derived in terms of Reissner thick plate theory and Pasternak foundation model. Finally, an analytical solution to the problem is arrived at by means of the method of superposition as follows: a) choosing elemental slabs for the problem, b) deriving the corresponding solutions of these elemental slabs with unknown coefficients, c) expressing the solution of each slab of the 3-slab system as superposition of the solutions of appropriate elemental slabs, and d) determining the unknown coefficients in the solutions by forcing the solutions to satisfy the boundary conditions of the three-slab system. This proposed model can consider effects of transverse shear deformation in pavement slabs, interlocking action in the subgrade and joint transfer between pavement slabs. The solutions of the proposed model are verified by comparing them with those of other existing models. The effects of joint transfer and interlocking action in subgrade on pavement response are investigated by means of the efficiency of joint shear transfer Rw and the shear modulus of subgrade Gb respectively. The effect of transverse shear deformation of slab on pavement response is investigated by comparing the proposed thick plate solution to Westergaard's thin plate solution. Two improved models for analysing thermal warping stresses in concrete pavements are developed. A model for thin plate on Pasternak foundation is derived based on the classical thin plate theory. It can estimate thermal warping stresses in concrete pavements with consideration of the interlocking action of subgrade. With the proposed thin plate model, the influence of interlocking action of subgrade on the thermal warping stresses in slabs is investigated. A model for thick plate on Pasternak foundation is also developed in terms of the Reissner thick plate theory. It can estimate thermal warping stresses in concrete pavements with consideration of not only interlocking action in subgrade but also transverse shear deformation in pavement slabs. With the thick plate model, the limitations of the thin plate model are examined. The proposed models for concrete pavement response under traffic loading and thermal warping are verified by comparing them with those of full-size experiments. An empirical relationship between the modulus of subgrade reaction k and shear modulus of subgrade Gb is developed so that the shear modulus of foundation can be estimated from modulus of subgrade reaction k. By means of this relationship, the models for concrete pavements under traffic loading and thermal warping respectively are compared with measurements from documented full-size experiments. A fatigue model for concrete pavement is presented based on a laboratory study of the flexural fatigue strength of 78 plain concrete beams. The probability distribution of the fatigue test data is analysed by introducing a new concept of equivalent fatigue life. A laboratory fatigue relationship is developed to include the effects of stress ratio and stress level. It allows a statistical description of fatigue life in terms of both stress level and stress ratio. Using the developed fatigue model, the fatigue behaviour of concrete pavements under the combined action of traffic loading and thermal warping is analysed.