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Probability, Reliability and Statistical Methods in Engineering Design

This work presents a repeatable semi circular bending (SCB) fracture test to evaluate the low temperature fracture resistance of asphalt mixture. The fracture resistance of six asphalt mixtures, which represent a combination of factors such as binder type, binder modifier, aggregate type, and air voids, and two testing conditions of loading rate and initial notch length, was evaluated by performing SCB fracture tests at three low temperatures. Fracture energy was calculated from the experimental data. Experimental results indicated strong dependence of the low temperature fracture resistance on the test temperature. Experimental plots and low coefficient of variation (COV) values from three replicates show a satisfactory repeatability from the test. The results of the analysis showed that fracture resistance of asphalt mixtures is significantly affected by type of aggregate and air void content. Experimental results also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Analysis of result also indicated that both the loading rate and initial notch length had significant effect on the fracture energy at the highest test temperature, whereas the effect was strongly diluted at the two lower temperatures. No clear trend was found with the fracture peak load from either the effect of loading rate or notch length.

Using Semi Circular Bending Test to Evaluate Low Temperature Fracture Resistance for Asphalt Concrete

This paper describes the quantification of three-dimensional tyre/pavement contact stresses for vehicle tyres. The Vehicle-Road Surface Pressure Transducer Array (VRSPTA) system was developed to measure contact stresses under moving loads, i.e., Stress-In-Motion (SIM). Prediction equations for quantification of these stresses, based on tyre inflation pressure and loads for seven different tyre types, are given. Tyre inflation pressure predominantly controls the vertical contact stresses on the pavement at the tyre centre, whereas the tyre load controls those at the tyre edges. Analysis indicated that during instantaneous overloading/under-inflated conditions the maximum strain energy of distortion (SED) in the asphalt surfacing occurs close to the tyre edges, while under instantaneous uniform vertical stress conditions the SED is within the asphalt surfacing at the tyre centre. In addition to improved load/contact stress idealization for modelling, this finding may have important implications for the design of relatively thin asphalt surfacing layers for pavements.

Determination of pneumatic tyre/pavement interface contact stresses under moving loads and some effects on pavements with thin asphalt surfacing layers

1. Introduction 2. Types of Concrete Pavements 3. Performance 4. Subgrades, Subbases, and Drainage 5. Selection of Concrete Materials 6. Mixture Design and Proportioning 7. Design Fundamentals 8. Highway Pavement Design 9. Light-Duty Pavement Design 10. Airport Pavement Design 11. Industrial Pavement Design 12. Subgrade and Subbase Construction 13. Paving 14. Finishing, Texturing, and Curing 15. Concrete Pavement Maintenance 16. Rehabilitation and Overlays

Concrete Pavement Design, Construction, and Performance

This paper provides an in‐depth synthesis of knowledge acquired over the last several decades pertaining to the analysis and design of doweled slab‐on‐grade pavement systems. This task is accomplished on the basis of rigorous, theoretically sound engineering principles, and relies extensively on the application of dimensional analysis for the interpretation of finite element data pertaining to the behavior of doweled joints. A design procedure is derived that allows, for the first time, the determination of the dowel diameter and spacing required to achieve a desired level of load transfer, or a threshold value of dowel‐concrete bearing stress. The proposed approach eliminates the need for any a priori assumptions with respect to the distribution of dowel shear forces. An efficient and general method for the backcalculation of the modulus of dowel reaction, K, from deflection data is also suggested. These research findings constitute a mechanistic structural model for JPCP and contribute significantly tow...

Analysis and Design of Doweled Slab‐on‐Grade Pavement Systems

A finite element investigation was made of the behavior of jointed or cracked pavement systems equipped with a pure-shear load transfer mechanism, such as aggregate interlock. Dimensional analysis was used in the interpretation of the data, leading to a general definition of the relative joint stiffness of the pavement system in terms of its structural characteristics. Results obtained in this study were verified by comparisons with earlier published field, laboratory, and analytical information. The investigation demonstrated that deflection load transfer efficiency is related to stress load transfer efficiency and that this relationship is sensitive to the size of the applied loading (or to the gear configuration). A simple back calculation procedure is outlined to evaluate the in situ joint stiffness of such pavements. Pure-shear load transfer devices are shown to be particularly desirable under a combined externally applied and thermal loading condition, since they offer no additional restraint to longitudinal curling.

Aggregate interlock: a pure-shear load transfer mechanism

A consistent and theoretically rigorous approach is presented, using the principles of dimensional analysis, and leading to a closed-form back-calculation procedure for a two-layer slab-on-grade pavement system. The equations required are derived and evaluated for four fundamental combinations of loading and support conditions. A short computer program has been coded, called ILLI-BACK, to implement the method on a personal computer. The execution time per back-calculation is trivial (a fraction of a second). This procedure simplifies considerably the effort required in interpreting nondestructive deflection data. It is much more efficient and accurate than current approaches, allowing the use of any one of the measured sensor deflections in the back-calculation process. The concept proposed is powerful and versatile, and can easily be adapted for a wide variety of other applications, involving both rigid and flexible pavement systems.

Dimensional analysis in ndt rigid pavement evaluation

The pioneering analytical work of Harold Malcom Westergaard (1888-1950) has been at the heart of slab-on-grade pavement design since the 1920s. Every code of practice published since then makes reference to the "Westergaard solutions." These solutions are only available for three particular loading conditions (interior, edge, and corner) and assume a slab of infinite or semi-infinite dimensions. Since their first appearance, beginning in the early 1920s, Westergaard equations have often been misquoted or misapplied in subsequent publications. To remedy this situation, a reexamination of these solutions using the finite element method is described in this paper. A number of interesting results are presented: (a) Several equations ascribed to Westergaard in the literature are erroneous, usually as a result of a series of typographical errors or misapplications, or both. The correct form of these equations and their limitations have now been conclusively established. (b) Westergaard's original equation for edge stress is incorrect. The long-ignored equation given in his 1948 paper should be used instead. (c) Improved expressions for maximum corner loading responses have been developed. (d) Slab size requirements for the development of Westergaard responses have also been established.

Westergaard solutions reconsidered

: This study is concerned with analytical and numerical procedures applied to slab-on-grade pavements, treated as plates on elastic foundation, with particular emphasis on the possibilities offered by the automated digital computer. In the first part of the report, analyses employing the dense liquid foundation are examined. This includes an exhaustive reexamination of Westergaard's work, which established conclusively the correct form of the Westergaard equations and pointed out that the New edge stress formula should be used. Closed-form solutions for a plate on a dense liquid or an elastic solid foundation are assembled in a computerized compendium called WESTER. The second part of the study focuses on elastic solid analyses of the same problem. Pickett's Chart for edge stress is recalculated using computerized numerical integration, and the results is incorporated in computer program H51ES. Three additional computer codes are developed: 1) A method using the concept of concordant deflections for axisymmetric plates (program CFES); 2) A finite difference approach for rectangular plates (program FIDIES); and 3) A finite element solution for rectangular plates (incorporated into program ILLI-SLAB).

Anastasios M. Ioannides

Papers

Analysis and Design of Doweled Slab‐on‐Grade Pavement Systems

Aggregate interlock: a pure-shear load transfer mechanism

Dimensional analysis in ndt rigid pavement evaluation

Westergaard solutions reconsidered

Analysis of Slabs-on-Grade for a Variety of Loading and Support Conditions.