B Frank McCullough

Dynamic response of plate on viscous Winkler foundation to moving loads of varying amplitude

The dynamic displacement and stress responses of a plate of infinite extent on a viscous Winkler foundation subjected to moving tandem-axle loads with amplitude variation have been investigated. Formulations have been developed in the transformed field domain using a triple Fourier transform in time, space, and moving space for moving loads with arbitrary amplitude variation, and a double Fourier transform in space and moving space for the steady-state response to moving harmonic loads. The rigid and flexible pavement systems have been selected as models of the plate on viscous Winkler foundation. The effects of viscous damping, load velocity, load frequency, and phase between the front- and rear-axle loads on the maximum deflection and stress and on the deflection and stress distributions near the loads have been investigated. The analysis results considering viscosity of foundation show significant differences from those obtained with an elastic system. The variation in the load amplitude caused by the surface roughness and the difference in the phase between the front- and rear-axle loads can make the maximum deflection and stress considerably larger.

Importance of Concrete Temperature Control During Concrete Pavement Construction in Hot Weather Conditions

The development of high concrete temperatures could cause a number of effects that have been shown to be detrimental to long-term concrete performance. High concrete temperatures increase the rate of hydration, thermal stresses, the tendency for drying shrinkage cracking, and permeability and decrease long-term concrete strengths and durability as a result of cracking. Data from the Texas Rigid Pavement database were analyzed to reveal whether there are increased numbers of failures as the air temperature at placement increases. It was shown that this was the case for both major coarse aggregate types: limestone and siliceous river gravel. The results of the analysis emphasize the importance of concrete temperature control during concrete pavement construction in hot weather conditions. Most states specify a maximum concrete temperature at placement to mitigate the detrimental effects of placement during hot weather. The specified limit remains the same irrespective of the type of mineral or chemical admixtures used. To produce specifications that encourage contractor innovation and the use of improved materials, modern specifications should account for these materials to ensure improved concrete performance under all placement conditions. To provide improved performance for sections paved under hot weather conditions, it is proposed that the continuously reinforced concrete pavement reinforcement standards be redesigned to provide steel quantities for specific use during hot weather conditions and that an end-result specification that limits the maximum in-place concrete temperature during hydration be implemented.

Dynamic Stress Response of Concrete Pavements to Moving Tandem-Axle Loads

The dynamic stress response of concrete pavements subjected to moving tandem-axle loads of constant amplitude and harmonic and arbitrary variations was investigated. The concrete pavement was modeled using a plate of infinite extent on a viscoelastic foundation. Formulations were developed in the transformed field domain using (a) a double Fourier transform in space and moving space for moving loads of constant amplitude and for the steady-state response to moving harmonic loads and (b) a triple Fourier transform in time, space, and moving space for moving loads of arbitrary variation. The effects of viscous damping, velocity, load frequency, and phase between front- and rear-axle loads on the maximum stress and the stress distribution were analyzed. Without viscous damping, the effects of velocity and frequency, within practical ranges, on the stresses are negligible; however, with viscous damping, those effects are significant. Since materials used in various pavement layers possess damping characteristics, wheel load stresses can vary considerably because of velocity and load frequency. The increase in wheel load variations and corresponding concrete stresses can be significant if the roughness of the pavement surface is not controlled. The difference in the phase angles between front- and rear-axle loads can considerably increase the maximum stress; therefore, the use of tandem-axle loads and dynamic analyses is necessary to obtain the accurate stresses because the phase effect cannot be obtained with single-axle loads or static analyses.

Mechanistic Modeling of Continuously ReinforcedConcrete Pavement

The use of continuously reinforced concrete pavement (CRCP) has increased in recent years in urban areas of Texas because CRCP provides a long-lasting pavement requiring little maintenance. A computer program, known as CRCP-10, has been developed using finite element formulations, transformed field domain analysis, and probability theories to analyze the behavior of CRCP. This mechanistic model predicts the crack spacing distribution and time histories of mean crack spacing/width and of longitudinal steel stress. The CRCP-10 computer program considers nonlinear variations of temperature and drying shrinkage through the depth of the concrete slab, curling and warping effects, concrete creep effect, nonlinear bond-slip between concrete and steel bars, changes in material properties with time, and moving dynamic tandem-axle loads. This paper presents details of the mechanistic modeling of CRCP and applications of CRCP-10 to various problems.

IDENTIFICATION OF PAVEMENT FAILURE MECHANISMS AT FHWA ACCELERATED LOADING FACILITY ULTRATHIN WHITETOPPING PROJECT

In 1998 eight test lanes of ultrathin whitetopping (UTW) were constructed over existing hot-mix asphalt (HMA) pavements at FHWA’s Accelerated Loading Facility (ALF) located at the Turner-Fairbank Highway Research Center in McLean, Virginia. Various combinations of thicknesses, joint spacings, fiber reinforcement, and types of HMA base were used. In spring 2000 the loading experiment of these pavements was completed, and the analysis of behavior and performance was begun. A summary of some of the pavement distresses observed at the ALF is presented, and hypothesized failure mechanisms are identified, providing an addition to the state of the knowledge with respect to the actual life cycle of UTW pavements.

PRECAST PRESTRESSED CONCRETE PAVEMENT PILOT PROJECT NEAR GEORGETOWN, TEXAS

The use of precast concrete is rapidly becoming a viable method for repair and rehabilitation of portland cement concrete pavements, with several projects under construction or in development throughout the United States. Construction with precast concrete offers numerous benefits over conventional cast-in-place pavement construction. Most notable is how quickly a precast pavement can be opened to traffic. Precast panels can be placed during overnight or weekend operations and opened to traffic almost immediately. In addition, because precast panels are cast in a controlled environment, the durability of a precast pavement is also improved. In March 2002, the Texas Department of Transportation completed construction of a precast pavement pilot project aimed at testing and further developing a precast pavement concept developed by the Center for Transportation Research at The University of Texas at Austin. This project was constructed on a section of frontage road along Interstate 35 near Georgetown, Texas. The project incorporated the use of posttensioned precast concrete panels. The panels were posttensioned in place not only to tie all the panels together but also to reduce the pavement thickness required and improve durability. The finished pavement demonstrated not only the viability of precast pavement construction but also the benefits of incorporation of posttensioning. Although the project was constructed without the time constraints and complexities that will eventually need to be considered for precast pavement construction, it ultimately helped to develop viable construction procedures for future precast prestressed concrete pavements.

In Situ Material Properties from Dynamic Deflection Equipment

Dynamic deflection equipment presents a very practical and cost-effective approach for nondestructive testing and evaluation of pavement-subgrade systems. The in situ Youngs moduli are calculated by the inverse application of layered elastic theory to the measured dynamic deflection data. This paper discusses some of the fallacies associated with this iterative approach. The calculated moduli are user dependent and nonunique if the user inputs the initial set of moduli to start iteratives. A proven methodology to ensure uniqueness of the moduli is the generation of seed moduli as the function of measured deflections and radial distances of the sensors. The FPEDD1 (for pavements with asphalt concrete surfacings) and RPEDD1 (for rigid pavements) computer program incorporate this methodology. The predictive equations used to generate seed moduli are based on numerous layered theory solutions and are therefore applicable to any region and soil condition. This paper describes the approaches used in these programs to estimate nonlinear moduli for granular layers and subgrade soil, and considers rock layers. Examples are presented for in situ material properties from dynamic deflection data measured on a variety of pavement-subgrade systems. It is shown that an appropriate analysis technique yields comparable pavement moduli from the dynamic deflection data measured by vibratory or impulse loading equipment.

Constructing High-Performance Concrete Pavements with FHWA HIPERPAV Systems Analysis Software

HIPERPAV (high-performance paving) is a concrete paving software product developed jointly by FHWA and The Transtec Group, Inc., and is intended to serve as a tool in the proper selection and control of the factors affecting concrete pavement behavior at early ages. Adequate selection and control of these factors will ensure good performance throughout the design life of the pavement. Praised by industry, agencies, and academia, HIPERPAV is the first software tool of its kind to provide real control over concrete pavement design and construction. With HIPERPAV, materials, pavement design, and construction operations can now successfully be integrated into one easy-to-use Windows based software package. This integration captures all aspects of a concrete pavement construction project and provides a real systems approach to analysis of the first 72 h after construction. With a true systems approach, the development of stresses and strength in concrete pavement can be assessed during these critical first 72 h to maximize quality, increase long-term performance, boost productivity, and optimize pavement options. A brief history of the development, validation, and implementation of the HIPERPAV software to date is presented.