Tire-pavement Contact Research Articles

Modelling Tensile Strain Response in Asphalt Pavements

ABSTRACT Traditionally, HMA pavement designs and modeling methods have historically been based on the fundamental assumption that fatigue cracking generally initiates at the bottom of the HMA layer due to excessive tensile stresses/strains, and then propagates upwards to the surface. However, fatigue cracking can either be bottom-up or top-down initiated depending on the location of the maximum horizontal tensile stresses and strains in the HMA layer. Various factors such as the pavement structure and wheel/tire loading configurations influence both the location and magnitude of the fatigue crack-related tensile strains that are induced in the HMA layer. In this study, the influence of these factors on the tensile strains responses and potential location of fatigue crack initiation in HMA pavements was investigated. To address the non-uniformity distribution of the tire-pavement contact pressure (TPCP), including the vertical tire-pavement contact pressure and horizontal tire-pavement stress, a three-dimensional finite element program was utilized for the computational simulations and numerical analyses. Specifically, the actual TPCP of different tire types and tread patterns measured under variable load levels and tire inflation pressures were utilized to evaluate and analyze the potential locations of maximum tensile strains in terms of fatigue crack initiation. The results showed that the longitudinal and low latitudinal tire-pavement stress hardly influence the maximum tensile strains in the HMA layer; and that the maximum tensile strains can occur either at the top or bottom (or both) of the HMA layer, thus inducing top-down and/or bottom-up fatigue crack initiation. Just like heavy-truck tire loading, the study also demonstrated that light-truck tire loading can induce excessive fatigue crack-related tensile strains in the pavement.

Interpretation of Accelerated Laboratory Testing of the Prototype Modulas Stress in Motion Sensor with the MMLS3 Load Simulator

With modern heavy vehicles using higher inflation pressures and higher axle loads the dynamic measurement of the tire-pavement contact force/stress is essential not only for tire development but also in road research for the investigation of factors which may lead to excessive damage of pavements. In this paper the results of laboratory tests with a prototype stress in motion (SIM) quartz sensor trafficked with a one-third scale load simulator (MMLS3) are presented. The tests were designed to vary parameters such as tire inflation pressure, speed, ambient temperature, lateral position, and angle to direction of travel in a controlled environment in order to isolate the influence of these parameters on the SIM sensor results. All other controllable variables remained constant while the target parameter was varied. Tire inflation pressures were calculated from these data. The laboratory tests show that the prototype sensor promises to be an effective investigative tool for SIM measurements.

Influence of vertical load models on flexible pavement response—an investigation

This paper aims to illustrate the influence of moving loads on pavement analysis, namely their characteristics and time distribution. Firstly, a state-of-the-art load model for pavement analysis is presented. Components of traffic load (contact stresses), their magnitude and time distribution, the tyre-pavement contact area and the characterization of a moving load according to dynamic and static formulations are introduced. Secondly, a study of the influence of load models (uniform vs. non-uniform distribution and non-moving vs. moving load) for pavement analysis by modelling a flexible pavement with the finite element method (FEM) is performed. The structure is modelled with DIANA software (TNO 2005), considering bituminous layers as a viscoelastic material and granular layers and foundation as a linear elastic material. The study reaches the conclusion that pavement response presents different evolutions, during loading time, depending on whether we choose a uniform or non-uniform time distribution load. Considering non-uniform distribution, the maximum value of pavement response can be much higher than those calculated for uniform distribution. It was also confirmed that the moving load character influence decreases not only with pavement depth, but also with distance from the point where the load is applied.

A Simple and Effective Laboratory Test Device for Measuring Tire-Pavement Contact Pressure

Abstract For most mechanistic response analyses of asphalt pavements, the traffic loading between the tire and the pavement is often modeled as a circular contact area with a uniform stress distribution. In reality, the tire-pavement contact pressure is hardly circular or uniformly distributed. In order to more accurately model the pavement responses under traffic loading, it is necessary to measure the actual tire-pavement contact pressure (TPCP) and then use it for pavement mechanistic response analyses. Currently there are a few devices that can be used to measure the TPCP. However, most of these existing devices have some limitations. For example one of the major disadvantages is the fact that the measured data were the pressure between the tire and a steel plate, and not between the tire and the asphalt pavement. For accurate TPCP measurements in this paper, a simple and effective static laboratory test device was developed. One of the features of this device is that the pressure sensors were inserted and suspended within the asphalt slab and the top of the sensors were kept flush with the surface at the interface with the tire. This enabled the true TPCP between the tire and the asphalt surface to be measured. Additionally, the device is relatively easy to set up and conduct the tests. Thus far, the laboratory measured TPCP results with this static test device were reasonably consistent with existing theories and assumptions about modeling the TPCP and pavement mechanistic responses.

Dynamic Analysis and in Situ Validation of Perpetual Pavement Response to Vehicular Loading

A three-dimensional (3-D) finite element (FE) model was developed to predict pavement responses to vehicular loading. The model incorporates measured tire-pavement contact stresses, continuous moving wheel loading, and hot-mix asphalt (HMA) viscoelastic characteristics. The model was fine-tuned using implicit-dynamic analysis and validated using pavement response from accelerated loading. Two tire configurations (dual-tire assembly and wide-base 455 tire) and three full-depth flexible pavement designs (HMA 152 mm, 254 mm, and 420 mm) were used in both FE modeling and accelerated loading tests. The predicted and calculated strain responses at the bottom of HMA were in agreement. Most important, the study shows that vertical shear strain in the upper 76 to 100 mm of the pavement surface is critical for thick pavement and is influenced by the 3-D tire-pavement contact stresses under each tire rib. However, the tensile strain at the bottom of HMA is affected mainly by the total wheel load. The vertical shear strain is responsible for near-surface fatigue cracking as well as HMA primary rutting. Top-down cracking could result from the local vertical shear strain in the upper 25 mm of the HMA where the effect of tire-pavement tangential stresses are the highest. In addition, the study concluded that wide-base tires cause higher longitudinal tensile strain at the bottom of HMA and compressive strain at the top of subgrade, where those responses are highly affected by the total wheel load. However, wide-base tires were found to cause less vertical shear strains near the surface than dual-tire assembly loading regardless of HMA thicknesses.

An object-oriented framework for finite element pavement analysis

In this study, we developed an object-oriented (OO) framework with interactive graphics to assist pavement studies using finite element analysis (FEA). FEA has been proven to be effective in studying various pavement failure problems; however, it is time consuming and error prone to manually generate the load sequences where non-regular tire footprints, non-uniform tire-pavement contact stresses, and transverse wheel wander distributions are used. After FEA, extracting the deformations for failure analysis is necessary but tedious. The OO framework developed in this study handles the preprocessing and postprocessing tasks for the FEA of pavements. It has a graphical user interface and is platform independent. It was successfully used in developing a new criterion for characterizing pavement failures that involved approximately four hundred different FEA simulations.

Strain Distribution in the Asphalt Layer under Measured 3-D Tire-pavement Contact Stresses

ABSTRACT Most pavement design methodologies assume the tire-pavement contact stress is equal to the tire inflation pressure and uniformly distributed over a circular contact area. However, tire-pavement contact area is not in a circular shape and the contact stress is neither uniform nor equal to the tire inflation pressure. To precisely account for the effect of actual contact stress on pavement response, this study evaluates the horizontal strains at the bottom of the asphalt layer produced by measured 3-D non-uniform stresses applied on the pavement surface. A multi-layer linear-elastic computer program, CIRCLY, was used to estimate horizontal strains in longitudinal direction and transverse direction under a number of combinations of load, tire pressure and asphalt thickness. Results show that the uniform stress model underestimates the longitudinal strains under a combination of thin surface layer and low tire pressure, and underestimates the transverse strains under a combination of thin surfacing, ...

Strain Distribution in the Asphalt Layer under Measured 3-D Tire-pavement Contact Stresses

ABSTRACT Most pavement design methodologies assume the tire-pavement contact stress is equal to the tire inflation pressure and uniformly distributed over a circular contact area. However, tire-pavement contact area is not in a circular shape and the contact stress is neither uniform nor equal to the tire inflation pressure. To precisely account for the effect of actual contact stress on pavement response, this study evaluates the horizontal strains at the bottom of the asphalt layer produced by measured 3-D non-uniform stresses applied on the pavement surface. A multi-layer linear-elastic computer program, CIRCLY, was used to estimate horizontal strains in longitudinal direction and transverse direction under a number of combinations of load, tire pressure and asphalt thickness. Results show that the uniform stress model underestimates the longitudinal strains under a combination of thin surface layer and low tire pressure, and underestimates the transverse strains under a combination of thin surfacing, low tire pressure and high wheel loading.

Effect of Measured Three-Dimensional Tire–Pavement Contact Stress on Pavement Response at Asphalt Surface

Top-down cracking results from horizontal strains at the pavement surface that are caused by high wheel loads. When horizontal strains are calculated, the tire–pavement contact stress is assumed to be equal to the tire inflation pressure and to be distributed uniformly over a circular area. In reality, tire–pavement contact stress is distributed nonuniformly over a noncircular area. Actual contact stresses vary along the longitudinal and transverse directions. For precise assessment of the effect of actual three-dimensional (3-D) contact stress on pavement response, this study evaluates the horizontal strains at the surface of the asphalt layer produced by measured 3-D nonuniform stresses. The analysis evaluates five wheel loads, five tire inflation pressures, and 12 pavement structures. A multilayer linear elastic computer program, CIRCLY, was used to estimate horizontal strains in the longitudinal and transverse directions. CIR-CLY's ability to handle normal and shear stresses at the pavement surface makes it a preferred tool compared with finite element models, which are more data and computational demanding. Strain distributions due to uniform stress were also calculated for comparative purposes. The results show that horizontal strains at the pavement surface are compressive within the contact area and tensile at the edge of or outside the contact area. The vertical contact stress and transverse contact stress have significant effects on the longitudinal strains. The vertical stress dominates the developed transverse strains. Two models were developed to estimate the surface critical horizontal strains in the longitudinal and transverse directions. These equations could serve as a tool for determination of critical combinations of asphalt thickness, wheel load, and tire pressure that the uniform stress model would grossly misestimate.

Finite element modelling of flexible pavements on soft soil subgrades

The effect of tyre pressure, wheel configuration and axle load variations of a transportation truck, on structural performance of a flexible road pavement with thin asphalt surfacing layer and soft peat soil subgrade was evaluated using the finite element method. The pavement structure was modelled as two-dimensional four-layer stratum using ANSYS/ED finite element suite. The pavement model was subjected to cyclic loadings to simulate three levels of truck wheel loads at four tyre inflation pressures of 350,490,630 and 770 kPa. Results from the model were verified using in situ full-scale test data. Model comparisons with measured full-scale test data were in good agreement, with coefficient of determination ( R 2) ranging from 0.66 to 0.92. Therefore, for known pavement material characteristics and tyre-pavement contact regime, finite element method could be used to efficiently estimate the potential distress.

Mechanistic–Empirical Study of Effects of Truck Tire Pressure on Pavement

Truck tire pressure plays an important role in the tire–pavement interaction process. As a traditional approximation method in many pavement studies, tire–pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and simply equal to the tire pressure. However, recent studies have demonstrated that the tire–pavement contact stress is far from uniformly distributed. In this study, measured tire–pavement contact stress data were input to a finite element program to compute pavement immediate responses for three tire configurations: single tires, dual tires, and dual-tire tandem axles. Computed critical pavement responses were input to pavement distress transfer functions to analyze further the effects of tire inflation pressure on pavement performance. Two asphalt concrete pavement structures–-a thick pavement and a thin pavement–-were investigated. Pavement responses at selected locations in the pavement structures were computed by the finite element program using the measured tire–pavement contact stress data and compared with the results predicted by a multilayer program using the traditional uniform contact stress method. The computation results showed that the multilayer program and the traditional tire model tend to overestimate the horizontal tensile strains at the bottom of the asphalt concrete and underestimate the vertical compressive strains at the top of the subgrade. Prediction of effects of tire pressure on pavement performance shows that increased tire pressure results in increased pavement distress due to both cracking and rutting and that tire inflation pressure is also related to the shape of pavement ruts.

Mechanistic-Empirical Study of Effects of Truck Tire Pressure on Pavement: Measured Tire-Pavement Contact Stress Data

Truck tire pressure plays an important role in the tire-pavement interaction process. As a traditional approximation method in many pavement studies, tire-pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and simply equal to the tire pressure. However, recent studies have demonstrated that the tire-pavement contact stress is far from uniformly distributed. In this study, measured tire-pavement contact stress data were input to a finite element program to compute pavement immediate responses for three tire configurations: single tires, dual tires, and dual-tire tandem axles. Computed critical pavement responses were input to pavement distress transfer functions to analyze further the effects of tire inflation pressure on pavement performance. Two asphalt concrete pavement structures— a thick pavement and a thin pavement—were investigated. Pavement responses at selected locations in the pavement structures were computed by the finite element program using...

Mechanistic Comparison of Wide-Base Single versus Standard Dual Tire Configurations

Wide-base tires are gaining renewed interest in the U.S. trucking industry as tire and rim technology and design continue to improve. First introduced in the early 1980s and termed “super-singles,” new generation, wide-base tires have been developed to allow for lower inflation pressures and larger contact areas than their predecessors. Single tires are of interest to freight haulers because with fewer tires and lighter rims, cargo capacity can increase. Early theoretical and physical modeling studies of super-singles largely found them to be more damaging to highway pavement structures than standard dual tire configurations. However, in light of new tire advancements, the impact on pavement response and performance of the wide-base configuration should be reevaluated. In addition, the accuracy of theoretical models in predicting pavement response under the new wide-base tires should be evaluated because models are often used by agencies to determine single-tire weight limits and permitting. A conventional dual tire assembly (275/80R22.5) was evaluated versus a newly developed single wide-base tire (445/50R22.5) at the National Center for Asphalt Technology Test Track. Embedded asphalt strain gauges and earth pressure cells allowed for direct pavement response measurements and comparisons between the two configurations. In addition, theoretical modeling using layered elastic theory was used to evaluate both configurations. The pavement response measurements indicated no statistical difference between the two configurations. The theoretical model tended to overpredict the response under the wide-base configuration. Future studies should attempt to model the tire-pavement contact area precisely to improve accuracy under the wide-base tire.

Stresses in Concrete Pavement Slabs on Reissner’s Foundation Subjected to Floating Tandem Axles

Presented in this paper are stress and load factor charts for floating tandem axles acting on the interior of concrete pavement slabs resting on Reissner’s foundation. The floating tandem axle consists of dueled single axle followed by a single tired single axle or vice versa. The geometrical characteristics of the floating tandem axle were obtained from an axle load survey in Iraq. Based on the survey results, the floating tandem axle load frequency distribution histogram together with that for tire pressures were obtained. Circular tire-pavement contact areas between the tires of the floating tandem axle and the concrete pavement slab were assumed. The chart for the bending moment in concrete pavement slabs on Reissner’s foundation developed by Reddy and Pranesh[1] was used to determine the maximum bending moment due to interior loading by a floating tandem axle. The stress and load factor charts were developed for various slab thicknesses of 6, 8, 10, and 12 in. (15.24, 20.32, 25.40, and 30.48 cm). Using the developed stress charts, the maximum bending stress in the concrete pavement slab can be obtained directly for given floating tandem axle load and slab thickness.

STRESSES IN CONCRETE PAVEMENT SLABS ON REISSNER'S FOUNDATION SUBJECTED TOFLOATING TANDEM AXLES

Presented in this paper are stress and load factor charts for floating tandem axles acting on the interior of concrete pavement slabs resting on Reissner's foundation. The floating tandem axle consists of dueled single axle followed by a single tired single axle or vice versa. The geometrical characteristics of the floating tandem axle were obtained from an axle load survey in Iraq. Based on the survey results, the floating tandem axle load frequency distribution histogram together with that for tire pressures were obtained. Circular tire-pavement contact areas between the tires of the floating tandem axle and the concrete pavement slab were assumed. The chart for the bending moment in concrete pavement slabs on Reissner's foundation developed by Reddy and Pranesh[1] was used to determine the maximum bending moment due to interior loading by a floating tandem axle. The stress and load factor charts were developed for various slab thicknesses of 6, 8, 10, and 12 in. (15.24, 20.32, 25.40, and 30.48 cm). Using the developed stress charts, the maximum bending stress in the concrete pavement slab can be obtained directly for given floating tandem axle load and slab thickness.

Analytical Study of Effects of Truck Tire Pressure on Pavements with Measured Tire–Pavement Contact Stress Data

Truck tire inflation pressure plays an important role in the tire–pavement interaction process. As a conventional approximation method in many pavement studies, tire–pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and to be simply equal to the tire pressure. However, recent studies have demonstrated that the tire–pavement contact stress is far from uniformly distributed. Measured tire–pavement contact stress data were input into an elastic multilayer pavement analysis program to compute pavement immediate responses. Two asphalt concrete pavement structures, a thick pavement and a thin pavement, were investigated. Major pavement responses at locations in the pavement structures were computed with the measured tire–pavement contact stress data and were compared with the conventional method. The computation results showed that the conventional method tends to underestimate pavement responses at low tire pressures and to overestimate pavement responses at high tire pressures. A two-way analysis of variance model was used to compare the pavement responses to identify the effects of truck tire pressure on immediate pavement responses. Statistical analysis found that tire pressure was significantly related to tensile strains at the bottom of the asphalt concrete layer and stresses near the pavement surface for both the thick and thin pavement structures. However, tire pressure effects on vertical strain at the top of the subgrade were minor, especially in the thick pavement.

Quantification of the Joint Effect of Wheel Load and Tire Inflation Pressure on Pavement Response

Most pavement design and analysis procedures predict performance on the basis of expected pavement damage under traffic loads expected during design life. Some failure criteria are primarily dependent on wheel loads and almost independent of contact stresses. Others are primarily dependent on normal and shear stresses, not on load magnitude. Wheel load is used as a proxy for tire pressure to account for the effect of contact stresses indirectly. In most pavement design methods, tire–pavement contact stress is assumed to be equal to tire inflation pressure and to be uniformly distributed over a circular area. A methodology that explicitly accounts for the effect of tire inflation pressures and the corresponding contact stresses on pavement response is not available. In this research, pavement responses of typical pavement structures under the combined actions of variable wheel loads and tire pressures were evaluated. A multilayer, linear–elastic computer program was used to estimate three critical pavement responses: longitudinal and transverse tensile strains in asphalt and compressive strains in the subgrade. The differences of the strains estimated by the two models were statistically analyzed to quantify the effect of the assumption of uniform stress over a circular shape. The traditional model proved to be reliable to estimate compressive strains in the subgrade layer. The tensile strains in the asphalt layer under actual contact stress, however, were quite different from those under uniform constant stress. Contrary to initial expectation, for the general case, the assumption of uniform stresses is a conservative approach.

Quantification of the Joint Effect of Wheel Load and Tire Inflation Pressure on Pavement Response

Most pavement design and analysis procedures predict performance on the basis of expected pavement damage under traffic loads expected during design life. Some failure criteria are primarily dependent on wheel loads and almost independent of contact stresses. Others are primarily dependent on normal and shear stresses, not on load magnitude. Wheel load is used as a proxy for tire pressure to account for the effect of contact stresses indirectly. In most pavement design methods, tire-pavement contact stress is assumed to be equal to tire inflation pressure and to be uniformly distributed over a circular area. A methodology that explicitly accounts for the effect of tire inflation pressures and the corresponding contact stresses on pavement response is not available. In this research, pavement responses of typical pavement structures under the combined actions of variable wheel loads and tire pressures were evaluated. A multilayer, linear-elastic computer program was used to estimate three critical pavement responses: longitudinal and transverse tensile strains in asphalt and compressive strains in the subgrade. The differences of the strains estimated by the two models were statistically analyzed to quantify the effect of the assumption of uniform stress over a circular shape. The traditional model proved to be reliable to estimate compressive strains in the subgrade layer. The tensile strains in the asphalt layer under actual contact stress, however, were quite different from those under uniform constant stress. Contrary to initial expectation, for the general case, the assumption of uniform stresses is a conservative approach.

Analytical Study of Effects of Truck Tire Pressure on Pavements with Measured Tire-Pavement Contact Stress Data

Truck tire inflation pressure plays an important role in the tire-pavement interaction process. As a conventional approximation method in many pavement studies, tire-pavement contact stress is frequently assumed to be uniformly distributed over a circular contact area and to be simply equal to the tire pressure. However, recent studies have demonstrated that the tire-pavement contact stress is far from uniformly distributed. Measured tire-pavement contact stress data were input into an elastic multilayer pavement analysis program to compute pavement immediate responses. Two asphalt concrete pavement structures, a thick pavement and a thin pavement, were investigated. Major pavement responses at locations in the pavement structures were computed with the measured tire-pavement contact stress data and were compared with the conventional method. The computation results showed that the conventional method tends to underestimate pavement responses at low tire pressures and to overestimate pavement responses at...

Current Status and Variability of In-Service Truck Tire Pressures in Texas

Truck tire pressure is closely related to tire-pavement contact pressure and could be an easy index representing the tire-pavement contact pressure level. To characterize in-service truck tire pressures and truck configurations on Texas highways, a truck survey was conducted on major Texas trucking routes. The survey data demonstrate a significant increase in in-service truck tire pressures in the state of Texas. Analysis of the collected tire-pressure data showed that factors such as axle weight, tire temperature, geographic area, highway class, traveled distance, and axle type are related to the in-service tire-pressure values. In a survey study, a factorial experiment design and a stratified sampling design were used. Analysis of variance, analysis of covariance, and t-tests were used for comparisons of truck tire-pressure data. Laboratory experiments and linear regression were used to identify relationships between the parameters of tire pressure and tire temperature. The survey results for in-service truck tire pressures and the comparisons and analyses of factors differentiating truck tire pressures are presented.