Contact-Element Model for Dynamic Analysis of Jointed Concrete Pavements

Essential modern transportation systems together with the high demand for sustainable pavements under applied vehicular loading have led to a great deal of research worldwide of concrete pavements. Despite progressive knowledge of concrete pavement behaviour under applied loads, concrete pavements are still subject to deterioration due to crack initiation and propagation, indicating the need for further research. Cracks can be related to fatigue of concrete or erosion of materials in sub-layers. Transverse joints in concrete pavements are the locations where most pavement distress appears, leading to deterioration of the riding quality and featuring high maintenance cost. The state of stresses in the concrete surrounding dowel bars, in dowel jointed concrete pavements, are a major factor that contribute to transverse joint distress. A three-dimensional (3D) finite element model is developed in this study for analysing a dowel-jointed concrete pavement. The effects of different pavement and joint related parameters on the load transfer characteristics of a joint have been evaluated using the 3D finite element model. The numerical results from FE modelling are validated with classical analytical solutions of shear and moment along the dowel. Five loading cases are applied in the model to replicate realistic vehicular loadings approaching and leaving the joint. Group action of the dowel bar system has also been examined.

With the further adoption of mechanistic-empirical design methods in the pavement industry, the calculation of critical responses and cumulative damage for a variety of parameters will be imperative. Traditionally, the critical tensile stress developed by loads at the midslab edge has been used as a mechanistic parameter to determine the required thickness in jointed concrete pavements. However, the inclusion of both temperature and shrinkage gradients in concrete pavement analysis can drastically alter the critical stress location and subsequent distress type that predicts pavement performance. Longitudinal and corner cracking have been found in California to be distresses as significant as transverse cracking. Most of the longitudinal and corner cracking can be explained by excessive differential drying shrinkage. Using finite-element analysis, this study compared the critical tensile stress near the transverse joint with the critical tensile stress at the midslab edge (relative reference stress) for California-type jointed plain concrete pavements. The analysis of the data showed that transverse joint loads were more significant in critical stress calculations for a considerable number of input parameters. These loads at the transverse joint can manifest themselves as top-down or bottom-up longitudinal, transverse, or corner fatigue cracks unlike the bottom-up transverse cracks traditionally predicted by midslab edge loads. The likelihood of critical slab stresses near the transverse joint was considerably increased with the use of negative temperature gradients and extended lane widths.

The interface bonding condition between asphalt pavement layers is always imperfect because of the differing material properties of different layers and the limitation of construction techniques. Therefore, designing asphalt pavement by considering the interface to be completely continuous is not precise. The viscoelastic character of the asphalt layer contributes significantly to the performance of asphalt pavement. To explore the influence of the imperfect interface on the viscoelastic dynamic response of asphalt pavement, the Hankel–Laplace transformation was applied to convert the partial differential equations to ordinary differential equations and a transfer matrix was introduced to describe the behavior of the imperfect interface. Based on the boundary condition and integral inverse transformation technique, an analytical solution for the displacement, stress, and strain of the pavement can be obtained. By considering the variation in the interface condition and the viscoelastic characteristics of the asphalt layer, the dynamic response of the pavement was calculated based on a practical example. The results show that the interface condition between the asphalt layer and the base course has a marked influence on the viscoelastic dynamic response of the pavement and that enhancing the strength of this interface can reduce the deflection of the pavement. The series elastic component in the modified Burgers model is another significant factor that affects the calculation results of the pavement dynamic response.

This paper presents an analysis of the potential impact of misaligned dowel bars on concrete pavement joint performance. The performance and efficiency of a concrete pavement joint is assessed through the ability of the joint to expand and contract under temperature variations. With the finite difference method, the pullout force and stress distribution resulting from various dowel bar misalignment combinations are compared to propose an acceptable misalignment value. It was found that the stress within the concrete is acceptable for dowel bar misalignments of 20 mm, and cracking is expected to occur if a dowel bar is misaligned by more than 25 mm.

A solution algorithm based on three-dimensional (3D) finite-element analysis is presented to study the dynamic response of concrete pavements subjected to moving loads. The pavement is discretized by 20-node isoparametric brick elements. The supporting soil medium is idealized by the elastic continuum model. Kelvin elements are attached to the transmitting boundary separating the near field and far field of the infinite soil medium in the vertical and longitudinal directions. Three-dimensional, 16-node infinite elements are attached to the transmitting boundary in the longitudinal direction to simulate the infinite soil medium in vehicle traverse direction. The moving vehicle is modeled by a mass supported by a linear spring and dashpot assembly simulating the vehicle suspension system. The vehicle-pavement interaction force is modeled with a Dirac-delta function. The dynamic equilibrium equation is solved by applying the Newmark-Beta integration scheme. The effects of vehicle-pavement interaction, pavement thickness, and soil parameters on the dynamic response of pavement are investigated by conducting a parametric study. It has been observed that the dynamic interaction between the moving load and the pavement has a significant effect on pavement response.

Effective load transfer is a key design element for jointed plain concrete pavement and has a significant impact on long-term pavement performance. To facilitate load transfer and to allow expansion and contraction of the joints, dowel bars should be placed parallel to the vertical and horizontal planes of the pavement. In the past, it was difficult to verify the alignment of dowel bars within a concrete pavement. Recently, the Ontario Ministry of Transportation was given the opportunity to verify dowel bar alignment with an innovative non-destructive technique known as magnetic imaging tomography (MIT). The MIT scan was found to be a quick and accurate method of measuring dowel bar alignment across a transverse joint, allowing real-time, non-destructive assessment of the dowel bar alignment at joints throughout a concrete paving contract. In Ontario, MIT scan data collection and analysis during concrete paving led to process and equipment improvements. The MIT scan was rapidly adopted both as a quality control tool for the contractor and a quality assurance tool for the ministry. Based on data collected over several paving seasons, changes were made to ministry specifications and dowel bar tolerances. The revised dowel bar tolerances for Ontario pavements are presented in this paper.

A finite element algorithm is presented to evaluate the dynamic response of pavements including aircraft‐guideway‐foundation interaction. The pavement‐foundation system is modeled by a series of thick plate elements supported by discrete springs and dashpots at the nodal points representing the viscoelastic foundation. The moving aircraft loads are represented by masses each supported by a spring and dashpot suspension system and having a specified horizontal velocity and acceleration. The accuracy of the algorithm is verified by comparing the finite element solution with available analytical results. A parametric study is conducted to determine the effects of various parameters on the dynamic response of pavements to moving loads.

This paper provides a critical review of the ‘trigger’ to reseal transverse contraction joints in plain concrete pavements given that sealant distress is not uniform along the joint length, traffic management costs are a significant cost, minimising traffic disruption at high volume sites is important, and maintenance funding being limited and directed to ‘safety first’ maintenance activities. In NSW, Australia, all contraction joints are sealed with a highway grade silicone sealant. When sealed with the reservoir clean and dry, the joint sealant should remain in place without cracking for at least 15 years. However, joints sealed incorrectly typically result in early age adhesion failure. Poor joint cleanliness or sealing too early, has been shown to result in seal distress under the wheel paths within the first 2 years. It is also common for the sealant to become distressed in the slow (outer) lane while the sealant is in satisfactory condition in the fast (inner) lane. Recommendations for an interim empirical procedure are provided to assist asset managers evaluate the ‘triggers’ for resealing existing joints. The recommendations are based on the age of the pavement and incorporate: (a) Simplified definition for sealant defect, (b) Implementation of a random inspection technique to determine the extent of seal distress and more informed decision making on contraction joints to be resealed, and (c) The extent of resealing in a transverse joint over multiple lanes.

During the curing of Portland cement concrete (PCC) pavements, temperature and moisture gradients in the concrete cause pavement slabs to deform from their initial as-placed shape. Daily and seasonal environmental cycling can then cause the slabs to expand and contract horizontally with changes in average temperature and moisture conditions, and curl and warp vertically as temperature and moisture gradients change through the slab depth. This article reports on a study that evaluated slab shape under controlled environmental conditions. In the study, two 3.66 m (12 ft) wide, by 13.72 m (45 ft) long, by 254 mm (10 in) thick concrete pavements were constructed in the Ohio Accelerated Pavement Loading Facility (APLF). Transverse contraction joints were placed at 4.57 m (15 ft) intervals to create three contiguous 4.57 m (15 ft) long slabs in each pavement. Dowel bars were added to the joints in one pavement, and the other pavement was left undoweled. Results demonstrated large upward vertical deformations along the slab edges early in the curing cycle, and these deformations continued to increase throughout the duration of the tests. The slightly smaller vertical movements observed in the doweled pavement were attributed to the presence of the dowel bars. The authors conclude that by restraining joint movement, dowel bars transferred load to adjacent slabs and reduced slab deformation. They note that forces in the dowel bars were smaller than expected from reports on previous investigations, particularly during the curing process. When modeling PCC pavements, loss of support from the base should be considered as dead and live load stresses are generated in cantilevered slabs.

The design and performance of concrete pavement test sections constructed in Wisconsin in the summer of 1997 to validate the constructability and potential cost-effectiveness of alternative concrete pavement designs incorporating variable dowel strategies and slab thicknesses are described. To reduce the number of dowel bars across the transverse joints and remain consistent with dowel bar installation equipment currently used within the state, four alternative dowel patterns were examined. Test sections were constructed with alternative dowel materials including fiber-reinforced polymer (FRP) composite dowels, solid stainless steel dowels, and hollow core mortar-filled stainless steel dowels as well as a variable slab thickness. Postconstruction monitoring including deflection testing, joint distress surveys, and ride quality surveys have been done. Observed joint distress including minor spalling, chipping, and fraying is mainly due to joint saw cut operations. No transverse joint faulting or slab cracking has been observed. Deflection testing to date indicated general uniformity of foundation support in all test sections. Deflection testing has also been done across transverse joints to quantify deflection load transfer efficiency. Joint tests in the fall of 1997 and 1998 indicated reduced load transfer efficiencies in all test sections compared with control sections, most notably in the FRP composite dowel test sections and the placement alternative with three dowels in each wheelpath. Ride quality surveys indicated general uniformity among sections.

Past research on dowel bar placement has evaluated dowel bar misalignment relative to the saw cut at the top of the pavement. Determining misalignment measurements relative to the saw cut at the top of the pavement assumes that the crack propagates vertically downward immediately below the saw cut joint. This assumption is flawed although it is current practiced by the industry. Present detection methods cannot accurately determine the point at which the crack crosses the dowel bar. This study recognizes that there is not a technique to determine the path of the crack to measure the true misalignment but offers an alternative by dictating the crack path with cracking initiators attached to the dowel bars. Previous research has indicated that cracking initiators secured to the base of the pavement are ineffective or have little benefit due to the stress profile in the pavement slab. This study presents the results of work performed in dictating the path of a crack by attaching the crack initiator to the dowel bars. The results include utilizing different shape and size initiators. The work performed to date on crack initiation and the benefits attributed to utilization of crack initiator, including the ability to determine the true amount of misalignment are presented.

This work reviews models and methods for determining the dynamic response of pavements to moving vehicle loads in the framework of continuum-based three dimensional models and linear theories. This review emphasizes the most representative models and methods of analysis in the existing literature and illustrates all of them by numerical examples. Thus, 13 such examples are presented here in some detail. Both flexible and rigid (concrete) pavement models involving simple and elaborate cases with respect to geometry and material behavior are considered. Thus, homogeneous or layered half-spaces with isotropic or cross-anisotropic and elastic, viscoelastic or poroelastic properties are considered. The vehicles are modeled as simple point or distributed loads or discrete spring-mass-dashpot system moving with constant or variable velocity. The dynamic response of the above pavement-vehicle systems is obtained by analytical/numerical or purely numerical methods of solution. Analytical/numerical methods have mainly to do with Fourier transforms or complex Fourier series with respect to both space and time. Purely numerical methods involve the finite element method (FEM) and the boundary element method (BEM) working in time or frequency domain. Critical discussions on the advantages and disadvantages of the various pavement-vehicle models and their methods of analysis are provided and the effects of the main parameters on the pavement response are determined through parametric studies and presented in the examples. Finally, conclusions are provided and suggestions for future research are made. • A review on models and methods for dynamic analysis of road pavements under moving vehicle loads is presented. • Flexible and rigid pavements are considered under 3D continuum-based models with linear theories and conditions. • Representative examples serve to illustrate models and methods of analysis.

This paper presents the performance of three rehabilitation methods on six highways to restore the condition of concrete pavement: (1) polyurethane foam injection (PFI), (2) dowel bar retrofit (DBR), and (3) full depth repair (FDR). PFI was able to raise the slabs to the target levels; however, it was not able to maintain the slabs at the target levels and thus prevent slabs from further settlement. In addition, new cracks have been observed in some slabs and it was believed that PFI might have created uneven supports that allowed the truck traffic to shatter the slabs. Long-term benefits of DBR were demonstrated on a project with 10 years of traffic, where asphalt overlay was placed. Only minimum reflective cracks were observed on the DBR sections as compared to severe reflective cracks on sections without DBR. In another project, DBR effectively restored the ride quality that reduced the International Roughness Index (IRI) from 2.83 m/km to 1.26 m/km. The poor ride of this pavement section before DBR was due mainly to severe faulting. This illustrates that dowel bars provided excellent load transfer at transverse contraction joints, which minimized the potential for faulting. FDR has been used to repair localized pavement distresses. However, subsidence of slabs and cracks reappeared on the slabs that received FDR, due partly to the inadequate base support. Currently, there are no objective test methods and criteria for base preparation in the FDR specifications. To improve the effectiveness of FDR, current FDR specifications need to be revised.

Pavement performance evaluation and fatigue life determination is an important part of pavement design and analysis. Laboratory testing in itself could not totally predict these parameters as it is neither possible to simulate the traffic conditions, nor costly pavement prototypes could be constructed because of lack of space and specific equipment to evaluate the prototype performance. In this study a pavement prototype was constructed, and subsequently validated for a FEM model designed on ABAQUS. Self-compacting concrete (SCC) was used as it is easier to work upon during initial construction as well retrofitting. Pavement performance was studied in terms of deflections upon loading as well as fatigue life when normal pavement quality concrete pavement was retrofitted with similar concrete, and SCC respectively. It was found that after retrofitting with SCC also, the pavement performs better as the deflections were comparable in both situations, whereas the fatigue life of the pavement improved by a magnitude of nearly 20%. Improvement in load transfer through dowel bars helped the retrofitted pavement to take a greater number of load repetitions.

Automated joint faulting measurement based on full-lane 3D pavement surface data