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Numerical Investigation of the Effects of Shrinkage and Thermal Loading on the Behaviour of Misaligned Dowels in Jointed Concrete PavementLevy, Cyril January 2010 (has links)
Dowel bars in jointed plain concrete pavement (JPCP) have the important function of transferring wheel loads from one slab to the other, hence ensuring that the deflections on each side of the joint are kept almost equal. As well, the dowels should not impede the concrete pavement movements due to environmental effects (temperature and moisture). Dowel bar misalignment, attributed to deficient construction practice, is a major cause of joint distress or faulting by inhibiting the free movement of the slab at the joint. To prevent these issues, tolerance guidelines on misalignment levels are implemented by transportation agencies. Review of previous studies indicate that many researchers analysed the effects of dowel bar misalignment on pavement behaviour using a pull-out test, that is a forcebased opening of the joint. These approaches neglect that joints movements in the field are strain-governed by non-linear temperature and shrinkage actions, leading to combined axial
movements and curling of the slab.
In this study, the fundamental dowel bar behaviour under shrinkage and thermal loading
was determined through detailed 3D finite element modelling (3D-FEM). To that end, models of dowel jointed concrete slabs were developed and subjected to realistic non-linear profiles of shrinkage and thermal strains. Studies were carried out on a single-bar model, taking into account bar-concrete friction and plastic concrete behaviour. The parameters that were investigated included different configurations and levels of bar misalignment and different friction coefficients between the steel and the concrete, simulating the use of bond-breakers. To interpret the results from the numerical analysis, criteria for concrete damage were developed and used in parallel with measures of joint load transfer efficiency; these were obtained by examining the response of the slab under a Falling Weight Deflectometer (FWD) drop at the joint. The results were verified by comparing the outputs of a model consisting
of one half of a slab to published data.
The analysis of the models revealead that none of the models showed signs of significant damage after the application of shrinkage and two thermal cycles. Analyses with up to ten thermal cycles did not indicate progressive accumulation of damage, suggesting that for the chosen parameters there is no the concrete around the dowel bar will not fail. Models with bars placed higher in the slab and bars with angular misalignment exhibited more damage than the non-misaligned models without reaching the damage criteria used in this study. The models did not exhibit the amount of damage reported in the studies on dowel bar misalignment having used pull-out tests. It was found that no significant difference existed between uncoated and coated dowel bars models results with regards to concrete damage at the joint. However, a high coefficient of friction between the dowel and the concrete, simulating dowel bar corrosion, proved to be the most detrimental to joint integrity. All of the models performed very well with respect to joint load transfer efficiency, suggesting that
the plastic strains in the concrete around the dowel did not have a significant impact on joint performance for the realistic range of parameters investigated.
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Numerical Investigation of the Effects of Shrinkage and Thermal Loading on the Behaviour of Misaligned Dowels in Jointed Concrete PavementLevy, Cyril January 2010 (has links)
Dowel bars in jointed plain concrete pavement (JPCP) have the important function of transferring wheel loads from one slab to the other, hence ensuring that the deflections on each side of the joint are kept almost equal. As well, the dowels should not impede the concrete pavement movements due to environmental effects (temperature and moisture). Dowel bar misalignment, attributed to deficient construction practice, is a major cause of joint distress or faulting by inhibiting the free movement of the slab at the joint. To prevent these issues, tolerance guidelines on misalignment levels are implemented by transportation agencies. Review of previous studies indicate that many researchers analysed the effects of dowel bar misalignment on pavement behaviour using a pull-out test, that is a forcebased opening of the joint. These approaches neglect that joints movements in the field are strain-governed by non-linear temperature and shrinkage actions, leading to combined axial
movements and curling of the slab.
In this study, the fundamental dowel bar behaviour under shrinkage and thermal loading
was determined through detailed 3D finite element modelling (3D-FEM). To that end, models of dowel jointed concrete slabs were developed and subjected to realistic non-linear profiles of shrinkage and thermal strains. Studies were carried out on a single-bar model, taking into account bar-concrete friction and plastic concrete behaviour. The parameters that were investigated included different configurations and levels of bar misalignment and different friction coefficients between the steel and the concrete, simulating the use of bond-breakers. To interpret the results from the numerical analysis, criteria for concrete damage were developed and used in parallel with measures of joint load transfer efficiency; these were obtained by examining the response of the slab under a Falling Weight Deflectometer (FWD) drop at the joint. The results were verified by comparing the outputs of a model consisting
of one half of a slab to published data.
The analysis of the models revealead that none of the models showed signs of significant damage after the application of shrinkage and two thermal cycles. Analyses with up to ten thermal cycles did not indicate progressive accumulation of damage, suggesting that for the chosen parameters there is no the concrete around the dowel bar will not fail. Models with bars placed higher in the slab and bars with angular misalignment exhibited more damage than the non-misaligned models without reaching the damage criteria used in this study. The models did not exhibit the amount of damage reported in the studies on dowel bar misalignment having used pull-out tests. It was found that no significant difference existed between uncoated and coated dowel bars models results with regards to concrete damage at the joint. However, a high coefficient of friction between the dowel and the concrete, simulating dowel bar corrosion, proved to be the most detrimental to joint integrity. All of the models performed very well with respect to joint load transfer efficiency, suggesting that
the plastic strains in the concrete around the dowel did not have a significant impact on joint performance for the realistic range of parameters investigated.
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A GIS-enabled Multi-Year Pavement Rehabilitation Needs Analysis SystemGao, Bo 31 August 2004 (has links)
This dissertation presents the algorithm, methodology, modeling, and system development of a GIS-enabled multi-year pavement rehabilitation needs analysis system which can perform multi-year network-level pavement rehabilitation needs analysis subject to funding availability, minimum performance requirements, and balancing constraints. The system links network-level analysis results directly with project-level maintenance plans and, therefore, can generate not only network-level results but also detailed project-level rehabilitation plans, such as when to treat, where to treat and what treatment method to use.
The system first utilizes the current and historical project level pavement condition evaluation information stored in the central Oracle database to forecast future project performance ratings and distresses, to determine appropriate treatment methods and costs, and to calculate life-cycle cost effectiveness ratios for all the projects in the pavement network. Based on this information, a methodology was developed to perform various network-level analyses to determine multi-year funding requirements to meet various prescribed pavement performance requirements and to determine optimum pavement rehabilitation plans subject to funding availability and other requirements, such as balancing funding distribution or future pavement performance among Georgia Department of Transportation (GDOT) Engineering Districts or State Congressional Districts. The system integrates graphical information on GIS maps with information in the central Oracle database and the needs analysis results seamlessly so that engineers can perform interactive map-based multi-year what-if needs analysis directly on the maps using the framework and methodology presented in this dissertation. Several case studies using the actual historical pavement condition evaluation data from the GDOT are presented to illustrate the capabilities of the system. The dissertation concludes with a summary of major conclusions and recommendations for future research.
Besides linking network-level analysis results directly with project-level maintenance plans, the following major advantages of the system are also recognized: GIS technology is fully utilized in the system. The system is one of the first pavement needs analysis systems that allows an engineer to perform interactive map-based what-if scenario analyses on multi-year pavement needs analysis. The system allows the rehabilitation plans to balance pavement rehabilitation costs and performances among different political jurisdictions. The system can perform various types of analyses to develop multi-year rehabilitation plans subject to various budget and performance constraints together with the balancing constraints. Although the system was developed for GDOT, with slight modifications, the system can be used by engineers in other transportation agencies to perform the same analyses.
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Advancement of Erosion Testing, Modeling, and Design of Concrete Pavement Subbase LayersJung, Youn Su 2010 August 1900 (has links)
Concrete pavement systems have great capacity to provide long service lives; however, if
the subbase layer is improperly designed or mismanaged, service life would be
diminished significantly since the subbase layer performs many important roles in a
concrete pavement system. The erosion of material beneath a concrete slab is an
important performance-related factor that if applied to the selection of base materials can
enhance the overall design process for concrete pavement systems. However, erosion of
the subbase has not been included explicitly in analysis and design procedures since there
is not a well accepted laboratory test and related erosion model suitable for design.
Previous erosion test methods and erosion models are evaluated in terms of their
utility to characterize subbase materials for erosion resistance. With this information, a
new test configuration was devised that uses a Hamburg wheel-tracking device for
evaluating erodibility with respect to the degree of stabilization and base type. Test
devices, procedures, and results are explained and summarized for application in
mechanistic design processes. A proposed erosion model is calibrated by comparing
erosion to lab test results and LTPP field performance data. Subbase design guidelines
are provided with a decision flowchart and a design assistant spread sheet for the
economical and sustainable design of concrete pavement subbase layers by considering
many design factors that affect the performance of the subbase.
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Field monitoring and modeling of pavement response and service life consumption due to overweight truck trafficOh, Jeong-Ho 15 November 2004 (has links)
A number of pavement structures experience deterioration due to high traffic volume and growing weights. Recently, the Texas Legislatures passed bills allowing trucks of gross vehicle weight (GVW) up to 556 kN routinely to use a route in south Texas along the Mexican border. Thus, there is a need to model pavement responses due to various types of overweight truck traffic (OTT) by taking into account axle loads, configuration, and pavement layer material characterizations in order to provide a guideline to assess the existing pavement performance and expected service life. It is for this purpose that the nonlinear cross-anisotropic pavement analysis finite element program (NCPA) has been developed. Stress dependent and directionally different resilient modulus and Poisson's ratios are incorporated into the finite element formulation to model the pavement response. As a tool to assess the performance of the pavement, the procedure to calculate the overall rutting and the cracked area was included in the formulation
Intensive nondestructive testing has been performed to identify the existing pavement test section geometry and layer properties. In addition, a fiber optic based Weigh-in Motion (WIM) sensor was developed and tested. It is expected to be a promising device to monitor traffic by showing a reliable response. Sampled materials from the test section were tested to characterize their stress-dependent, cross-anisotropic and permanent deformation properties.
Constitutive models are verified by comparing the predicted displacements with field displacements measured with the Multi-Depth Deflectometer (MDD). The result was that the least error between predicted and measured displacements is generated by the nonlinear cross-anisotropic model. In addition, the cross-anisotropic characteristic of the asphalt concrete material is introduced and evaluated based on the relationship between the backcalculated static and dynamic modulus. This addition improves the accuracy of the assessment of pavement performance with respect to both rutting and fatigue cracking. Charts to evaluate the service life of the existing pavement subjected to OTTs are established in terms of the unit service life consumed due to the rutting and fatigue cracking with the various observed combinations of pavement geometry, traffic load, and material properties.
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Determination of aggregate physical properties and its effects on cross-anisotropic behavior of unbound aggregate materialsKim, Sung-Hee 01 November 2005 (has links)
Work done by several researchers reveals that unbound aggregate materials show nonlinear cross-anisotropic behavior. The incorporation of cross-anisotropic properties significantly improves the predictions of stress distribution by reducing tensile stresses computed within granular layers. Existing pavement analysis and design approaches, however, generally assume the pavement structure to be linear isotropic layered system. This assumption is motivated by the difficulties in determining cross-anisotropic resilient material properties from laboratory experiments and lack of pavement anisotropic analysis programs.
Recently, the International Center for Aggregates Research (ICAR) developed a methodology to characterize unbound aggregate layers by considering stress-sensitivity and nonlinear cross-anisotropy. The ICAR model requires nine coefficients to account for stress-sensitivity and anisotropy of vertical, horizontal, and shear moduli. Unfortunately, ICAR testing protocol is time-consuming and expensive to perform and certainly do not lend themselves to routine testing. Since it is important to be able to consider the stress-sensitive and anisotropic nature of unbound granular materials, a simple procedure was proposed by accounting for the effects of aggregate gradation and shape properties in predicting the cross-anisotropic modular ratio of unbound granular materials. Variable confining pressure type repeated load triaxial tests were performed on six aggregate sources with three different gradations and three different moisture contents. The experimental results were analyzed within the framework of nonlinear cross-anisotropic elastic model in order to determine the model coefficients. Image analysis techniques were utilized to measure aggregate shape properties. The gradation and shape properties were fitted using a cumulative distribution function and nonlinear regression analysis, which is capable of capturing the complete distribution of these properties. The experimental and analytical results indicate that the vertical resilient modulus is greater than the horizontal resilient modulus and that aggregate physical properties significantly affect the anisotropic resilient behavior.
Based on finite element analysis, the anisotropic resilient behavior has substantial effect on the critical pavement responses. Thus, it is extremely valuable to approximate the degree of cross-anisotropy in unbound aggregates and to use it as input in the pavement analysis programs to adequately model unbound aggregate bases for pavement design and analysis.
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An investigation into the predictive performance of pavement marking retroreflectivity measured under various conditions of continuous wettingPike, Adam Matthew 25 April 2007 (has links)
This thesis research investigated the predictive performance of pavement
marking retroreflectivity measured under various conditions of continuous wetting. The
researcher compared nighttime detection distance of pavement markings in simulated
rain conditions and the retroreflectivity of the same pavement markings in several
continuous wetting conditions. Correlation analyses quantified the predictive
performance of the resulting retroreflectivity values from the continuous wetting
conditions.
The researcher measured the retroreflectivity of 18 pavement marking samples
under 14 different conditions. The American Society for Testing and Materials (ASTM)
has three standards for measuring the retroreflectivity of pavement markings under:
dry (E-1710), recovery (E-2177), and continuous wetting conditions (E-2176). Using
three ASTM standard conditions resulted in three sets of retroreflectivity data, and
variations of the continuous wetting standard produced an additional 11 sets of
continuous wetting condition data.
The researcher also incorporated detection distance values measured for the
same 18 pavement marking samples under three different simulated rainfall conditions at night. The three conditions included: high (0.87 in/hr), medium (0.52 in/hr), and low
(0.28 in/hr) flow rates, these rates were to simulate typical rainfall rates in the state of
Texas.
The correlation analyses measures the linear relationship as well as the
logarithmic relationship between the detection distance and the retroreflectivity of the
pavement markings. A pavement markings' retroreflectivity is typically used as a
detection distance performance indicator, therefore a high degree of correlation between
retroreflectivity and detection distance would be desired. A high degree of correlation
would indicate that a measured retroreflectivity value of a pavement marking would
provide a good indication of the expected detection distance.
The researcher conducted analyses for several subgroups of the pavement
markings based on the markings type or characteristics. Dry, recovery, and all the
continuous wetting retroreflectivity data were correlated to the detection distances.
Correlation values found during this thesis research did not show a high degree of
correlation for most of the subgroups analyzed. This indicates that measured
retroreflectivity would not provide very good predictive performance of the pavement
markings detection distance in rainy conditions.
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Complementary imaging for pavement cracking measurementsZhao, Zuyun 03 February 2015 (has links)
Cracking is a major pavement distress that jeopardizes road serviceability and traffic safety. Automated pavement distress survey (APDS) systems have been developed using digital imaging technology to replace human surveys for more timely and accurate inspections. Most APDS systems require special lighting devices to illuminate pavements and prevent shadows of roadside objects that distort cracks in the image. Most of the artificial lighting devices are laser based, which are either hazardous to unprotected people, or require dedicated power supplies on the vehicle. This study is aimed to develop a new imaging system that can scan pavement surface at highway speed and determine the severity level of pavement cracking without using any artificial lighting. The new system consists of dual line-scan cameras that are installed side by side to scan the same pavement area as the vehicle moves. Cameras are controlled with different exposure settings so that both sunlit and shadowed areas can be visible in two separate images. The paired images contain complementary details useful for reconstructing an image in which the shadows are eliminated. This paper intends to presents (1) the design of the dual line-scan camera system for a high-speed pavement imaging system that does not require artificial lighting, (2) a new calibration method for line-scan cameras to rectify and register paired images, which does not need mechanical assistance for dynamical scan, (3) a customized image-fusion algorithm that merges the multi-exposure images into one shadow-free image for crack detection, and (4) the results of the field tests on a selected road over a long period. / text
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Implementation of a network-level pavement structural condition index based on falling weight deflectometer dataPeddibhotla, Sruthi Sree Sravya 14 February 2011 (has links)
The Texas Department of Transportation (TxDOT) uses the Pavement Management Information Systems (PMIS) to store and analyze pavement data, and to summarize information needed to support pavement-related decisions. The information on overall condition of the pavement is stored in PMIS, measured with various scores based on visual distress and ride quality surveys. However, a direct measure of the pavement structural condition is currently not in use. A network-level index that can distinguish pavements that require Preventive Maintenance (PM) from those that require Rehabilitation (Rhb) is required, because, it is not cost-effective to apply PM treatments to pavements that are structurally inadequate. The necessity to use an index to improve pavement treatment selection process, especially under financial constraints has motivated this research. The objective of this research is to validate the pavement Structural Condition Index (SCI) developed under a previous Research Project 0-4322, and to develop guidelines for implementing the SCI at the network level. / text
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Statistical analysis of TxCAP and its subsystemsQazi, Abdus Shakur 29 September 2011 (has links)
The Texas Department of Transportation (TxDOT) uses the Texas Condition Assessment Program (TxCAP) to measure and compare the overall road maintenance conditions among its 25 districts. TxCAP combines data from three existing subsystems: the Pavement Management Information System (PMIS), which scores the condition of pavement; the Texas Maintenance Assessment Program (TxMAP), which evaluates roadside conditions; and the Texas Traffic Assessment Program (TxTAP), which evaluates the condition of signs, work zones, railroad crossings, and other traffic elements to get an overall picture of the condition of state roads. As a result, TxCAP provides a more comprehensive assessment of the interstate and non-interstate highways. However, the scores for each of the subsystems are based on data of different sample sizes, accuracy, and levels of variations, making it difficult to decide if the difference between two TxCAP score is a true difference or measurement error. Therefore, whether the use of TxCAP is an effective and consistent means to measure the TxDOT roadway maintenance conditions raises concerns and needs to be evaluated. In order to achieve this objective, statistical analyses of the system were conducted in two ways: 1) to determine whether sufficient samples are collected for each of the subsystems, and 2) to determine if the scores are statistically different from each other. A case study was conducted with a dataset covering the whole state from 2008 to 2010. The case study results show that the difference in scores between two districts are statistically significant for some of the districts and insignificant for some other districts. It is therefore recommended that TxDOT either compare the 25 districts by groups/tiers or increase the sample size of the data being collected to compare the districts as individual ones. / text
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