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6 None of the identified spalling models could be used for [203 and 229 mm], 10 sections with thickness between analyzing the effects of dowel misalignment on joint 9 and 10 in. [229 and 254 mm], 20 sections with thickness spalling. between 10 and 11 in. [254 and 279 mm], and 20 sections with thickness 11 in. [279 mm]. Based on these evaluations, the MEPDG faulting and crack- Dowel size: 16 sections with 1.25-in. [32 mm] diameter ing models were selected for modification in this study and dowels, 42 sections with 1.5-in. [38 mm] diameter dowels, the MEPDG International Roughness Index (IRI) model was and 2 sections with dowels of other diameters (1 and 1.125 in. adapted for roughness prediction. [25 and 29 mm]). Dowel installation procedure: 35 sections were constructed using basket assemblies, 23 sections using DBI, and 2 sections 2.3 Research Approach were retrofitted. The following section describes the approach used in con- Construction year: 4 sections were constructed before 1991, ducting field and laboratory tests, analytical modeling, and 22 sections between 1991 and 1995, 10 sections between developing performance predication models for JPCP with 1995 and 2000, 20 sections between 2000 and 2006, and misaligned dowels. 4 sections in 2007. Average daily traffic (ADT): 16 sections had ADT 15000, 12 sections had ADT between 15000 and 30000, 19 sections 2.3.1 Field Testing had ADT between 30000 and 60000, 12 sections had ADT The field testing included (a) evaluation of typical dowel 60000, and 1 section (on MnROAD) had 100,000 passes of alignments observed across the United States for a variety of 80 kip (35.6 kN) truck. construction projects and (b) identification of short-term and long-term effects of dowel misalignment on pavement 2.3.1.2 Data Collection performance. Every joint in each pavement section was tested using MIT Scan-2, and MagnoProof (MIT Scan-2 PC software) was 2.3.1.1 Alignment and Performance Database used to quantify dowel alignment and position in the pave- A database of the dowel alignment and pavement perform- ment section. ance was assembled from the evaluation of 37 pavement sec- In addition to the dowel alignment and position data, fault- tions and information on 23 additional pavement sections ing of each transverse joint was measured using a faultmeter reported in other studies (Yu, 2005). These 60 pavement reading to the nearest 0.01 in. (0.25 mm). Readings were taken sections are located in Arizona, California, Colorado, Georgia, in the outer wheel path (approximately 18 in. [450 mm] from Indiana, Illinois, Kansas, Michigan, Minnesota, Missouri, the edge of the lane) and at the slab corner. Thus, for a 500-ft. Nevada, North Carolina, Ohio, South Dakota, Virginia, (150-m) section with 15-ft. (4.6-m) joint spacing, over 30 Washington, and Wisconsin. faulting measurements were made. A complete distress survey The candidate sections for field data collection were iden- of each pavement section also was conducted in accordance tified with assistance from state DOTs. Another source of with the LTPP Distress Identification Manual (Miller and projects for field evaluation was the Long Term Pavement Bellinger, 2003); the extent and severity of cracking, spalling, Performance (LTPP) database, particularly the Seasonal Mon- corner breaks, and so on were noted. At each transverse joint, itoring Program (SMP) sections because they included infor- the overall extent of joint deterioration was noted and the mation on joint opening and historical time series on distress, severity was rated as None, Low, Medium, or High. The faulting, LTE, etc. Seventeen of the 37 pavement sections condition of the joint seal (if present) also was noted. Digital surveyed in this study are LTPP test sections. Appendix B lists photographs were taken to document the overall condition of all pavement sections, summarizes their design features, and each test section and typical distresses (if any), as well as the describes the testing operations performed on each. These site conditions. On some sections, joint LTE was measured sections represent broad ranges of design, construction, climate using the Falling Weight Deflectometer (FWD). and traffic variables: 2.3.2 Laboratory Testing Climatic region: 8 sections in dry-freeze, 24 sections in dry-nonfreeze, 22 sections in wet-freeze, 6 sections in Laboratory testing was conducted on pavement slabs in wet-nonfreeze. a controlled environment to determine the effects of dowel Pavement thickness: 5 sections with thickness 8 in. misalignment. Performance parameters such as maximum [203 mm], 5 sections with thickness between 8 and 9 in. required pullout force, dowel shear stiffness, and ultimate

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7 dowel shear capacity were measured. The standard pullout test was modified to eliminate the influence of beam rotation. Also, shear pull tests were conducted to address the effect of Dowel extension misalignment on shear performance. 2.3.2.1 Laboratory Setup Dowel inserter Each specimen consisted of a 4-ft. wide [1.2 m], 8-in. thick Tapped end of [203 mm], and 18-in. [457 mm] tall concrete beam containing the dowel four 1.25- or 1.5-in. [32 or 38 mm] diameter dowels placed 12 in. [305 mm] apart, with the end dowels 6 in. [152 mm] away from the edge (Figure 2.3). Test specimen dimensions were selected with consideration to the capabilities of the available test apparatus and the planned finite element modeling. Figure 2.4. Dowel extension and alignment jig. Beam thickness was based on a general design of a thin (8-in. [200-mm] thick), doweled PCC pavement. The width was chosen as the most efficient width for casting and testing offset to provide the desired misalignment (see Figure 2.4). the dowels using the available testing apparatus and the height The top end of each dowel was tapped to allow a dowel exten- was selected to ensure that the test beam adequately represents sion to be screwed into place. The extended dowel was inserted a "long" PCC slab (i.e., the specimen has sufficient length in through the jig holes and set at the proper embedment length the direction of dowel embedment such that boundary con- and angle. After the concrete had been placed and cured suf- ditions do not significantly influence test results). The finite ficiently, the dowel extension and jig were removed. element simulation of the modified pullout test indicated that The mold was stripped from the specimen after the con- increasing the beam height beyond 18 in. [457 mm] would not crete was cured sufficiently (a minimum of 24 hours) to avoid provide any advantage but would increase specimen weights damage. Each beam was then cured under water for 6 days and make it difficult to handle. before testing. One ungreased 6-in. [153-mm] dowel was The 1.25- and 1.5-in. [33- and 38-mm] dowel diameters were included and tested in each beam to provide a reference between chosen because they are commonly used in the United States. beams. A compressive strength test was conducted 7 days after The distance between the dowels was selected to ensure that beam casting. (1) the specimen clamps could be placed on the beam at The MinneALF structure was modified to accommodate the sufficient distances from each dowel being tested to avoid modified pullout and shear pull tests (Khazanovich et al., 2005). influencing the test results and (2) the damage of the beam These modifications included adjustment of the actuator after a pullout test on one dowel would not affect the adjacent positions and installation of the beam clamping mechanism. dowels. To ensure precision in installing the dowels with the intended 2.3.2.2 Test Procedure misalignment, a dowel jig was fabricated and a procedure was used for setting dowels with precisely the desired type and The dowel pullout testing was conducted after the test beams amount of misalignment. Each jig featured two holes that were had been water-cured for 7 days. Because concrete pavement can experience contraction and shrinkage within several hours after concrete setting, the 7-day curing time was selected to ensure uniformity of the test beams. Dowels with various levels of misalignments were tested as follows: 1. Each dowel was tested individually by pulling it vertically with respect to the concrete beam, along the ideal axial direction of a properly aligned dowel in a displacement- controlled mode at a rate of 0.003 in./sec (0.076 mm/sec) until the dowel had translated (pulled out) 0.25 in. (6 mm) relative to the concrete. Pullout force and displacement were recorded continuously. 2. A post-test examination was conducted to evaluate the con- Figure 2.3. Test specimen. crete surrounding the dowels (visible damage was recorded).

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8 After the pullout test was completed, the beam was rotated 2.3.2.3 Testing Factorial 90 degrees so that it was lying on its side (Figure 2.5). The The levels of misalignment used in the tests were selected beam then was clamped to the test stand and a shear load based on a review of previous misalignment investigations, was applied to selected dowels in a direction perpendicular which showed that dowel rotational misalignments of up to the plane of the slab surface. The dowel was pulled in a to 1 in. [25 mm] cause only small changes in distress and displacement-controlled mode until failure. resistance to joint opening (Tayabji, 1986; Prabhu et al., Dowels with various levels of misalignments were tested as 2006). Tests of dowels with up to 4 inches [102 mm] in follows: vertical tilt showed no significant differences in behavior 1. Each dowel was tested individually by pulling it vertically for the various levels of misalignment (Tayabji, 1986). Other with respect to the concrete beam, in a displacement- tests found no distresses for levels of skew and tilt of up controlled mode until the concrete surrounding the to 1 in. [25 mm] for vertical and horizontal misalignment dowel failed. During the testing, the shear pull force and and up to 3/4 in. [19 mm] for combined tilt and skew (Prabhu displacements of the dowel and concrete were recorded et al., 2006). continuously. In this study, tests were conducted on dowels with rotation 2. After testing each beam, an examination was conducted. ranging from 0 in. (i.e., properly aligned) to 4 in. per 18 in. The concrete surrounding the dowels was evaluated and [102 mm per 457 mm], embedment length ranging from 2 to the failure mode was recorded. 9 in. [51 to 229 mm], and concrete cover ranging from 1.25 to 3.375 in. [32 to 86 mm]. Because a typical dowel is 18 in. The effect of misalignment also was evaluated in repeated [229 mm] long, all dowel rotations are expressed as the ver- shear load tests with the following parameters: tical or horizontal displacement of one end of the dowel per 18 inches [229 mm] in length. Magnitude of loading: 3 kips [13.3 kN]. Pullout tests were conducted on specimens, each containing Load frequency: 2 Hz. four dowels with various types and levels of misalignment. Rest period: 0.5 seconds. To reduce the residual effect After the test, the two dowels on the outside of the beam were ("bouncing"), a static "seating" load of 500 lb [2.2 kN] was tested in shear or repeated shear (Appendix C presents the present between loading cycles. dowel alignments for each dowel tested in this study). Measurement frequency: every 0.1 seconds. Shear testing of the first two beams revealed difficulties in Number of load cycles: at least 10,000. testing four dowels within a single test beam due to the occur- rence of horizontal cracks. It was concluded that only the The laboratory process and setup for the repeated load test outside dowels could be tested to measure the ultimate shear was the same as that used for the static test, except that a repeated load capacity of a given dowel because testing of the interior 3-kip [13.3 kN] load was applied for at least 10,000 cycles. In dowels would result in horizontal cracks that would influence this manner, the effect of a one-time load to failure on strength the shear pull test results of adjacent dowels. Therefore, all of and stiffness could be related to the effect of a repeated load the dowels were tested in pullout but only the outside dowels fatigue test. were tested in shear, as noted in Figure 2.6. Figure 2.5. Setup for vertical shear test (also for repeated shear testing).

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9 Pull, shear Pull Pull Pull, shear Shear Pull Direction Concrete beam Figure 2.6. Tests conducted on individual dowels in a beam. LVDT 1 LVDT 2 LVDT 3 LVDT 4 Clamping Angles 2.3.2.4 Results Interpretation Figure 2.8. Locations of displacement measurements. Modified Pullout Tests. During pullout testing, the pullout force and displacements were recorded continuously. Figure 2.7 shows an example of the two types of curves recorded. Shear-Pull Tests. Figure 2.8 shows the locations at which Throughout the pullout testing, a majority of the dowels vertical displacement measurements were recorded. The first showed a monotonically increasing force-displacement curve linear variable differential transformer (LVDT1) measures the (i.e., the pullout force increased with dowel displacement) and displacement of the metal angle above the dowel, giving a others showed discontinuous force-displacement curves, simi- measure of absolute dowel displacement. LVDT2 measures the lar to those shown in Figure 2.7. The behavior illustrated by the displacement at the edge of the concrete beam closest to the properly aligned curves is characterized as "static-slip" because dowel, LVDT3 measures the beam displacement 2 in.[51 mm] it appears that the dowel "slips" slightly each time enough from the edge, and LVDT4 measures the beam displacement force is generated to exceed the static friction conditions. 4 in. [102 mm] from the edge. All four LVDTs are located in In these tests, maximum pullout force for a dowel with a the vertical plane of the dowel (i.e., directly above the dowel). given combination of misalignments was increased and then The shear-pull force and displacements of the dowel at the used to evaluate the effects of dowel misalignment on dowel joint face (LVDT1) and at the three locations on the beam resistance to joint opening and joint lockup. (LVDTs 2 through 4) were recorded continuously during It should be noted that the measured pullout forces in this study were higher than the pullout forces reported from foren- testing. Figure 2.9 shows an example of the recorded displace- sic studies in which the doweled joints were extracted from ments and shear force for a 1.5-in. [38-mm] diameter dowel pavements and tested in the lab. The difference is probably that was vertically tilted by 2 in. per 18 in. [51 mm per 457 mm] because the laboratory-prepared specimens were cured for of dowel length. 7 days before testing whereas the in situ dowels were subjected to joint movements at a much earlier age. 8000 8000 6000 7000 Shear Force, lbs. monotonically 6000 increasing Pullout Force, lbs. 4000 5000 dowel displacement (LVDT1) static slip 4000 edge displacement (LVDT2) 3000 2000 2 in. displacement (LVDT3) 2000 4 in. displacement (LVDT4) 1000 0 0 0 0.05 0.1 0.15 0.2 0 0.05 0.1 0.15 0.2 0.25 Relative Dowel Displacement, in. Dowel Displacement with Respect to the Concrete, in. Figure 2.9. Force versus displacement for a 2 in. Figure 2.7. Examples of the typical pullout test results. vertically tilted dowel.

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10 To conduct analyses of the effects of dowel misalignment 8000 on the stiffness of the dowel-concrete interaction, the relative 7000 vertical displacement of the dowel end with respect to the 6000 surrounding concrete was estimated by subtracting the cal- Shear Force, lbs. 5000 culated dowel displacement due to the rigid body rotation of dowel displacement (LVDT1) the beam from the actual dowel displacement. The calculated 4000 dowel calculated displacement dowel displacement was determined from the displacements of 3000 edge displacement(LVDT2) LVDT2 and LVDT4 (Figure 2.8) and the specimen geometry. 2000 2 in. calculated displacement These displacements were used to calculate the slope of the 2 in. displacement(LVDT3) 1000 rigid body motion of the beam, rb as follows: 4 in. displacement (LVDT4) 0 2 - 4 0 0.05 0.1 0.15 0.2 rb = (1) Relative Dowel Displacement, in. l24 Figure 2.11. Measured and calculated force versus where displacement for a 2 in. vertically tilted dowel. l24 = the distance between LVDT2 and LVDT4; 2 = the vertical displacement at the edge of the beam (measured by LVDT2); and This plot confirms appropriateness of the rigid body assump- 4 = the vertical displacement 4 inches [102 mm] from the tion for the rotation of the concrete beam. edge (measured by LVDT4). Figure 2.11 shows the calculated values for LVDT1 and LVDT3 for the example illustrated in Figure 2.9. The plot The slope of the rigid body could then be used to calculate the shows that, while the beam surface displacements can be position of the dowel, assuming rigid body motion (i.e., that the described as rigid body motion (i.e., the measured and calcu- beam rotates under load without bending) as follows: lated data points at 2 in. [51 mm] from the joint face are sim- ilar), the dowel exhibits additional displacements with respect calc = 4 + rb l14 (2) to the concrete beam surface. The relative dowel displacement can be computed as: where l14 = the distance between LVDT1 and LVDT4; and rel = meas - calc (3) calc = calculated dowel displacement assuming rigid body motion. where rel = the dowel displacement due to the compression of the To check the accuracy of the rigid body motion calculation, concrete around dowel; the displacements at LVDT3 were calculated similarly and calc = the calculated rigid body displacement; and compared to the actual LVDT3 measurements. Figure 2.10 meas = the dowel displacement measured by LVDT1. shows a typical example of the calculated versus measured dis- placements at the 2 in. [51 mm] location for the same dowel. Figure 2.12 shows a plot of applied shear force versus relative dowel displacement. The relative dowel displacement was used 0.06 Calculated Displacement (2 in. from edge), in. 12000 Failure of Concrete 0.05 Surrounding the Dowel 9 in. embedment 0.04 8000 Shear Force, lbs. 0.03 4000 0.02 0.01 0 0 0 0.01 0.02 0.03 0.04 0.05 0.06 0 0.01 0.02 0.03 0.04 0.05 0.06 Relative Dowel Displacement, in. Measured Displacement (2 in. from edge), in. Figure 2.12. Example of shear force versus relative Figure 2.10. Verification of the rigid body slope. displacement.

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11 to estimate the degree of deformation of the concrete during and vertical clamping mechanisms with a temperature-sensitive testing. The shear force that caused failure of the concrete stiffness. surrounding the dowel was considered the ultimate shear The beam model consists of 8700 elements of type C3D8R strength of the dowel, which indicates the ability to sustain (8-node, reduced-integration 3-D linear brick element). A finer overloading and maintain stiffness under a large number of mesh was modeled for the dowels and concrete around the repeated loads. In addition, the slope of the curve character- dowel to allow for a more detailed analysis of the critical sections izes the stiffness of the tested dowel-concrete interaction. The surrounding the dowel. Although more computational time ultimate shear and stiffness associated with each dowel indicate is needed for the finer mesh, the higher mesh density allows for how the load transfer efficiency might be affected by dowel more accurate analysis of the strains, stresses, and deflections misalignment. at the most relevant points. A coarser mesh was assigned to the concrete not surrounding the dowel because less precision was needed in this area and to reduce the computational time 2.3.3 Analytical Modeling without significantly decreasing the accuracy of analysis. This section provides a brief overview of the finite element Two separate material models were employed to model modeling conducted in this study (a more detailed description the concrete. Following Prabhu et al. (2006), the concrete is provided in Appendix D). surrounding the dowel was modeled using the "concrete damaged plasticity" option available in ABAQUS. The inelastic behavior of concrete was modeled using the concept of isotropic 2.3.3.1 Finite Element Models damaged elasticity in combination with isotropic tensile and compressive plasticity (ABAQUS, 2007). This model accounts To model the effects of dowel misalignment on concrete for the loss of elastic stiffness due to plastic straining of the pavement behavior, the following 3-D ABAQUS models were concrete in tension and compression. The concrete away from developed using the approach developed by Khazanovich the dowel was modeled as a linear elastic material. et al. (2001): The dowel was modeled as an elastic isotropic material, with 20 elements along its length and 20 elements in the cross- Beam model replicating the laboratory test with individual section. A finer mesh in the dowel compared to the surround- dowels. ing concrete was necessary to improve the stability of the Slab model with four dowels for analysis of the effect of dowel-concrete interaction that was modeled as a surface-to- nonuniform dowel rotation on joint load transfer efficiency. surface contact defined between two deformable bodies. Initially for the pullout testing, the clamping mechanism The beam model for dowel-concrete interaction was cali- was set to be very stiff, and the shear-pull clamp was set at a brated using results of the laboratory tests. The calibrated very low stiffness. A stable friction contact between the dowel model then was used to investigate misalignment cases and and the surrounding concrete was ensured using the procedure magnitudes that were not tested. To analyze the effect of developed by Khazanovich et al. (2001). This was followed by multiple dowels, a slab model was built using this dowel- the application of the prescribed pullout displacement at the concrete interaction model. end of the dowel to simulate the displacement-controlled mode Based on the results of the finite element modeling, the of the laboratory testing. After the dowel reached the maximum concept of an equivalent dowel diameter was developed. The prescribed displacement, the displacement at the end of the effects of dowel misalignment on long-term pavement per- dowel was deactivated to simulate the removal of the test load. formance were then estimated using this concept and the After the pullout test simulation was completed, the prop- MEPDG performance prediction models. erties of both clamping mechanisms were changed to simulate stiff shear-pull clamping fixtures and negligible stiffness of Beam Model. A single finite element model was used to the pullout fixtures. This was followed by the application of the simulate both modified pullout and shear pull laboratory tests. prescribed shear-pull displacement at the end of the dowel. In the lab, shear testing always was conducted after the pullout testing to model the effect of joint opening prior to wheel Model Validation. To validate the finite element dowel- loading. In a similar manner, the finite element beam model concrete interaction model, the simulated deflections from was set up to apply the pullout test prior to applying the shear the beam model were analyzed in the same manner as the pull test, therefore accounting for damage in the concrete beam. deflections measured in the tests. The relative vertical dis- Thus, it was necessary to add or remove the clamping mech- placements of the dowel end (with respect to the surrounding anism when changing the simulation from pullout to shear concrete) were estimated. These laboratory-measured relative testing. This was accomplished by modeling the horizontal displacements and shear force data were used to validate the

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12 12,000 Table 2.3. ABAQUS-computed versus laboratory-measured shear capacities for various 8,000 dowel embedment lengths. Shear Force, lbs. Shear Capacity (lb) Embedment ABAQUS Laboratory Analytical Length (in.) Calculated Measured 4,000 Laboratory 2 4870 5360 3 6590 5930 4 7950 7050 0 5 9070 N/A 0 0.01 0.02 0.03 0.04 0.05 0.06 6 9890 9770 Relative Dowel Displacement, in. 9 10,370 9570 Figure 2.13. Laboratory and analytical shear versus displacement for an aligned dowel. analytical estimates. The figure indicates similar shear stiffness for the model and laboratory data with respect to the shear finite element model. The displacement measurement loca- capacity. The shear force at failure was used in the labora- tions used in the laboratory also were used in the finite element tory analysis while the shear force required to cause 0.05 in. model calculations so that the relative dowel displacement data [1.27 mm] of relative displacement was used in the finite obtained in the lab could be compared directly to the finite element analysis. element results. By comparing the results of the shear-pull tests Table 2.3 compares the shear capacities obtained from the to those of the ABAQUS model, rational parameters were lab testing to those estimated from the calibrated analytical established for the dowel-concrete interaction model. model for all of the embedment lengths. There is a consistent Figure 2.13 shows the shear force versus relative displace- agreement between the laboratory testing and analytical model ments for an aligned dowel tested in the laboratory and for results with the largest difference being less than 1 kip [4.45 kN]. a simulated dowel using ABAQUS. The figure shows some Thus, the analytical model can be applied to those cases for agreement between the model and laboratory results. Similar which lab testing was not feasible. observations were made for the other alignment conditions. Slab Model. Although the beam finite element model is The shear capacity was used to compare the performance of an effective tool for analyzing the effects of longitudinal and the dowels in the ABAQUS simulations to that obtained from vertical translations on the behavior of individual dowels, laboratory measurements. Figure 2.14 illustrates the shear previous laboratory and analytical studies indicated that the force versus relative displacement for a reduced embedment effects of dowel rotational misalignments (in the form of length of 6 in. [152 mm] and the most extreme case of reduced horizontal skew and vertical tilt) are affected by the mis- embedment length of 2 in. [51 mm] for both laboratory and alignments of other dowels in the joint (Tayabji, 1986; Khazanovich et al., 2001; Prabhu et al., 2006). To investigate this phenomenon, the beam model was expanded to simu- 12,000 late a slab with multiple dowels in the joint and to consider temperature expansion and contraction, as well as wheel Laboratory (6 in. embedment) loading at the joint. Analytical (6 in. embedment) 8,000 Laboratory (2 in. embedment) The slab model consists of two slabs connected by four Shear Force, lbs. Analytical (2 in. embedment) dowels at the joint and resting on an elastic Winkler foundation. Each slab is 60 in. [1524 mm] wide and 90 in. [2286 mm] long. 4,000 The symmetrical boundary conditions along one of the longi- tudinal slab edges make the effective slab width 120 in. [3 m]. These boundary conditions also reduce the model run time 0 by more than half (with respect to a full-scale model) without 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 affecting accuracy. To limit the effect of the reduced slab Relative Displacement, in. length in the longitudinal direction, the ends of the slab along Figure 2.14. Laboratory and analytical sheer versus the outside longitudinal edges were constrained by springs. A displacement for misaligned dowels. comparison of this model with a full-scale, four-slab ISLAB2000

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13 model (Khazanovich et al., 2000) found that the difference in In the absence of an input parameter for dowel misalign- LTE at the slab corner was within one percent. ment in the faulting model, the use of the equivalent dowel As in the beam model, a finer element mesh was used for diameter concept to account for the effects of dowel misalign- the dowels and the concrete surrounding the dowels; a total ment is proposed. The equivalent dowel diameter is the dowel of 30,464 type C3D8R elements (8-node, reduced-integration diameter that will yield the same dowel shear capacity of a mis- 3-D linear brick, continuum element) were used in this model. aligned dowel. This equivalent dowel diameter can then be used The model design was selected to optimize the computational to investigate the effect of dowel misalignment on the long- time without significantly influencing the accuracy. However, term pavement performance using the MEPDG procedures. each individual slab simulation required 4 hours or more of run The equivalent dowel diameter concept postulates that, time on a supercomputer. The concrete and dowel materials, with regard to joint faulting, a joint with misaligned dowels as well as the interface between the dowel and concrete, were behaves as a joint with aligned dowels with a diameter, deq, as assumed to have the same properties as those used in the beam defined by the following equation: model. Each dowel could be rotated about the vertical or horizontal axes to simulate uniform and different types of deq = remb rcc rvt rhs d0 (4) nonuniform misalignments. where To initiate the dowel-concrete contact, the same procedure remb = the adjustment factor for a reduction in embedment used in the beam model was used. After that, prescribed longi- length; tudinal displacements were applied at opposite transverse edges rcc = the adjustment factor for a reduction in concrete of the modeled slab to simulate temperature contraction of the cover; concrete slabs. The resulting joint opening induced damage in rvt = the adjustment factor for vertical tilt; the concrete surrounding the misaligned dowels. The analysis rhs = the adjustment factor for horizontal skew; and showed that misalignment of 2 in. per 18 in. [51 mm per d0 = the nominal dowel diameter. 457 mm] of vertical tilt causes higher stresses in the concrete surrounding the dowels than the aligned dowels. The adjustment factors can have values ranging from 0 to 1, After the joint opening was simulated, the prescribed dis- where the value is inversely related to the level of misalignment. placements were deactivated, and the simulated wheel load was For a perfectly aligned dowel, all adjustment factors are equal then applied at the corner of the slab causing displacements to 1 and the corresponding equivalent dowel diameter is the of the system. The ratio of displacements of the loaded and same as the design dowel diameter. Conversely, dowels that unloaded slabs provides a measure of the LTE for different are extremely misaligned in some way will have adjustment levels of dowel rotation. factors that approach zero. For example, if the dowel embed- ment length is equal to zero, then the adjustment factor remb 2.3.3.2 Performance Prediction Models is zero, making the equivalent dowel diameter zero, and the MEPDG faulting model would treat it as an undowelled pave- The MEPDG (AASHTO, 2008)does not include an input ment. Derivations of each individual dowel adjustment factor parameter for dowel misalignment. However, the laboratory are presented in Chapter 3. and field data and analysis conducted in this study provide a means for incorporating the effect of dowel misalignment in Transverse Cracking Model. The field, laboratory, and the MEPDG. The following section discusses approaches for finite element investigations conducted in this study could accounting for the effects of dowel misalignment in the models not link dowel misalignment with transverse cracking. used in the MEPDG for JPCP joint faulting, transverse crack- ing, joint spalling, and IRI models. Spalling Model. The MEPDG spalling model accounts only for the damage due to combinations of concrete degra- Faulting Model. Dowel diameter is one of the most impor- dation (controlled by the inputs of air content, water/cement tant parameters of the faulting model. Dowel design has a major ratio, and climate), and ability of incompressibles to penetrate effect on the LTE of JPCP joints. If all other parameters are the joint (controlled by the inputs of sealant type). The MEPDG equal, a joint with a greater dowel diameter will have a higher spalling model does not contain any parameters related to LTE, which according to the MEPDG faulting model should dowel diameter or misalignment in either of these factors. reduce the rate of faulting development. The laboratory and The model addresses only spalling due to concrete degradation analytical studies showed that dowel misalignment may affect and age. dowel shear capacity and cause accelerated development of Since dowel misalignment due to reduced concrete cover joint faulting. does not greatly influence the aging or wearing of joints,

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14 incorporating dowel misalignment into the original MEPDG where spalling model could not be rationally suggested. On the other C1 through C4 = weighting factors or coefficients and hand, dowel misalignment that reduces the concrete cover to IRI = predicted IRI, in./mi; the extent that the dowels are exposed at the surface is a road- IRII = initial IRI, in./mi; way safety concern and is therefore considered in this study CRK = % slabs with transverse cracks (all sever- (recommendations for concrete cover to minimizing the risk ities); of such critical spalling are presented in Chapter 3). SPALL = % joints with spalling (medium and high severities); IRI Model. The MEPDG IRI model considers changes in TFAULT = total joint faulting cumulated per mi, in.; ride quality over time as a degradation of the initial smoothness and due to transverse cracking, spalling, faulting, and pavement site SF = site factor. conditions. The general equation for the IRI model is presented below to illustrate the compound effect of predicted transverse If each of these components is affected by dowel misalign- cracking, spalling, and faulting on prediction of pavement ride ment in some fashion, then the IRI model will account for the quality (AASHTO, 2008): effects of dowel misalignment on IRI. Therefore, the MEPDG IRI model can be adopted in its current form to account for IRI = IRII + C1 CRK + C 2 SPALL + C3 TFAULT + C 4 SF (5) the effects of dowel misalignment.