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24 Table 3.5. Shear capacities for different levels of misalignment. Longitudinal Translation Vertical Translation Vertical Tilt Dowel Diameter Embedment, Shear Concrete Shear Rotation, Shear Diameter, Shear in. Capacity, lbs. Cover, in. Capacity, lbs. in./18 in. Capacity, lbs. in. Capacity, lbs. 2 4900 3.25 10400 0 10400 1.0 5600 3 6600 4.25 12000 0.5 10300 1.125 6800 4 8000 5.25 13400 1.0 10200 1.25 8000 5 9100 7.25 14600 1.5 10300 1.375 9200 6 9900 2.0 9700 1.5 10400 9 10400 causing failure in the laboratory (see Figure 2.13). Therefore, Case 1: All dowels rotated by the same amount, but adjacent the ultimate shear forces for dowel misalignments that could dowels are rotated in opposite directions. not be investigated in the laboratory can be estimated analyt- Case 2: Each dowel tilted with the same magnitude and in ically as the shear force corresponding to 0.05 in. [1.3 mm]. the same direction. Table 3.5 gives the ultimate shear capacities for different Case 3: The dowel in the wheel path aligned properly, and levels of longitudinal translation, concrete covers, vertical tilt, each other dowel rotated with the same magnitude and and dowel diameter. The table shows that the shear capacity of direction. a dowel is reduced by increasing levels of longitudinal transla- Case 4: The dowel at the wheel path rotated, and each other tion (reduced embedment length), increased by increasing dowel aligned properly. concrete cover, and not affected by the magnitude of vertical tilt. These results are similar to those observed from the laboratory For each case, joint LTE was calculated as the ratio of the tests except for the case of 4 per 18 in. [102 per 457 mm] tilt. corner deflection of the unloaded slab to the corner deflection It also should be noted that the beam test does not account for of the loaded slab. Table 3.6 shows LTE for these four cases with the effect of interaction with multiple dowels which could be different levels of dowel rotation. LTE is lower for the oppositely important for vertical tilt. The data also show that reductions in misaligned dowels especially as the dowel tilt exceeds 1 in. dowel diameter reduce the shear capacity and shear stiffness. per 18 in. [25 mm per 457 mm]. Thus, although the mean misalignment level of Case 2 was higher than Case 1 (the 3.3.2 Finite Element Slab Model mean misalignment is zero in Case 1), Case 1 results in a lower joint LTE. Therefore, the mean misalignment level is required The laboratory tests indicated that dowel rotations up to for characterizing the translational misalignments, but the 2 in. [51 mm] or less per 18 in. [457 mm] of dowel length did standard deviation of the dowels is required to describe the not result in significantly different dowel-concrete system rotational joint misalignment. Table 3.6 also shows that, responses under loading. A similar trend also was observed for the same magnitude of dowel tilt, the LTE is lower for from the analytical simulations. However, previous studies Case 4 than for Case 3, especially at the higher misalignment (Khazanovich et al., 2001) have shown that rotations of adja- levels. Thus, the alignment of the dowel in the wheel path cent dowels or multiple dowels in a single joint can influence (critical dowel) has a more significant effect on the LTE than the behavior of the joint. To investigate this effect, a slab model with multiple embedded dowels was considered. The the alignment of the other dowels in the joint. material parameters obtained from the beam model were used to simulate dowel performance using the slab model for the following four cases of rotational combinations: 3.4 Pavement Performance Modeling 3.4.1 Faulting Table 3.6. LTE predictions for various levels of dowel rotation. The equivalent dowel diameter concept requires the consid- eration of adjustment factors for each type of misalignment. LTE, percent Dowel Tilt, in./18 in. Case 1 Case 2 Case 3 Case 4 The development of such factors is presented in this section. 0.5 84.5 86.0 85.7 84.9 0.75 84.1 85.3 85.3 84.4 1 82.0 83.5 85.1 83.2 3.4.1.1 Embedment Length Adjustment Factor 1.25 81.0 82.9 85.1 - 1.5 79.5 82.1 85.2 82.3 The finite element model was used to obtain the embedment Average LTE 82.2 84.0 85.3 83.7 length adjustment factor. A series of finite element runs were

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25 12000 the nominal dowel diameter. Therefore, the adjustment factor for an embedment length of 5 in. [127 mm] is 1.4/1.5 = 0.933. 10000 Figure 3.13 presents the computed adjustment factor remb for a range of the embedment lengths Lemb. This relationship can Ultimate Shear Force, lbs. 8000 be presented by the following equation: 6000 remb = -0.010 Lemb 2 + 0.167 Lemb + 0.324 (6) 4000 where Lemb is the embedment length in inches. Equation 6 is applicable for embedment lengths between 2000 2 and 6.9 in. [51 and 175 mm]. An adjustment factor of 1 should be assumed for embedment lengths greater than 6.9 in. 0 [175 mm] and 0 for embedment lengths less than 2 in. [51 mm]. 0 2 4 6 8 10 In cases where the embedment length of the dowels varies Embedment Length, in. along the joint, this procedure will result in a different equiv- Figure 3.11. Dowel shear capacity versus embedment alent dowel diameter for each dowel in the joint. However, length for 1.5-in. [38 mm] diameter dowels. because the MEPDG faulting model assumes the same diam- eter for all dowels, a single equivalent dowel diameter that accounts for all dowels needs to be estimated. made. The first series was performed for a 1.5-in. [38-mm] Finite element modeling shows that the LTE of the joint diameter dowel with embedment lengths varying from 2 to is affected by misalignment of the dowel in the wheel path 9 in. [51 to 229 mm] and for dowel diameters ranging from approximately as much as the combined effect of the same 1.0 to 1.5 in. [25 to 38 mm] with a 9 in. [229 mm] embedment. level of misalignments for all of the other dowels in the joint Figures 3.11 and 3.12 present the relationships between embed- (see Table 3.6). Therefore, the following procedure should be ment length and shear capacity and between dowel diameter used for a joint with variable dowel embedment lengths: and shear capacity, respectively. By equating the shear capacity of a misaligned dowel with 1. Compute an adjustment factor for each dowel in the joint. the shear capacity of an aligned dowel of reduced diameter, an 2. Determine the mean adjustment factor for all of the dowels equivalent reduced dowel diameter could be determined. For in the joint. example, a 1.5-in. [38-mm] dowel with embedment of 5 in. 3. Determine the mean adjustment factor for the three dowels [127 mm] has a shear capacity of 9000 lb [40 kN] (Figure 3.14), in the critical wheel path (for example, the right wheel path which is equivalent to that of a 1.4-in. [36-mm] diameter dowel in the truck lane). with embedment of 9 in. [229 mm]. The adjustment factor then 4. Use the average of the two values obtained in Steps 2 and is calculated by dividing the corresponding dowel diameter by 3 as the adjustment factor for the joint. 12,000 1.2 10,000 Ultimate Shear Force, lbs. Correction Factor (remb) 8,000 0.8 6,000 4,000 0.4 2,000 0 0.0 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 0 1 2 3 4 5 6 7 8 9 Dowel Diameter, in. Embedment Length, in. Figure 3.12. Dowel shear capacity for various dowel Figure 3.13. Adjustment factor (remb) versus diameters (embedment length equal to 9 in. [229 mm]). embedment length.

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26 3.4.1.2 Vertical Translation (Low Concrete Cover) [25 mm] should be expected for concrete thicknesses above Adjustment Factor 12 in. [305 mm]. Therefore, reduction in shear capacity should be considered only if the reduction in concrete cover Laboratory beam testing was conducted only for nonverti- exceeds the normal variability level, as represented by the cally translated dowels and dowels with a vertical translation following equation: of 2 in. [51 mm] (representing concrete covers ranging from 1.25 in. to 3.375 in. [32 mm to 86 mm]). The finite element DSC = [ -153.3(CCref 2 - CC 2 ) + 2503(CCref - CC )] d0 (8 8) beam model was used to extend the results of the laboratory tests to concrete covers up to 7.25 in. [184 mm]. Dowels where 1.25 in. and 1.5 in. [32 mm and 38 mm] in diameter were used DSC = the change in dowel shear capacity in pounds due in the analysis for concrete covers of less than 5.25 in. [133 mm], to reduction in concrete cover beyond normal and only 1.5-in. [38-mm] diameter dowels were used for con- variability; crete covers of 5.25 in. [133 mm] and greater (because 1.5-in. CC = the concrete cover in inches; and [38-mm] diameter dowels are commonly used in thick pave- CCref = the reference level concrete cover in inches. ments that result in these large concrete covers). This analysis produced the following relationship between dowel shear CC and CCref can be computed as follows: capacity and concrete cover: CCref = HPCC 2 - d0 2 - 0.5, for H PCC 12 in . DSC = ( -153.3 CC 2 + 2503 CC ) d0 (7) CCref = HPCC 2 - d0 2 - 1.0, for H PCC > 12 in . (9) where CC = HPCC 2 - d0 2 - HPCC 2 - Ddepth DSC = the dowel shear capacity in lbs; d0 = the dowel diameter in inches; and where CC = the concrete cover in inches. HPCC = the designed PCC thickness in inches; d0 = the designed dowel diameter in inches; and Figure 3.14 presents the relationship between concrete Ddepth = the depth of the dowel in inches. cover and shear capacity for two dowel diameters obtained from model simulations and the laboratory test data. However, if the computed CCref > 3.5 d0, then 3.5 d0 should Figure 3.14 illustrates the reduction in shear capacity due be used as the CCref. This maximum value was selected based to a reduction in concrete cover. The field measurements on the results showing no increase of dowel shear capacity for conducted in this study showed that vertical translation of concrete cover exceeding 3.5 times the dowel diameter. up to 0.5 in. [13 mm] should be expected for concrete thick- If CC is equal to or greater than the reference concrete nesses of 12 in. [305 mm] or less, and a study conducted by cover (CCref), no reduction in effective dowel diameter should MTO (MTO, 2007) concluded that translation of up to 1 in. be considered (i.e., rcc = 1.0). If CC is less than 2 in. [51 mm], the adjustment factor should be considered to equal 0 (i.e., rcc = 0) because of high spalling potential. Effective dowel diameters 16000 1.5 in. Laboratory should be considered for intermediate values. 1.5 in. ABAQUS Figure 3.15 presents the relationship between dowel diam- 1.25 in. Laboratory 1.25 in. ABAQUS eter and dowel shear capacity obtained from finite element 12000 1.5 in. Equation 7 analysis for HPCC equal to 8 in. [203 mm]. The relationship Shear Capacity, lbs. 1.25 in. Equation 7 between the reduction in normalized shear capacity and the reduction in dowel diameter from d0 to d is presented as 8000 follows: 4000 DSC = 9628 ( d0 - d ) (10) Thus, the adjustment factor for concrete cover rcc can be pre- 0 sented as follows: 0 1 2 3 4 5 6 7 8 Concrete Cover, in. d 1 DSC rcc = = 1- (11) Figure 3.14. Shear capacity versus concrete cover. d0 9628 d0

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27 12000 diameter. The figure indicates that the adjustment factor decreases as the vertical translation increases; the decrease Change in Shear Capacity is less drastic for thicker concrete slabs because of the larger concrete cover. Ultimate Shear Force, lbs. 8000 Finite element analysis showed that the LTE near the slab corner is affected by the dowel in the wheel path as much as Change in all of the other dowels in the joint combined. Therefore, the Dowel Diameter 4000 following procedure should be used for a joint with variable concrete cover: 1. Compute an adjustment factor for each dowel in the joint. 0 2. Determine the mean adjustment factor for all of the dow- 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 els in the entire joint. Dowel Diameter, in. 3. Determine the mean adjustment factor for the three dow- Figure 3.15. Shear capacity versus dowel diameter. els in the critical wheel path (for example, the right wheel path in the truck lane). 4. Use the average of the two values obtained in Steps 2 and Substituting Equation 8 into equation 11 results in the 3 as the adjustment factor for the joint. following adjustment factor for each individual dowel: 3.4.1.3 Rotation (Horizontal or Vertical Tilt) rcc = 1 - -153.3 (CCref ) + 2503 (CCref ) + 153.3(CC ) 2 2 Adjustment Factor - 2503 (CC ) 9628 (12) Dowel rotation in the form of vertical tilt and horizontal skew can have adverse effects on the performance of concrete pavement joints. Increased restraint to joint opening and However, the adjustment factor should be assumed to closing due to dowel rotation may cause micro-damage and be zero for concrete covers less than 2 in. [51 mm] because minor spalling around dowels (as observed in the laboratory low concrete cover can cause spalling around the dowel. Even tests) that reduce joint LTE. Laboratory tests and analyses have if spalling is not visible, the ability of the dowel to transfer shown similar effects for vertical tilt and horizontal skew. the load will be diminished. Figure 3.16 presents the cal- culated dowel diameter adjustment factors versus vertical Therefore, the equivalent dowel diameter concept can be translation for combinations of PCC thickness and dowel applied in a similar manner to both types of misalignment. The equivalent dowel diameter concept used to account for the effects of translational misalignments also is used to account for the effects of rotational misalignments. As noted earlier, 1.1 relative rotations of dowels (e.g., opposite misalignment) have a greater effect on the joint performance than rotational mag- 1 nitude. The effect of rotational misalignments on joint LTE was determined by analyzing slabs with multiple dowels. In this 0.9 analysis, the corner deflections of the loaded and unloaded Correction Factor 13 in. thick - 1.5 in. dd slabs were computed for various combinations of dowel 0.8 10 in. thick - 1.5 in. dd misalignment. The joint LTE was calculated by dividing the 13 in. thick - 1.25 in. dd 10 in. thick - 1.25 in. dd unloaded slab corner deflection by the loaded slab corner 0.7 8 in. thick - 1.25 in. dd deflections, and the nondimensional joint stiffness, JStiff, was determined using the following equation (Khazanovich and 0.6 Gotlif, 2002): 0.5 -1.17786 -6 -4 -2 0 2 4 6 1 - 0.01 Vertical Translation, in. LTE JStiff = 0.012 (13) Figure 3.16. Concrete cover adjustment factors (rcc) versus vertical translation for combinations of dowel diameter and PCC thickness. in which LTE is expressed as a percentage.

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28 Finite element analysis was performed for each of the four 87 rotational misalignment cases described in Section 3.3.2, and 86 the joint stiffness was determined. Linear regression analysis y = 1.0001x R = 0.9376 was used to develop the following relationship: 85 Predicted LTE (%) 84 JStiff = JStiff 0 - 0.20623 MeanTilt - 0.61796 StDTilt 83 - 0.86862 WPTilt (14) 82 where 81 MeanTilt = the average tilt of the dowels in the joint in inches per 18 in.; 80 StDTilt = the standard deviation of the tilt of the dowels 79 in the joint in inches per 18 in.; and 79 80 81 82 83 84 85 86 87 WPTilt = the maximum dowel tilt in the critical wheel Finite Element Model Computed LTE (%) path in inches per 18 in. Figure 3.17. Computed versus predicted LTEs for various rotational misalignments. JStiff0 is the computed stiffness of the joint with aligned dowels; this value is presented in Table 3.7 for each dowel diameter. These joint stiffness values account for the contri- Based on these observations, joints with oppositely misaligned butions of the dowels to the stiffness of the joint, but not dowels with rotation of 0.5 in. per 18 in. [13 mm per 457 mm] those of aggregate interlock, foundation support, or other dowel length were used to represent the nominal condition. factors. Thus, any combination of dowel misalignment that results The joint LTE can be predicted using the following equation in a LTE equal to or greater than the nominal LTE will not (Crovetti, 1994): affect the pavement performance; rotations that result in less than the nominal LTE will have adverse effects on the 100% LTE = (15) joint performance. 1 + 1.2 ( JStiff ) -0.849 Table 3.8 gives the nominal load transfer efficiencies obtained from the finite element slab model for various dowel diameters; Figure 3.17 presents the load transfer efficiencies using lower LTE is obtained for smaller dowel diameters. The pre- Equations 14 and 15 versus the load transfer efficiencies dicted LTE can be expressed in terms of the diameter of a computed from the finite element analysis. These values properly aligned dowel, using the following relationship: correlate well. Figure 3.18 shows the sensitivity of predicted LTE to the d = 0.0103e 0.0582 LTE (16) level of tilt for uniformly and oppositely tilted 1.25-in. [32-mm] diameter dowels in a joint. The LTE decreases with increases in tilt level. The LTE values are lower for oppositely tilted 86 dowels than for uniformly tilted dowels. Similar observations Case 2: Uniformly Tilted were noted in earlier studies (Khazanovich et al., 2001). 84 The field study showed that construction practices should Case 1: Oppositely Tilted permit the installation of dowels with tilt no greater than 82 Predicted LTE (%) 0.5 in. per 18 in. [13 mm per 457 mm] of dowel length. Such a level of misalignment did not affect pavement performance. 80 78 Table 3.7. Computed stiffness for various 76 dowel diameters. Dowel Diameter (in.) JStiff0 74 1 6.537 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 1.125 7.447 Tilt, in./18 in. 1.25 8.461 1.375 9.601 Figure 3.18. Predicted LTEs for oppositely and 1.5 10.894 uniformly tilted dowels.

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29 Table 3.8. LTE versus dowel 40 diameter for slab model Aligned 35 simulations. Misaligned 30 Dowel Diameter, in. LTE 0.75 0.73 25 1 1.01 Stress, psi. 1.125 1.14 20 1.25 1.26 1.375 1.36 15 1.5 1.46 10 5 By substituting Equation 15 into Equation 16, the adjustment 0 factor for rotational misalignment (vertical tilt or horizontal 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 skew), rrot, is obtained as follows: Deflection, in. Figure 3.19. Longitudinal stresses for slabs d 0.0103 rrot = = exp ( 0.0582 LTE ) (17) between joints containing aligned and rotationally d0 d0 misaligned dowels. If the adjustment factor rrot is greater than 1, a value of 1 should be assumed. For small joint openings, the slab with misaligned dowels experienced slightly higher stresses than the slab with aligned 3.4.1.4 Faulting Prediction dowels at the joint. However, above a certain amount of joint After computing the adjustment factors for all misalignment opening, the slab with aligned dowels experiences consistently types, the equivalent diameter for the doweled joint should be higher stresses than the slab with misaligned dowels. This computed using Equation 4. The effect of dowel misalignment phenomenon is caused by damage in the concrete surrounding on the reduction of pavement life with respect to faulting the misaligned dowels, which reduces the ability of the joint and/or the reduction in predicted faulting reliability then can to resist opening. be determined using the MEPDG faulting model. Based on these observations, it can be concluded that dowel misalignment itself is not a sufficient cause for joint lockup and it does not cause significant additional stresses in the 3.4.2 JPCP Cracking longitudinal direction. Also, the MEPDG cracking model can be Joint lockup can cause transverse cracking. As discussed in used without modification to account for dowel misalignment. Section 2.3.3, if joint lockup causes significant longitudinal Several conditions were evaluated using the finite element stresses, then it can be accounted for by the MEPDG crack- slab model to investigate the effect of friction at the dowel- ing model. PCC interface. These conditions included a joint with aligned Earlier studies identified the possibility of high longitudinal dowels and a joint with two levels of misalignment (0.25 in. stresses as a result of rotationally misaligned dowels. One of [6 mm] over 18 in. [457 mm] and 2 in. [51 mm] over 18 in. these studies (Khazanovich et al., 2001) did not consider [457 mm]) for very high friction between the dowel and PCC. concrete damage in the immediate area of the dowel and over- Figure 3.22 shows the computed longitudinal stresses for estimated the joint capacity to resist opening. Another study these cases and the low friction cases for both an aligned and (Prabhu et al., 2006) indicated the possibility of large longi- a misaligned dowel. tudinal stresses for unrealistically large joint openings. Figure 3.20 indicates that aligned dowels with high friction To consider the effect of possible joint lockup on longitu- result in significantly higher longitudinal stresses and higher dinal stresses, the mid-slab stresses for aligned and misaligned resistance to joint opening than misaligned dowels with low dowels were considered. For the misaligned case, each dowel friction. Also notice that both the low and high friction cases was tilted by 2 in. [51 mm] over its 18 in. [457 mm] length, and for misaligned dowels did not converge for the entire range of the dowels were configured so that adjacent dowels were rotated joint openings (due to failure of concrete around the dowels). in opposite directions to provide the greatest potential for The analysis showed very high stress concentrations at the joint lockup. Figure 3.19 presents the computed longitudinal surface in the vicinity of the dowels, which may cause micro- stresses for various joint openings that represent different cracking or micro-spalling in the concrete around the dowels degrees of thermal contractions. and lead to joint lockup.

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30 250 The minimum recommended concrete cover should allow High Friction; 1 in./18 in. for adequate consolidation of concrete around dowels and Rotation 200 may be increased for aggregate with maximum size greater High Friction; than 1 in. [25 mm] based on local experience. Also, the min- 0.125 in./18 in. Rotation imum concrete cover may be increased if high possibility 150 for dowel corrosion exists. If the concrete cover is less than Stress, psi. High Friction; Aligned the minimum required concrete cover, the equivalent dowel 100 diameter should be set equal to zero (i.e., undowelled joint Low Friction; Aligned is assumed.) 50 Low Friction; 2 in./18 in. 3.4.4 Pavement Performance Prediction Rotation 0 The procedure for predicting pavement performance based 0 0.01 0.02 0.03 0.04 0.05 Deflection, in. on the measured dowel misalignment level requires that an equivalent dowel diameter be determined for each joint in a Figure 3.20. Effect of dowel-PCC friction on pavement using the MEPDG procedures. The following obser- longitudinal concrete stresses. vations were considered in formulating the performance pre- diction procedure: While misalignment can result in higher longitudinal stresses, The MEPDG prediction models were calibrated using the joint lockup is more greatly affected by friction between the data contained in the LTPP database for 500-ft [152-m] dowel and PCC. The laboratory tests identified the lack of long pavement sections. dowel grease as a cause for higher dowel-concrete interface Joints with severe dowel misalignment that are concentrated friction and significant increase of the maximum pullout force. in a certain portion of the pavement section will have a greater effect on performance than similar joints distributed randomly along the pavement project. 3.4.3 Joint Spalling Nondestructive dowel location devices could be used to In addition to joint performance considerations, the location investigate dowel misalignment in pavement projects. of dowels with respect to the top PCC surface may present The equivalent dowel diameter of each joint can be deter- constructability and safety concerns. In some cases, joints are mined using the equations provided in Chapter 3. not saw cut to the prescribed depth to avoid cutting through The mean value of a pavement design parameter (pavement the dowels located too close to the surface. In this case, joints thickness, subgrade resilient modulus, etc.) along the section will not be formed and random cracking occurs. Also, a com- is used. bination of vertical translation and tilt may result in low con- crete cover at the end of the dowel. This condition may cause The following procedure is suggested for analyzing the effects a high stress concentration in the concrete at the dowel end, of dowel misalignment on the performance of a uniform possibly leading to spalling and exposure of the dowel to the pavement project: pavement surface. To address safety concerns related to the low concrete cover, 1. Use dowel alignment measurements to calculate the equiv- it is recommended to saw cut through the dowels at the joint alent dowel diameter in each joint of the pavement project if any dowel end is located within 2 in. [51 mm] of the top using the procedure described in Section 3.4.1. pavement surface. This minimum concrete cover requirement 2. Establish "uniform sections" approximately 500 ft. [152 m] is supported by the findings of a full scale laboratory study in long for the purposes of analysis and evaluation such which a slab with 2 in. [51 mm] of concrete cover above the that all joints in the section have similar equivalent dowel dowel performed as well as a slab with 3 in. [76 mm] of cover diameters. A series of several joints in any section with for up to 10 million load cycles (Odden et al., 2003). Also, the relatively uniform equivalent dowel diameters that are laboratory testing conducted in this project showed that a substantially different from the others in uniform sections dowel with 1.25 in. [32 mm] of concrete cover sustained a may be evaluated as a separate uniform section. shear force of 4.5 kip [20 kN], which is greater than the force 3. Compute the mean equivalent dowel diameter for each required to be transferred by the critical dowel in a pavement section. Two or more adjacent sections with no significant joint loaded by a 60-kip [267 kN] tandem axle load (based on difference in equivalent dowel diameters can be combined ISLAB2000 analysis). into a single section.