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38 ATTACHMENT A Recommended Guidelines for Dowel Alignment in Concrete Pavements The proposed guidelines are the recommendations of Measuring dowel misalignment; NCHRP Project 10-69 staff at the University of Minnesota. Quantifying the effects of misaligned dowels on pavement These guidelines have not been approved by NCHRP or any performance; AASHTO committee or formally accepted for adoption by Determining critical levels of dowel misalignment that may AASHTO. result in lower levels of pavement performance; Preventing dowel misalignment; and Mitigating or remedying misaligned dowels in practice. Introduction and Background Transverse joints are designed to allow slab movements Types and Definitions of Dowel Misalignment due to shrinkage and thermal expansion/contraction while controlling the location and shape of slab cracks. Dowels are Dowel bars should be placed parallel to both the pavement installed in these joints to improve load transfer capacity across surface and the longitudinal axis of the pavement in order to the joints, thereby reducing slab deflections and stresses. minimize longitudinal restraint of the transverse joints. Dowels Dowels must be properly sized and placed to carry applied are typically placed at mid-depth (to provide maximum shear loads and minimize longitudinal restraint (i.e., to allow joints load transfer capacity in the concrete slab) and the dowel bar to open and close, as needed) and they must be fabricated should be centered longitudinally on the transverse joint. for durability (e.g., be resistant to corrosion or chemical Misalignment is deviation in dowel placement from the pre- attack). Dowels that are not located or oriented properly scribed position as a result of inaccurately placing the dowel, are called "misaligned" dowels. Misaligned dowels may not saw cutting in an incorrect position, dowel movement during provide adequate load transfer capacity and/or may pre- the paving operation, or a combination of these factors. vent the joint from opening and closing properly, resulting The five major categories of dowel misalignment, as illus- in premature pavement deterioration (e.g., joint faulting, trated in Figure 1, are horizontal translation, longitudinal trans- spalling, etc.). lation, vertical translation, horizontal skew, and vertical tilt Pavement dowels are generally installed using pre-fabricated (Tayabji, 1986). baskets or cages (which are placed on grade before concrete placement) or by using a mechanical dowel bar inserter Causes of Dowel Misalignment (mounted on the paving machine). Inspections of pavements in several states have shown that dowel misalignment generally Common causes of dowel misalignment when using basket occurs with both installation methods. These inspections have placement include: also shown that typical levels of misalignment do not always result in premature pavement distress. Use of basket assemblies that are bent or are otherwise faulty Requirements for dowel alignment were recently introduced due to inadequate rigidity (design), poor quality control based on limited in-service alignment and performance data during fabrication, or improper handling during transport (MTO, 2007; FHWA, 2007). The guidelines presented here and placement; are based on findings from field performance evaluation, Failure to anchor the basket assembly to the grade prior to laboratory testing, and analytical modeling and address the paving, thereby allowing the assembly to rotate, tip, or slide following topics: as the concrete is placed;

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39 Plan Plan Plan various degrees of accuracy. Because of the potential sensitivity of pavement performance to relatively small magnitudes of misalignment, measurement devices must be capable of pro- viding high precision. Horizontal Longitudinal Horizontal Among the devices used for measuring misalignment is the translation translation skew MIT Scan-2 (FHWA, 2007; FHWA, 2005; Yu and Khazanovich, 2005). Such measurement is performed by pulling the rail- Section Section mounted device along the joint while the device emits a weak, pulsating magnetic signal and detects the transient magnetic response signal. The included software which uses methods of tomography then determines the positions of the metal bars (ACPA, 2006). Available software can produce output in either Vertical Vertical translation tilt numerical or graphical forms. A recent evaluation concluded that such a device measures dowel placement with an accuracy Figure 1. Types of dowel misalignment (Tayabji, 1986). of 0.2 in. [5 mm] per 18 in. [457 mm] dowel length with 95 percent reliability on rotational alignment (FHWA, 2005). Use of improperly sized basket assemblies (i.e., too tall or too short); Typical Dowel Misalignments and Mishandling dowels or baskets during concrete placement Effects on Pavement Performance (e.g., workers stepping on dowel baskets); Inappropriate basket or cage width or placement that inter- Dowel misalignment is expected to occur on every project. feres with slipform paver operation, resulting in rotation For example, variations in constructed slab thickness will or sliding of the assembly; result in variability in concrete cover over the dowels. Also, Improper location of basket assembly; and the accuracy of basket placement or insertion points during Improper location of sawed or formed joint. construction or joint sawing or forming operations will influ- ence embedment lengths. The following sections summa- The most critical factor in using dowel basket assemblies is rize the typical misalignment levels observed in the field in probably the number and type of pins used to secure the this study. basket. When an insufficient number of pins (or inadequate pins) are used, the baskets may shift, rotate, or burst resulting Longitudinal Translation in misalignment problems (ACPA, 2006). Common causes of misalignment when using dowel bar Field measurements indicated an average longitudinal dowel inserters (DBI) include: bar translation of 0.86 in. [22 mm], with project standard deviations ranging from 0.4 to 1.9 in. [9 to 49 mm], and 1.2 in. Settlement of dowels in the concrete mass after insertion [30 mm] standard deviation for all individual dowels. (due to mix fluidity, excessive vibration, etc.); The overall distribution of longitudinal translation measure- Movement of inserted dowels due to mishandling after ments for individual dowels presented in Figure 2 shows that placement; more than 91 percent of all bars measured were within 2 in. Improper DBI operations; and [51 mm] of being centered on the transverse joint and about Improper location of sawed or formed joint. 98 percent were within 3 in. [76 mm]. The most critical factor in maintaining dowel alignment Vertical Translation when using DBI is probably the concrete mixture because it affects the ability of the DBI to accurately place dowels and Dowel bars are generally designed and assumed to be embed- control the dowel location and orientation in the plastic con- ded at the mid-depth of the slab. Dowels that are closer to the crete (ACPA, 2006). pavement top surface are considered to have a negative vertical translation and those that are closer to the bottom surface are considered to have a positive vertical translation. Detection/Measurement The average absolute value of vertical translation for the of Dowel Misalignment individual dowels measured for a large number of dowels was Many magnetometers, ground-penetrating radar units, and 0.46 in. [12 mm] with a standard deviation of 0.6 in. [15 mm]. other devices can provide indications of dowel alignment with The distribution of vertical translations of individual dowel

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40 25% 20% Percent of Bars 15% 10% 5% 0% 0.0 to 0.25 to 0.5 to 0.75 to 1.0 to 1.25 to 1.5 to 1.75 to 2.0 to 2.25 to 2.5 to 2.75 to 3.0 in to 0.25 in 0.5 in 0.75 in 1.0 in 1.25 in 1.5 in 1.75 in 2.0 in 2.25 in 2.5 in 2.75 in 3.0 in 6.5 in Longitudinal Translation, in. Figure 2. Distribution of longitudinal translation for field study measurements. bars shown in Figure 3 indicates that about 96 percent of all dowel with a standard deviation of 0.21 in. [5 mm]. Figure 4 bars were within 1.0 in. [25 mm] of the mid-depth location; presents the horizontal skew distribution for all dowels and the remaining dowels were more than 1 in. [25 mm] closer to shows that more than 60 percent of the bars were skewed by the top or bottom pavement surface. more than 1/4 in. [6 mm] per 18 in. [457 mm]. About 2 percent of the bars had horizontal skew values exceeding 0.75 in. [19 mm] and about 0.5 percent had horizontal skew values Dowel Rotation exceeding 1.0 in. [25 mm]. Dowel rotations about the horizontal and vertical axes (axial Vertical tilt averaged 0.23 in. [6 mm] per 18 in. [450 mm] rotation is irrelevant for round dowels) are two forms of dowel with a standard deviation of 0.21 in. [5.4 mm]. Figure 5 rotation that may significantly impact concrete pavement presents the vertical tilt distribution and shows a very similar performance. distribution to that of the horizontal skew. About 9, 2, and Measurements on a large number of dowels indicated an 1% of dowel bars had vertical tilt more than 0.50 in. [12 mm], average horizontal skew of 0.24 in. [6 mm] per 18 in. [457 mm] 0.75 in. [19 mm], and 1.0 in. [25 mm], respectively 35% 70% 30% 60% 25% Percent of Sections 50% 20% Percent of Bars 40% 15% 30% 10% 20% 5% 10% 0% 0% 1.0 in. < 0.25 in. 0.25 to 0.50 to 0.75 to 1.00 to 1.25 to 1.50 to Vertical Depth Deviation, in. 0.50 in. 0.75 in. 1.00 in. 1.25 in. 1.50 in. 3.50 in. Horizontal Skew, in. Figure 3. Distribution of vertical dowel bar translations. Figure 4. Distribution of the horizontal skew.

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41 70% inspected prior to and during the paving process. Damaged 60% baskets should be removed and replaced prior to placement of concrete. 50% The correct locations for dowels should be marked along both edges of the pavement for either basket or DBI place- Percent of Bars 40% ment methods. The marks must be placed accurately and 30% must be easy for the saw crew to locate after the paver has 20% passed (ACPA, 2005). Dowel baskets must be accurately placed in proper alignment 10% on the survey marks. A thorough inspection of basket and 0% dowel alignment prior to paving is extremely important. < 0.25 in. 0.25 to 0.50 to 0.75 to 1.00 to 1.25 to 1.50 to Dowel baskets must be firmly staked or anchored to ensure 0.50 in. 0.75 in. 1.00 in. 1.25 in. 1.50 in. 4.00 in. Vertical Tilt, in. that they do not move or tip during paving. Low anchor points help to prevent shoving and sliding of the basket while Figure 5. Distribution of vertical tilt. high anchor points help to prevent tipping of the basket (ACPA, 2005). The types of anchors used and the frequency of their use Summary of Misalignment Values should be selected based on the type and thickness of base An analysis of data from 60 project sites indicates that most used. For example, a 6-in. [152-mm] pin may be used to joints had dowel misalignments within the following ranges: firmly anchor the basket to an asphalt-treated base (ATB), but it may need to be installed on a skew if the layer thickness Longitudinal translation: 2 in. [51 mm] over 18-in. is 4 in. [102 mm]. [457-mm] dowels. There is no consensus with regard to the treatment of dowel Vertical translation: 0.5 in. [13 mm] for pavements 12 in. basket tie or spacer wires during construction. The FHWA [305 mm] or less in thickness. recommends that these wires should be removed, citing Rotational components (horizontal skew and vertical tilt): concerns that failing to cut the wires may contribute to joint each less than 0.5 in. [13 mm] over 18-in. [457-mm] dowels. lockup and subsequent slab cracking and notes that prop- erly anchored baskets do not need these wires for stability (FHWA, 1990). The American Concrete Pavement Asso- Measures for Reducing ciation (ACPA) recommends that dowel basket tie wires Dowel Misalignment should not be cut after basket placement and prior to paving Several measures can be taken to reduce the potential for because cutting the tie wires may destabilize the basket, dowel misalignment, as discussed in the following sections. allowing it to come apart during paving and result in mis- aligned dowels. ACPA also states that analyses show that concerns about the contribution of tie/spacer wires to Design Issues joint lock-up and subsequent slab cracking are unfounded Dowel baskets should be designed to withstand the rigors (ACPA, 2005). of transport, handling, and placement. Baskets that are Care must be taken during construction to avoid stepping not sufficiently rigid may bend or allow the dowels to be on the dowel baskets and dowels, especially during paving. moved during construction. When using a DBI, concrete mixtures should be selected to The use of narrower baskets, with the outside dowels located ensure stability of the dowel bars during placement and 9 to 12 in. [229 to 305 mm] from the pavement edge and subsequent paving operations (i.e., vibration, screeding, etc.) longitudinal joint (instead of 6 in. [152 mm]) reduces the To eliminate possible confusions between tie bars that are cost of the basket (one less dowel is used if spacing remains placed between adjacent lanes and/or shoulders and dowel constant) and reduces the probability of the paver catching bars that are placed at transverse joints, tie bars should not the dowel basket and shoving or twisting it during paving. be placed within 2 ft [0.6 m] of transverse joints. Construction Issues Misalignment Limitations Proper care must be taken in the storing and handling of While no clear relationship was found between moderate dowel baskets at the job site to prevent bending of the basket levels of dowel misalignment and pavement performance in or misalignment of the dowels. All dowel baskets should be terms of faulting, spalling or panel cracking, laboratory testing

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42 and analytical modeling determined that dowel misalignment 1. Use dowel alignment measurements to calculate the equiv- could reduce dowel shear capacity and its ability to transfer alent dowel diameter in each joint of the pavement project, a load. Therefore, limitations on dowel misalignment can be using the procedure described under "Joint Effectiveness based upon their effects on load transfer effectiveness, and Evaluation". by the minimum acceptable concrete cover (with respect to 2. Establish "uniform sections" approximately 500 ft [153 mm] either the top or bottom of the slab) or the depth of joint in length for the purpose of analysis and evaluation such saw cuts. that all joints in the section have similar equivalent dowel Dowel alignment guidelines and specifications should stip- diameters. A series of several joints in any 500-ft [153-mm] ulate requirements that are achievable with good construction section with equivalent dowel diameters that are rela- practices and have no significant adverse impact on pavement tively uniform but substantially different from the rest performance. However, specifications and guidelines should of the section may be evaluated as a separate uniform encourage placement that is as accurate as is reasonably pos- section. sible, and also recognize that certain levels of misalignment 3. Compute the mean equivalent dowel diameter for each may not significantly affect pavement performance. section. Two or more adjacent sections with no significant The following approach will help establish dowel placement difference in equivalent dowel diameters can be combined specifications: into a single section for analysis purposes. 4. Perform MEPDG computations for each uniform section 1. Establish constructible acceptance criteria. Establishing using the calculated mean equivalent dowel diameter for a relatively tight (but constructible) placement tolerance will the section, and compare the performance and distress promote the placement of properly aligned dowel bars and predictions for each section with the prescribed perfor- eliminate the need for further evaluation or remedial actions. mance thresholds or the as-designed pavement performance Examples of such tolerances may include the following: prediction. Horizontal or vertical rotational alignment: 0.5 in. [13 mm] over 18.0 in. [457 mm]. A decision about the acceptance, rejection, correction Vertical translation: + 0.5 in. [13 mm] for pavements factors, etc. can be made for each pavement section based 12 in. [305 mm] or less in thickness; + 1.0 in. [25 mm] on the results of the computations and stipulated threshold for pavements greater than 12 in. [305 mm] in thickness. values. If correction measures (such as dowel retrofitting) are Longitudinal translation: 2.1 in. [55 mm] over 18-in. performed, the effective dowel diameters of the affected joints [457 mm] dowels. should be recalculated and the pavement performance pre- Horizontal translation: 1 in. [25 mm]. dictions for those joints reassessed. 2. Establish rejection criteria. Rejection criteria should be established on the basis of measured, predicted, or expected pavement performance or behavior. For example, remedial Corrective Measures action may be required due to inadequate depth of place- ment (considering concrete cover requirements and saw cut The following corrective measures may be considered depth), inability to achieve specified performance thresholds appropriate for dowels or doweled joints that fail to meet the (e.g., predicted faulting or IRI), or obvious placement flaws acceptance criteria: (e.g., interference from misplaced tie bars). For example, a dowel, joint, or section may be rejected if any of the Dowel bar(s) with inadequate concrete cover or excessive following conditions occur: rotational misalignment can be corrected by removing and Concrete cover at any end of the dowel is 2 in. [51 mm] replacing the misaligned bars (retrofitting). or less from the top surface. Bar(s) in the wheel path that cannot be removed can be Concrete cover from the dowel to the top surface is less corrected by removing and replacing the entire joint than the sawcut depth. using a doweled full-depth repair. Rotational misalignment is 3 in. [75 mm] or more per Bar(s) not in the wheel paths that cannot be removed 18 in. [457 mm] dowel length. can be corrected by cutting completely through. Agency-specified performance prediction measures are Individual dowel bars with inadequate embedment or not met. that are missing can be corrected by retrofitting additional dowels. The following procedure may be used for analyzing the Average initial joint load transfer efficiency should not be effects of dowel misalignment on the performance of a uniform less than 70 percent after corrective measures have been pavement project: performed.

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43 Joint Effectiveness Evaluation Joint load transfer efficiency (LTE) is generally most affected by the dowel(s) closest to the applied load (generally in the The equivalent dowel diameter concept assumes that a wheel path), and the dowels in the wheel path affect LTE as joint with misaligned dowels behaves as a joint with perfectly much as the combined effects of all other dowels in the joint. aligned dowels of a smaller effective diameter. The equivalent The following procedure should be used if dowel embedment dowel diameter, deq, is defined by the following equation: varies along the joint: deq = remb rcc rvt rhs d0 1. Compute the adjustment factor for each dowel in the joint. where 2. Determine the mean adjustment factor for all of the dowels remb = adjustment factor for a reduction in embedment in the joint. length; 3. Determine the mean adjustment factor for the three dowels rcc = adjustment factor for a reduction in concrete cover; in the critical wheel path (for example, the right wheel path rvt = adjustment factor for vertical tilt (dowel rotation); in the truck lane). rhs = adjustment factor for horizontal skew (dowel rota- 4. Use the average of the two values obtained in Steps 2 and 3 tion); and as the adjustment factor for the joint. d0 = nominal dowel diameter. Concrete Cover Effect (Vertical Translation) The procedure for selecting appropriate adjustment factors for the different misalignment forms is described below. When the dowel is translated vertically, the amount of concrete cover is reduced either above or below the dowel, which reduces the shear load capacity of the concrete and of Embedment Effect (Longitudinal Translation) the dowel-concrete system. The reduced shear load capacity Figure 6 can be used to estimate the adjustment factor remb can be represented by a dowel diameter reduction factor (or dowel diameter ratio), for dowel embedment length, Lemb. for concrete cover, rcc, which is the ratio of the diameter of No reduction or adjustment is assumed for embedment of a dowel placed at mid-depth having the same shear capac- 6.9 in. [175 mm] or more, and embedment of 2 in. [51 mm] or ity as the vertically translated dowel in question to that of less should be treated as undoweled (i.e., remb = 0). The relation- the diameter of the misaligned dowel. The reduction in ship shown in Figure 6 is given by the following equation for effective dowel diameter depends upon the amount of ver- embedment lengths between 2 and 6.9 in.: tical translation, the typical amount of variation in vertical translation, and the assumed basic or reference amount of remb = -0.010 Lemb 2 0.167 Lemb 0.324 concrete cover. A reduction should be applied only when vertical translation exceeds normal variability and the result- For example, the adjustment factor, remb, for an 18-in. ing concrete cover is lower than a specified reference level [457-mm] dowel that is longitudinally translated by 3.9 in. of concrete cover. [99 mm] (i.e., 5.1 in. [130 mm] of embedment), is 0.916. The actual concrete cover (CC) for a given dowel can be calculated as follows: 1.2 CC = y d0/2, where y is the measured depth of the center of the dowel and d0 is the nominal dowel diameter if the longitudinal axis of the dowel is above mid-depth of the Correction Factor (remb) 0.8 pavement CC = HPCC y d0/2, where HPCC is the slab thickness if the longitudinal axis of the dowel is below mid-depth of the pavement (i.e., the dowel is closer to the bottom of the slab). 0.4 Alternatively, CC can be computed equivalently using the following single equation: 0.0 CC = HPCC 2 - d 0 2 - HPCC 2 - y 0 1 2 3 4 5 6 7 8 9 Embedment Length, in. The reference level of concrete cover, CCref, can be con- Figure 6. Adjustment factor for embedment length. sidered as the amount of cover above which there is no

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44 appreciable increase in dowel-concrete shear capacity (or below For example, the adjustment factor due to vertical translation which there is a decrease in dowel-concrete shear capacity). of a 1.5-in. [38-mm] dowel in a 11 in. [279-mm] thick concrete For any pavement thickness, the maximum possible concrete slab by 1.75 in. [44 mm] (i.e., concrete cover is decreased from cover, CCmax, is developed when the dowel is located at the a reference or "nominal" level of 4.25 in. [108 mm] to 3.0 in. exact mid-depth of the slab: [76 mm]) would be: CC max = HPCC 2 - d 0 2 = ( HPCC - d 0 ) 2 -153.3 4.252 + 2503 4.25 + 153.3 3.02 - 2503 3.0 rcc = 1 - 9628 Because there is some expected variability in concrete cover = 0.82 due to variances in constructed slab thickness, finished base profile, etc., the maximum possible value of concrete cover The following procedure is recommended for determining should be reduced by this amount of variability to serve as a the "average" effective diameter for dowels with variable basic reference level of concrete cover for evaluating the effects concrete cover at a particular transverse joint: of vertical dowel misalignment. Thus, one possible value of CCref is given as: 1. Compute an adjustment factor for each dowel in the joint. 2. Determine the mean adjustment factor for all of the dowels CC ref = HPCC 2 - d 0 2 - typ = ( HPCC - d 0 ) 2 - typ in the joint. 3. Determine the mean adjustment factor for the three dowels where typ = the typical variance in vertical dowel translation, in the critical wheel path (for example, the right wheel which is estimated to be 0.5 in. (13 mm) for slab thickness path in the truck lane). of < 12 in. (305 mm) and 1.0 in. (25 mm) for slab thickness 4. Use the average of the two values obtained in Steps 2 and 3 greater than 12 in (305 mm). as the adjustment factor for the examined joint. Finite element analysis indicates that increasing concrete cover beyond approximately 3.5 times the diameter of the dowel Rotational Effects (Vertical Tilt and Horizontal Skew) bar does not improve the shear capacity of the dowel-concrete system. Therefore, the reference level of concrete cover can be The effects of vertical tilt and horizontal skew have been defined as the lesser of the theoretical amount of concrete cover observed to be similar in both laboratory tests and analytical for a dowel at mid-depth of the slab less the typical vertical modeling. Therefore, the two adjustment factors, rvt and rhs, translation, or 3.5 d0. This is expressed as follows: are computed in the same manner but separately. Determining adjustment factors for vertical tilt and hori- CC ref = Min ( HPCC 2 - d 0 2 - 0.5, 3.5 d 0 ) zontal skew requires the measurement of vertical tilt and hori- zontal skew for each dowel in the joint. These data are used for slab thickness 12 in. [ 305 mm ] . to compute the mean tilt or skew, standard deviation of the tilt .0, 3.5 d 0 ) CC ref = Min ( HPCC 2 - d 0 2 - 1. or skew, and the maximum tilt or skew of the dowels in the crit- ical wheel path. This information can then be used to estimate for slab thickness > 12 in. [ 305 mm ] . the stiffness of the joint and the joint load transfer efficiency (LTE). LTE can be related to the average diameter of properly If the actual CC is greater than or equal to the reference aligned dowels to compute rvt and rhs, as illustrated below. level of concrete cover (CCref), no reduction in dowel diameter The following relationship between dowel tilt and non- should be considered (i.e., rcc = 1.0). If the actual CC is less than dimesional joint stiffness was developed: 2 in. [51 mm], then the adjustment factor should be assumed to be equal to 0 (i.e., rcc = 0). If the actual concrete cover is less JStiff = JStiff 0 - 0.20623 MeanTilt - 0.61796 StDTilt than the reference value (but greater than 2 in. [51 mm]), a - 0.86862 WPTilt reduction in effective dowel diameter should be considered. Laboratory testing and finite element analyses of dowels where embedded in 8-in. [203-mm] concrete slabs have provided JStiff = nondimensional stiffness of a joint with rota- the following relationship: tionally misaligned dowels; JStiff0 = the predicted nondimensional stiffness of a rcc = 1 - -153.3 ( CC ref ) + 2503 ( CC ref ) + 153.3 ( CC ) 2 2 joint with aligned dowels (see Table 1); MeanTilt = absolute value of the average tilt (or skew) of - 2503 ( CC ) 9628 the dowels in the joint, in. per 18-in. dowel;

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45 Table 1. Nondimensional joint stiffness values Example for Calculating the (JStiff0) for aligned dowels of various Equivalent Dowel Diameter dowel diameters. This example assumes an 11-in. [279-mm] thick pavement Dowel Diameter (in.) JStiff0 with joints containing 12 dowels with 18 in. [457 mm] length 1 6.537 1.125 7.447 and 1.5 in. [38 mm] diameter, with the following conditions: 1.25 8.461 1.375 9.601 1. The saw cut was incorrectly made 4 in. [102 mm] away from 1.5 10.894 the designed location, resulting in 4 in. [102 mm] of lon- gitudinal translation and 5 in. [137 mm] of embedment length for all 12 dowels. StDTilt = standard deviation of the tilt (or skew) of the 2. The dowel basket was 0.75 in. [19 mm] taller than was dowels in the joint; and required for the mid-depth dowel placement, resulting in WPTilt = maximum absolute value of the tilt (or skew) 0.75 in. [19 mm] vertical translational displacement towards of the dowels in the wheel path, in. per 18-in. the pavement surface and reduced concrete cover for all dowel. 12 dowels in the joint from 4.75 to 4 in. [121 to 102 mm]. 3. The rotational misalignments (vertical tilt and horizontal Example: Assume that the average measured horizontal skew skew) for all 12 dowels in the joint are given by Table 2. The of 1.5-in. [38-mm] diameter dowels in a joint is 0.2 in. [5 mm], dowels are numbered according to their distance from the with a standard deviation of 0.633 in. [16.1 mm] and that the truck lane shoulder (i.e., dowel Number 1 is the closest to maximum horizontal skew of the wheel path dowel is 0.8 in. the shoulder). The first three dowels are considered to be [20 mm]. The resulting nondimensional stiffness value would wheel path dowels. be 9.767. The nondimensional stiffness can be used to calculate LTE Calculation of Equivalent Dowel Diameter using the following relationship (Crovetti, 1994): Embedment Length Adjustment Factor 100% LTE = Because the embedment length is greater than 2 in. [51 mm] 1 + 1.2 ( JStiff ) -0.849 and less than 6.9 in. [175 mm], the adjustment factor due to the longitudinal translation and reduced embedment length, Thus for a nondimensional stiffness value of 9.767, the LTE remb, is computed as: would be 85.2 percent. This value then can be used to deter- mine the adjustment factor due to rotational misalignment, remb = -0.01 Lemb 2 + 0.167 Lemb + 0.324 rrot, as follows (0.98 in this example): remb = -0.010 (5 ) + 0.167 (5 ) + 0.324 = 0.909 2 0.0103 rrot = exp ( 0.0582 LTE ) d0 Table 2. Assumed dwell Combined Effect misalignments in the joint. The equivalent dowel diameter concept assumes that a Dowel Bar Vertical tilt, Horiz. Skew, Number in./18 in. in./18 in. joint with misaligned dowels behaves as a joint with perfectly 1 -0.44 -0.26 aligned dowels of a smaller effective diameter, deq, as defined 2 -0.50 -0.32 by the following equation: 3 -0.34 -0.32 4 -0.80 -0.38 deq = remb rcc rvt rhs d0 5 -0.54 -0.48 6 1.46 -0.27 For the example illustrated above, the equivalent dowel 7 -0.54 -0.39 diameter for the misaligned 1.5 in. dowels (assuming all of the 8 0.46 -0.33 misalignments occur concurrently and that there is no vertical 9 -0.54 -0.47 tilt) would be: 10 -0.54 -0.43 11 -0.54 -0.44 deq = 0.916 0.82 1.0 0.98 1.5 = 1.10 in. 12 -0.54 -0.42

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46 Vertical Translation (Reduced Concrete Cover) 0.0103 rvt = exp ( 0.0582 LTE ) Adjustment Factor d0 The reference and actual concrete cover values (CCref and 0.0103 CC, respectively) are computed as: rvt = exp ( 0.0582 85.51) = 0.995 1.5 CCref = the smaller of ( HPCC 2 - d 0 2 - 0.5 ) and 3.5d 0 Horizontal Skew Adjustment Factor = (11 2 - 1.5 2 - 0.5 ) or 3.5 1.5 For the horizontal skew measurements provided in Table 2 = 4.25 in. or 5.25 in. = 4.25 in. the following misalignment parameters are calculated: CC = HPCC - d 0 2 - HPCC 2 - y Mean horizontal skew = 0.38 in. [10 mm]. = 11 2 - 1.5 2 - 11 2 - 4.75 in. Standard deviation of horizontal skew = 0.073 in. [2 mm]. Maximum absolute value of wheel path dowel horizontal = 4.00 in. skew = 0.32 in. [8 mm]. Using these values of and CC, the adjustment factor due to The nondimensional joint stiffness can be calculated as: the loss in concrete cover, rcc, can be calculated as follows: JStiff = JStiff 0 - 0.20623 MeanTilt - 0.61796 StDTilt rcc = 1 - -153.3 ( 4.25 ) + 2503 ( 4.25 ) + 153.3 ( 4 ) 2 2 - 0.86862 WPTilt - 2503 ( 4 ) 9628 = 0.968 JStiff = 10.8942 - 0.20623 ( 0.38 ) - 0.61796 ( 0.073) Vertical Tilt Adjustment Factor - 0.86862 0.32 = 10.49 For the vertical tilt measurements provided in Table 2, the The LTE of the joint can be estimated as: following misalignment parameters are calculated: 100 Mean vertical tilt = 0.2 in. [5 mm]. LTE ( % ) = 1 + 1.2 ( JStiff ) -0.849 Standard deviation of vertical tilt = 0.633 in.[16 mm]. Maximum absolute value of wheel path dowel vertical tilt = 0.5 in. [13 mm]. 100 LTE = = 85.98% 1 + 1.2 (10.49 ) -0.849 The nondimensional joint stiffness is calculated as follows: The horizontal skew adjustment factor associated with this JStiff = JStiff 0 - 0.20623 MeanTilt - 0.61796 StDTilt load transfer efficiency can then be estimated as: - 0.86862 WPTilt 0.0103 rhs = exp ( 0.0582 LTE ) JStiff = 10.8942 - 0.20623 ( 0.2 ) - 0.61796 ( 0.633) d0 - 0.86862 0.5 = 10.03 0.0103 rhs = exp ( 0.0582 85.98 ) = 1.02 1.5 The LTE of the joint can be estimated as: Because the maximum allowable adjustment factor cannot 100 LTE ( % ) = exceed 1.0, an adjustment factor of 1.0 will be assumed. 1 + 1.2 ( JStiff ) -0.849 100 Computation of Overall Effective Dowel Diameter LTE = = 85.51% 1 + 1.2 (10.03) -0.849 The equivalent or effective dowel diameter is the original dowel diameter (d0) multiplied by the adjustment factors for The vertical tilt adjustment factor associated with this load concrete cover, embedment length, vertical tilt, and hori- transfer efficiency can then be estimated as: zontal skew:

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47 Table 3. Equivalent dowel diameter for each joint in the pavement section. Equivalent Equivalent Equivalent Dowel Dowel Dowel Joint # Joint # Joint # Diameter Diameter Diameter (in.) (in.) (in.) 1 1.31 11 1.5 21 1.21 2 1.5 12 1.22 22 1.5 3 1.41 13 1.5 23 1.5 4 1.14 14 1.5 24 1.27 5 1.5 15 1.49 25 1.5 6 1.1 16 1.5 26 1.5 7 1.5 17 1.5 27 1.5 8 1.5 18 1.23 28 1.5 9 1.5 19 1.05 29 1.37 10 1.5 20 1.5 30 1.5 deq = remb rcc rvt rhs d0 = 0.909 0.968 0.996 1 1.5 12 dowels with 18 in. [457 mm] length and 1.5 in. [38 mm] diameter. The pavement was designed with the following per- = 1.31 in. formance criteria after 20 years at 90 percent reliability: Therefore, to account for the effects of the misalignment in Transverse cracking not to exceed 12% of cracked slabs. this example, the pavement should be treated as if it had a Mean joint faulting not to exceed 0.12 in. [3 mm]. dowel diameter of 1.31 in. [33 mm] (and not 1.5 in. [38 mm] IRI not to exceed 160 in./mile [2.5 m/km]. diameter). The equivalent dowel diameters were calculated for the Assessment of a Pavement Section dowel alignments of each joint; results are shown in Table 3. Because the pavement section is less than 1000 ft [305 m], the Problem Statement mean equivalent dowel diameter is computed for the entire The following example illustrates the calculation of the pavement section resulting in 1.41 in. [36 mm]. This equivalent effect of dowel misalignment on the performance of a 540-ft. dowel diameter was then used in an MEPDG simulation to [165-m] pavement section with an 11 in. [279 mm] thickness. predict faulting and IRI for the project. Figures 7 and 8 present The pavement section has 30 joints, each of which contains the predicted faulting and IRI, respectively, for the as-designed 0.14 0.12 Performance Threshold 1.41 in. 0.10 1.5 in. 0.08 Faulting, in. 0.06 0.04 0.02 0.00 0 2 4 6 8 10 12 14 16 18 20 22 Pavement age, years Figure 7. Predicted faulting for the as-designed pavement project.

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48 240 200 Performance Threshold 1.41 in. 1.5 in. 160 IRI, in. / mile 120 80 0 2 4 6 8 10 12 14 16 18 20 22 Pavement age, years Figure 8. Predicted IRI for the as-designed pavement project. pavement (dowel diameter of 1.50 in. [38 mm]) and for a ARA (2005). Dowel Bar Alignments of Typical In-Service Pavements. similar pavement with 1.41 in. [36 mm] dowels. Publication SN2894. Portland Cement Association, Skokie, IL AASHTO (2008). Mechanistic-Empirical Pavement Design Guide: A The predicted faulting and IRI of the project after consid- Manual of Practice. Interim Edition. American Association of State ering the dowel misalignment effects are within the specified Highway and Transportation Officials, Washington, DC. acceptance thresholds. However, analysis of the MEPDG run Burnham, T. (1999) A Field Study of PCC Joint Misalignment near output files (not presented here) showed that because of dowel Fergus Falls, Minnesota, Report No. MN/RC-1999-29, Final Report. misalignment, the reliability of faulting not exceeding the Maplewood, MN: Minnesota DOT. Crovetti, J.A. (1994). Evaluation of Jointed Concrete Pavement Systems performance threshold was reduced from 96.7 to 91.9%, and Incorporating Open-Graded Permeable Bases. Ph.D. dissertation, the IRI reliability was reduced from 92.5 to 91.0%. University of Illinois at Urbana-Champaign, Urbana, IL. FHWA (1990). Concrete Pavement Joints. Technical Advisory T 5040.30. Federal Highway Administration, Washington, DC. November 30, Concluding Remarks 1990. FHWA (2005). Use of Magnetic Tomography to Evaluate Dowel Bar The guidelines provide a simple methodology to account Placement. TechBrief. Federal Highway Administration, Washing- for the effects of dowel misalignment in estimating pavement ton, DC. performance. The methodology uses an equivalent diameter FHWA (2007). Best Practices for Dowel Placement Tolerances. Tech- Brief. Federal Highway Administration, Washington, DC. concept in which dowel diameter is reduced to account for Fowler, G., and W. Gulden (1983). Investigation of Location of Dowel the effects of misalignment. The dowel diameter reduction Bars Placed by Mechanical Implantation, Georgia Department of factor depends on the type and level of misalignment. Equa- Transportation. Report No. FHWA/RD-82/153. Federal Highway tions for determining the reduction factor for different types Administration, Washington, DC. of misalignments were developed based on the results of field, Khazanovich, L., and A. Gotlif (2002). Evaluation of Joint and Crack Load Transfer. Final Report, FHWA-RD-02-088, Federal Highway laboratory, and finite element analysis. Pavement performance Administration, Washington, DC. can then be estimated using pavement analysis predictions MTO (2007). Ontario Provincial Standards for Roads and Public Works. (e.g., the MEPDG) for the reduced dowel diameter. Sections 350.04 through 350.08. Ontario Ministry of Transportation, Toronto, ONT, Canada. Tayabji, S.D. (1986). Dowel Placement Tolerances for Concrete Pave- Attachment A References ments. In Transportation Research Record 1062, National Research Council, Washington, DC, pp. 4754. ACPA (2005). The Relationship Between Sawed Joints and Dowel Bars. Yu, H.T. (2005). Dowel Bar Alignments of Typical In-Service Pavements. Concrete Pavement Progress, Vol. 41, No. 3. American Concrete R&D Serial No. 2894. Portland Cement Association, Skokie, IL. Pavement Association. Skokie, IL. March 30, 2005. Yu, H. T., and L. Khazanovich (2005). Use of Magnetic Tomography Tech- ACPA (2006). Evaluating and Optimizing Dowel Bar Alignment. SR999P. nology to Evaluate Dowel Placement. Report No. FHWA-IF-06-006. American Concrete Pavement Association, Skokie, IL. Final Report. Federal Highway Administration, Washington, DC.