Guidelines for Dowel Alignment in Concrete Pavements (2009) / Chapter Skim
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Attachment A - Recommended Guidelines for Dowel Alignment in Concrete Pavements
Attachment A - Recommended Guidelines for Dowel Alignment in Concrete Pavements
Pages 38-48
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From page 38... ...
Types and Definitions of Dowel Misalignment Dowel bars should be placed parallel to both the pavement surface and the longitudinal axis of the pavement in order to minimize longitudinal restraint of the transverse joints. Dowels are typically placed at mid-depth (to provide maximum shear load transfer capacity in the concrete slab)
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The following sections summarize the typical misalignment levels observed in the field in this study. Longitudinal Translation Field measurements indicated an average longitudinal dowel bar translation of 0.86 in.
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Dowel Rotation Dowel rotations about the horizontal and vertical axes (axial rotation is irrelevant for round dowels) are two forms of rotation that may significantly impact concrete pavement performance.
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of transverse joints. Misalignment Limitations While no clear relationship was found between moderate levels of dowel misalignment and pavement performance in terms of faulting, spalling or panel cracking, laboratory testing 41 Figure 5.
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4. Perform MEPDG computations for each uniform section using the calculated mean equivalent dowel diameter for the section, and compare the performance and distress predictions for each section with the prescribed performance thresholds or the as-designed pavement performance prediction.
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The reduced shear load capacity can be represented by a dowel diameter reduction factor for concrete cover, rcc, which is the ratio of the diameter of a dowel placed at mid-depth having the same shear capacity as the vertically translated dowel in question to that of the diameter of the misaligned dowel. The reduction in effective dowel diameter depends upon the amount of vertical translation, the typical amount of variation in vertical translation, and the assumed basic or reference amount of concrete cover.
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These data are used to compute the mean tilt or skew, standard deviation of the tilt or skew, and the maximum tilt or skew of the dowels in the critical wheel path. This information can then be used to estimate the stiffness of the joint and the joint load transfer efficiency (LTE)
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This value then can be used to determine the adjustment factor due to rotational misalignment, rrot, as follows (0.98 in this example) : Combined Effect The equivalent dowel diameter concept assumes that a joint with misaligned dowels behaves as a joint with perfectly aligned dowels of a smaller effective diameter, deq, as defined by the following equation: For the example illustrated above, the equivalent dowel diameter for the misaligned 1.5 in.
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Computation of Overall Effective Dowel Diameter The equivalent or effective dowel diameter is the original dowel diameter (d0) multiplied by the adjustment factors for concrete cover, embedment length, vertical tilt, and horizontal skew: rhs = ×( )
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. Assessment of a Pavement Section Problem Statement The following example illustrates the calculation of the effect of dowel misalignment on the performance of a 540-ft.
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showed that because of dowel misalignment, the reliability of faulting not exceeding the performance threshold was reduced from 96.7 to 91.9%, and the IRI reliability was reduced from 92.5 to 91.0%. Concluding Remarks The guidelines provide a simple methodology to account for the effects of dowel misalignment in estimating pavement performance.
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