 Original article
 Open Access
Effect of Dowel Bar Arrangements on Performance of Jointed Plain Concrete Pavement (JPCP)
 Kukjoo Kim^{1},
 Sanghyun Chun^{2}Email author,
 Sangyoung Han^{2} and
 Mang Tia^{2}
https://doi.org/10.1186/s4006901802761
© The Author(s) 2018
 Received: 13 July 2017
 Accepted: 18 April 2018
 Published: 29 May 2018
Abstract
A fullscale jointed plain concrete pavement (JPCP) with two different dowel bar arrangements, namely, standard and special method, was constructed and evaluated under actual trafficenvironmental condition in Florida. For standard dowel bar arrangement, dowel bars spaced at 304.8 mm (12 in), while three dowel bars spaced at 304.8 mm (12 in) only within the wheel paths were installed for special dowel bar arrangement. Field performance evaluation was conducted in terms of longitudinal crack, transverse crack, corner crack, spalling, and load transfer efficiency (LTE). Also, a threedimensional (3D) finite element (FE) model was developed to evaluate change in structural response characteristics due to different dowel bar arrangements under the critical loading condition. The developed FE model was used to perform a parametric analysis to determine the effects of different dowel bar arrangements. Results indicated that no significant changes in pavement structural responses, including the slab stresses and deflections, were predicted between two dowel bar arrangements that may result in no significant difference in expected performance for the test slabs evaluated, and this matched well with results of field performance evaluation. Also, it was indicated that the base modulus plays an important role on the doweljoint behavior and stiffer base condition could significantly improve the doweljoint performance. Therefore, when the base layer is stiff enough to support the slab deflection and resist erosion (e.g., AC layer), special dowel bar arrangement could provide similar performance as compared to standard dowel bar arrangement that result in significant cost savings without any negative effects on expected pavement performance.
Keywords
 dowel bar arrangement
 concrete pavements
 finite element analysis and longterm performance
1 Introduction
1.1 Background
Dowel bars are commonly used in jointed plain concrete pavements (JPCP) as a load transfer device across joints, especially for pavements with heavy traffic. The primary advantage of dowel bars is to transfer load without restricting horizontal joint movements due to temperature and moisture expansion and contraction in the concrete slabs. Also, dowel bars play a role to maintain the vertical and horizontal alignment of slabs. The load transfer efficiency depends on a number of doweljoint parameters, including modulus of dowel support, dowel bar diameter, dowel length, dowel bar spacing, dowel looseness, joint opening width, and subgrade strength (Channakeshava et al. 1993; Guo et al. 1993; Brill and Guo 2000; Kim and Hjelmstad 2003; Maitra et al. 2009).
Since the placement of dowel bars requires correct positioning, it tends to have correspondingly higher cost, including the increased construction time and construction material (i.e., dowel streel). Considering the entire project budget, the saving of even one dowel per joint will lead to significant overall cost savings. As long as these cost savings do not negatively affect the pavement performance, these cost savings could help highway agencies use their limited budgets more efficiently. In response, the Florida Department of Transportation (FDOT) implemented a pilot project on SR5 in Volusia County in 1988 to evaluate the performance of two different dowel bar arrangements (i.e., standard and special dowel arrangements) under real traffic and environmental conditions. The special dowel bar arrangement consisted of three dowels spaced with 304.8 mm (12 in) only within each wheel path. The standard dowel bar arrangement included dowels spaced with 304.8 mm (12 in) within the entire slab width. Crack surveys, faulting measurements, and falling weight deflectometer (FWD) measurements were conducted in the years of 1989, 1992, 1998, 2005, and 2015. Based on the results analyzed, both dowel bar arrangements performed very well, and lasted longer than the design life of 28 years.
Although previous research reported that the pavement with a special dowel bar arrangement shows a good filed performance, there is a need to study how the reduced number of dowel bars achieves the appropriate load transfer across the joints in terms of the concrete bearing stress, dowel shear forces, and slab deflection. Also, a better understanding regarding the dowel bar load transfer mechanism may help to improve the dowel bar design and construction procedures. In this study, a threedimensional (3D) finiteelement (FE) model was developed to simulate the dowel bar load transfer under FWD loads. Analytical FWD deflections calculated were compared with those actually measured from FWD tests to validate the FE model developed.
1.2 Objectives and Scope

Identify the effect of different dowel bar arrangements on the bearing stresses in the surrounding concrete, shear stress in dowel bar, and deflections under the critical loading condition.

Evaluate the effect of the base layer (i.e., base modulus) on the doweljoint behavior for different dowel bar arrangements.

Evaluate the effect of different dowel bar arrangements on field performance under actual traffic and environmental conditions in Florida.
2 Overview of Dowel Bar Application
Recommended dowel bar diameter versus pavement slab thickness.
Slab thickness  203  216  229  241  254  267  279  292  305  318 

Florida  –  25  32  32  32  32  38  38  38  38 
California  32  38  38  38  38  38  38  38  38  38 
Iowa  32  32  32  32  38  38  38  38  38  38 
Illinois  38  38  38  38  38  38  38  38  38  38 
Indiana  25  25  32  32  32  32  32  32  32  38 
Michigan  32  32  32  32  32  32  32  38  38  38 
Minnesota  32  32  32  32  32  38  38  38  38  38 
Missouri  32  32  32  32  32  38  38  38  38  38 
North Dakota  32  32  32  32  32  38  38  38  38  38 
Ohio  25  32  32  32  32  38  38  38  38  38 
Texas  25  –  29  –  32  –  35  –  38  – 
Wisconsin  32  32  32  32  38  38  38  38  38  38 
Specification of dowel bar misalignment tolerance.
States  Maximum rotation (mm)  Vertical translation (mm)  Longitudinal translation (mm) 

Florida  13  25  50 
Illinois  5  –  – 
Indiana  10  –  – 
Iowa  6  –  – 
Kansas  10  1/10 of slab thickness  – 
Minnesota  6  –  – 
Nebraska  6  –  – 
Georgia  14  –  – 
North Carolina  10  –  – 
South Carolina  14  20  76 
When concrete slabs are subjected to loads, bearing stresses and deflection are mainly affected by the spacing of dowel bars. Decreased dowel bar spacing results in the reduction in bearing stresses and deflection. However, if dowel bar spacing decreases to less than 203 mm (8 in), a horizontal plane of weakness in the concrete slab at the joint face will occur. On the contrary, the increased dowel bar spacing leads to excessive bearing stresses and deflection at the joint. Currently, most highway agencies have adopted a 305 mm (12 in) spacing requirement, which also depends on the slab thickness and subgrade conditions.
3 FullScale Field Performance Evaluation
3.1 Project Description
The Florida Department of Transportation (FDOT) implemented a pilot project on SR5 in Volusia County, Florida in 1988 to evaluate the performance of two different dowel bar arrangements (i.e., standard and special dowel arrangements) under real traffic and environmental conditions. It is noted that the annual daily truck traffic was reported to 15,910 in 1997. The project is composed of three sections with slab thicknesses of 152, 178, and 203 mm (6, 7, and 8 in). Each of these sections consists of six 152 m (500 ft) long subsections. The 152 mm (6 in) sections include slabs with 3.7, 4.3, 4.9 m (12, 14, and 16 ft) joint spacing. The 178 mm (7 in) sections include slabs with 4.3, 4.9, and 5.5 m (14, 16, and 18 ft) joint spacing. The 203 mm (8 in) sections include slabs with 4.9, 5.5, and 6.1 m (16, 18, and 20 ft) joint spacing.
3.2 Construction
3.3 Pavement Performance Evaluation
4 Finite Element (FE) Analysis
4.1 FE Model Development
No restraints were considered for the concrete slab to allow for the possible loss of contact due to temperature differentials in the slab by modeling the unbonded interface condition between the concrete slab and the subgrade layer using contact and target elements. The slab contact with the subgrade layer was only retained by the selfweight of the slab. The interface model was also capable of capturing the effect of friction, and a value of 1.5 for coefficient of friction was assumed in the FE model. Also, the surface condition between dowel bar and surrounding slab was also modeled using the contact surface with a value 0.6 for a coefficient of friction. The dowel bar was confined by the slab weight and then was allowed to slide when the force to pull the dowel bar was greater than confined force in the surface of dowel bar.
The mechanical and thermal behaviors of the concrete slab are characterized by its modulus of elasticity, Poisson’s ratio, coefficient of thermal expansion, and density. Also, the subgrade layer and dowel bars were considered as linear elastic materials characterized by their modulus of elasticity and Poisson’s ratio. In particular, the use of a finer mesh for the 3D dowel bar is imperative to accurately capture the dowelsliding, shear force transfer, and bearing stresses in the concrete. In this study, the sliding interface was modeled between concrete and dowel bars in order to effectively simulate the dowel bar movement in consideration of the temperature effect.
Material properties used in the FE model.
Layer  Property  Value 

Concrete  Compressive strength (MPa)  45.5 
Flexural strength (MPa)  5.8  
Modulus of elasticity (GPa)  29.7  
Poisson’s ratio  0.2  
Coefficient of thermal expansion (/ °C)  11.75 × 10^{−6}  
Density (kg/m^{3})  2322  
Dowel bar  Modulus of elasticity (GPa)  200.0 
Poisson’s ratio  0.3  
Diameter of dowel bar (cm)  2.5  
Length of dowel bar (cm)  46.0  
Subgrade  Modulus of elasticity (MPa)  690.0 
Poisson’s ratio  0.35 
4.2 Calibration of FE Model Developed and Determination of Model Parameters
5 FE Analysis Results
Effects of different dowel bar arrangements on deflections and stresses.
Dowel design  Standard  Special  Difference (%) 

Peak corner deflection (mm × 10^{−2})  69.60  72.14  3.8 
Peak edge stress (MPa)  1.97  2.06  4.5 
Bearing stress in surrounding concrete (MPa)  4.53  4.75  5.0 
Peak dowel shear stress (MPa)  7.73  7.74  0.2 
6 Conclusions

Based on the field performance evaluation results, no apparent performance difference was observed between the sections with standard dowel and special dowel arrangements. This matches well with the results obtained from the analytical FE model developed.

No significant changes in pavement structural responses, including the slab stresses and deflections, were identified between two dowel bar arrangements evaluated. This may result in no significant difference in expected performance for the test slabs evaluated.

It was found that the base modulus plays an important role on the doweljoint behavior and stiffer base condition could significantly improve the doweljoint performance.

It was concluded that when the base layer is stiff enough to support the slab deflection and resist erosion (e.g., AC layer), the special dowel bar arrangement (i.e., reduced number of dowel bars only within the wheel paths) could provide similar performance as compared to a standard dowel bar arrangement. This may result in significant cost savings without any negative effects on expected pavement performance.

Future research efforts are recommended to further evaluate the longterm performance of different dowel bar arrangements using dynamic fatigue tests approach.
Declarations
Acknowledgements
The Florida Department of Transportation is gratefully acknowledged for providing the financial support that made this study possible. The authors would like to acknowledge the FDOT’s State Materials Office Pavement Materials Section staff for their assistance with data collection, materials testing, and technical advice.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Authors’ Affiliations
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