Civil Engineering Association

Evaluation of Longitudinal Joint Tie Bar System

An adequate longitudinal joint tie bar system is essential in the overall performance of concrete pavement. Excessive longitudinal joint openings are believed to be caused by either inadequate tie bar size or spacing or improper tie bar installation. If designed and installed properly, tie bars prevent the joints from opening and consequently improve load transfer efficiency between slabs and between slabs and shoulders, resulting in increased load carrying capacity. This study evaluated the longitudinal joint tie bar system currently used by CDOT, examining the criteria for proper use of tie bars and determining the maximum number of lanes that can be tied together without negatively impacting the concrete pavement structure. An improved mechanistic-empirical tie bar design method was developed. Tie bar design tables with recommended bar size and spacing were provided for each combination of pavement base types, CDOT concrete mixes, and weather stations. Field studies were conducted to investigate longitudinal joint performance and further evaluate the impact of factors related to design and construction practices. The experimental plan for this round of testing included the evaluation of tie bar alignment, measurement of joint load transfer, and measurement of relative slab movement at the joints. In addition, CDOT’s current specifications and practices related to longitudinal joint construction and tie bar design and placement were compared with those of other state agencies. Field testing results revealed that the measured joint openings at some tied longitudinal joints were in the typical range of non-tied slabs, implying that some tied joints performed as poorly as non-tied slabs. The results indicate the possibility of tie bar failure due to loss of concrete-steel bonding or yielding of tie bar steel. Another key finding was the possible impact of tie bar misalignment or misplacement on poor longitudinal joint performance. Testing indicated that the measured joint openings were wider when the tie bars did not connect to the other side of the joint, or when the embedment lengths were inadequate. On the other hand, tie bars with adequate embedment length on both sides of the joint, even when misaligned, appear to hold the joint tight. CDOT should adopt the mechanistic-empirical tie bar design procedure developed in this study. The research team recommends that CDOT conduct more rigorous experimental and field testing covering various base material types and concrete mixtures to obtain Colorado-specific model parameters for implementation.