United States Department of Transportation
i
Evaluation of longitudinal joint tie bar system.
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2011-09-01
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[PDF-1.72 MB]
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Abstract:"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.
Implementation
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."
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