Service load cracking behavior of reinforced concrete bridge decks




Ge, Xiaomeng

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Precast concrete deck panels (PCPs) are commonly used on simply supported girders. With recent advances on the use of spliced concrete girders and the potential to use PCPs on steel girder systems, the deck reinforcement and cracking behavior in the negative moment regions of continuous girder systems is of interest. However, there is currently inadequate guidance on reinforcing requirements for the cast-in-place portion of bridge decks constructed using PCPs in negative moment regions. Developing appropriate deck reinforcing requirements is critical for ensuring acceptable deck cracking behavior and to avoid long-term maintenance problems. The purpose of this study is to understand the cracking behavior of reinforced concrete bridge decks with PCPs in the negative moment regions of continuous girders under service loading and to develop suitable guidelines for their use in such applications. A major focus of the research is the influence of the reinforcing details on the control of deck crack width. Four concrete bridges were monitored during their construction, during subsequent live-load tests with loaded trucks, and while in-service under traffic loading. The monitoring demonstrated that concrete early-age shrinkage is the dominant reason for deck cracking. The measurements demonstrated the influence of the deck reinforcement ratio and rebar spacing on deck cracking behavior. Large-scale laboratory tests on composite steel tub girders showed that surface crack widths generally matched the predictions from the AASHTO crack width equation correlating with the maximum rebar stress. Additional direct tensile tests were carried out to measure the concrete tension-stiffening effects. Numerical parametric studies were carried out to confirm that the deck reinforcement ratio is the critical factor controlling the maximum rebar stress and therefore controlling crack width. A design procedure is proposed for the longitudinal deck reinforcement in the negative moment regions. This procedure shows that in most cases, providing a reinforcement ratio of 1.0% based upon the thickness of the cast-in- place layer limits the maximum rebar stress to less than 36-ksi (Gr. 60 steel) and maximum crack widths to 0.012 in. under the AASHTO LRFD Service I load combination.


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