United States Department of Transportation
i
Designing for Deck Stress Over Precast Panels in Negative Moment Regions
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2021-12-01
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[PDF-17.53 MB]
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Edition:Technical Report (Jan 2016-Dec 2019)
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Abstract:With increases in the use of precast concrete panels (PCPs) in Texas bridges, ensuring acceptable deck cracking behavior is of paramount importance to avoid long-term maintenance problems. The purpose of this study is to understand the cracking behavior of reinforced concrete bridge decks with precast concrete panels in the negative moment regions of continuous girders under service loading and to develop comprehensive guidelines for reinforcing steel details in the bridge decks in the negative moment regions of bridges utilizing PCPs. A major focus of the study is the influence of the reinforcing details on the control of deck crack width. Four concrete bridges were monitored during the construction period. Texas Department of Transportation (TxDOT) Implementation Project 5-6909-01 is focused on the instrumentation and monitoring of the continuous steel bridge in Bastrop to further evaluate deck reinforcement requirements. Concrete early-age shrinkage is the dominant reason for deck cracking. Increasing reinforcement ratio and decreasing rebar spacing showed some benefits. Through large-scale laboratory testing on composite Tub girders, the surface crack widths generally matched the predictions from the American Association of State Highway and Transportation Officials (AASHTO) crack width equation correlating with the maximum rebar stress, and concrete tension stiffening effect was also observed in the concrete specimen direct tensile tests. The numerical parametric studies confirmed that the deck reinforcement ratio is the critical factor for the maximum rebar stress. Finally, a design procedure is proposed for the longitudinal deck reinforcement in the negative moment regions. In most cases, using #4 bars spaced at 9-in. plus #5 bars spaced at 9-in. (ρ=1.1%) or #5 bars spaced at 6-in.(ρ=1.1%) reinforcing steel in the top mat, the maximum rebar stress can be limited to no more than 36-ksi under Service I load combination, and crack width can be limited to approximate 0.012 in.
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