Bottom Flange Confinement Reinforcement in Precast Prestressed Concrete Bridge Girders
Publication: Journal of Bridge Engineering
Volume 17, Issue 4
Abstract
The AASHTO standard bridge specifications require that nominal reinforcement should be placed to enclose prestressing steel at girder ends for at least a distance equal to the girder’s height. The AASHTO LRFD bridge specifications state that the minimum requirements for this confinement reinforcement is No. 10 (#3) bars at a maximum spacing of 150 mm (6 in.) for at least 1.5 times the girder’s height. Neither standard nor LRFD specifications justify the need for such reinforcement. The main objective of this study is to investigate the effect of confinement reinforcement on the performance of prestressed concrete bridge girders. Of particular interest is the effect on transfer and development length of prestressing steel and on the shear capacity of prestressed girders. The experimental investigation includes testing the flexural and shear capacities of 610 mm (24 in.) deep T-girders and 1,100 mm (43.3 in.) I-girders. The results indicate that (1) neither the amount or distribution of confinement reinforcement has a significant effect on the transfer length of prestress strands; (2) at the AASHTO calculated development length, the amount of confinement reinforcement does not have significant impact on either the nominal flexural capacity of bridge girders or bond capacity of the prestressing steel, however, the distribution of confinement reinforcement along the entire length of the girder results in improved ductility and reduced cracking under extreme loading conditions; and (3) confinement reinforcement improves the anchorage of strands at girder ends, and consequently, the shear capacity of prestressed girders.
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Acknowledgments
We thank the Nebraska Department of Roads (NDOR) for their financial and technical support of this project. We are also very thankful for Coreslab Structures, Inc., (Omaha, NE), Ivy Steel & Wire (St. Joseph, MO), and InSteel Industries Inc. (Mt. Airy, NC) for their material donation and technical support. Special acknowledgment goes to all the students and technicians who participated in various tasks of the project.
References
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© 2012. American Society of Civil Engineers.
History
Received: Aug 17, 2010
Accepted: Jul 14, 2011
Published online: Jun 15, 2012
Published in print: Jul 1, 2012
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