Considerations for Precast Concrete Girder End Regions with Large-Diameter Strands

Le résumé fourni par la source

Strand debonding patterns and release (prestress trans¬fer) practices can result in significant local stresses at prestressed girder ends, which are not accounted for in design. This article presents a numerical and analytic study of various single-webbed prestressed concrete girder shapes for which large amounts of prestressing are necessitated by the use of 0.7 in. (17.8 mm) diame¬ter strands. Shapes with wide bottom flanges are shown to potentially exhibit large stresses that effectively pry, or peel, the portions of the flanges extending from the web away from the web. Such peeling stresses can be mostly mitigated by partially debonding strands in the recommended pattern from the outside in. Simi¬larly, releasing or cutting strands in a uniform manner mitigates peeling stresses. While releasing all strands simultaneously is optimal, it is unlikely to be practical for large prestressed components. For conventional release operations, the results presented in this article indicate that a symmetrical top-down method would not result in significant peeling stress. Moreover, pre¬stressed girder end region detailing requirements aimed at providing adequate flange confinement and strand anchorage at the ultimate limit would be adequate to control peeling stresses, including those resulting from the inadvertent use of a poor release sequence.

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