End Zone Reinforcement for Pretensioned Concrete Girders
In this study, a literature review was conducted to establish the background of current specifications and to evaluate the applicability of various theories and methods for design of end zone reinforcement. Analytical methods reviewed in this paper include finite element analysis, strut- and-tie modeling, and the Gergely-Sozen equivalent beam method. Previous experimental work combined with work conducted as part of this study were used to correlate between various theoretical and experimental results. This paper illustrates that no single theoretical method adequately represents the complex behavior at the end of a pretensioned concrete member. A general semi-empirical design procedure is proposed here. It is based on theoretical behavior and experimental observation. Standard reinforcement details are given. The proposed procedure could result in reduction in the congestion of reinforcement while maintaining acceptable crack control at the member end. Application of the proposed procedure to highly pretensioned bridge girders is demonstrated.
Strand debonding for pretensioned bridge girders to control end cracks
Characteristic cracks occur at prestressed bridge girder ends during prestress release due to the transfer of the prestress force to the concrete. This research investigated the quantitative and qualitative impact of strand debonding on cracking through nonlinear finite element analysis (FEA) and plant observations. The analysis included plastic behavior of concrete and stress redistribution after tension induced cracking. Prestressed bulb tee girders, 54, 72, and 82 in. (1372, 1829, 2083 mm) deep, were analyzed with 25, 35, and 50% of the strands debonded at the girder end. The tensile strains were used to judge cracking, and were compared with cases that had no debonding. The results showed that 25% debonding can completely eliminate the excessive concrete tension strains associated with cracks in critical locations. For cracks in other locations, related strains were considerably reduced with 25 to 35% debonding, and eliminated with 50% debonding. The selection of the strands to be debonded significantly impacts cracking. Recommendations on debonding strands and desirable bonded strand patterns are presented.
ANCHORAGE ZONE REINFORCEMENT FOR POST-TENSIONED CONCRETE GIRDERS
This report presents the results of an extensive study of design requirements for anchorage zone reinforcement for post-tensioned concrete girders. The study included a literature review, survey of current state of the art based on an extensive user survey, and a substantial number of physical tests to verify proposed design approaches. Major variables included various anchorage hardware types and degrees of confinement, various types of end anchorage applications (concentric, eccentric, inclined, curved, multiple and with end reactions or lateral post-tensioning), slab anchorages, intermediate anchorages (pocket, blister, and ribs), and diaphragm anchorages. Analytical approaches included strut-and-tie models, finite element analysis, and approximate equations. Correlation between analytical approaches and experimental results was excellent. The report includes recommended design and construction specifications suitable for inclusion in the AASHTO bridge specifications.