United States Department of Transportation
i
End-Region Behavior and Shear Strength of Pretensioned Concrete Girders Employing 0.7-in. Diameter Strands
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2018-08-01
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[PDF-17.35 MB]
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Abstract:This report provides an overview of a comprehensive research project at The University of Texas at Austin on the end-region serviceability and shear strength of Texas pretensioned bulb-tee girders (Tx-girders) that employ 0.7-in. diameter strands on a 2- by 2-in. grid. Seven full-scale specimens were fabricated and tested at Ferguson Structural Engineering Laboratory. The detailing for mild-steel reinforcement in four specimens was identical to that currently used in Tx-girders with smaller-diameter strands whereas three girders were fabricated with modified end-region detailing. The specimens were extensively instrumented and monitored for transfer length as well as stresses and cracking within their end-regions at the time of prestress transfer. Greater end-region stresses and greater crack widths were detected in the specimens compared to girders with smaller-diameter strands. However, the greatest crack widths within the girder end regions were generally less than 0.007 in. Moreover, the specimens did not show unusual cracking patterns that trigger new concerns regarding the end-region serviceability of Tx-girders that employ 0.7-in. diameter strands. To investigate their load-carrying capacity and failure mechanisms, the specimens were later subjected to shear-critical loading until failure. Significant strand slip indicating anchorage-zone distress was detected in all specimens prior to reaching the peak applied load. However, widespread yielding of the shear reinforcement was also confirmed in all specimens, and the capacities of all specimens were conservatively estimated using the general method in AASHTO LRFD Bridge Design Specifications. It was also found that adding a cap bar to the bottom flange confinement reinforcement can significantly reduce the strand slip and increase the ultimate strength of the girder. The experimental program was supplemented by an extensive parametric investigation that provided insights into benefits and limitations of using 0.7-in. diameter strands and a series of computational simulations that aimed to shed light into mechanics of prestress transfer, failure modes, and effects of potential changes to end-region reinforcement in Tx-girders with 0.7-in. diameter strands.
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