Implementation of 0.7 in. Diameter Strands in Prestressed Concrete Girders.

摘要

For several years, 0.7 in. diameter strands have been successfully used in cable bridges and for mining applications. Using these large diameter strands at 2 in. by 2 in. spacing in pretensioned concrete girders results in approximately 35% increase in the prestressing force compared to the same number of 0.6 in. diameter strands and 92% increase in the prestressing force compared to the same number of 0.5 in. diameter strands. This will, consequently, allow for longer spans, shallower structural depth, and/or wider girder spacing in bridge construction. In this paper, the application of 0.7 in. diameter strands at 2 in. by 2 in. spacing to the Oxford South Bridge in Nebraska is presented. Twenty-six strand samples were tested to evaluate the breaking strength, yield strength, and modulus of elasticity of 0.7 in. diameter strands. Test results indicated that the tested strands meet the requirements of the ASTM A416-07. Also, transfer length measurements were taken at three different locations on two prestressed concrete girders at release and after 14 days using DEMEC gauges. Measurements indicated that the transfer length of 0.7 in. diameter strands can be conservatively estimated using the AASHTO LRFD Bridge Design Specifications. All fabricated girders were monitored for end zone cracking and camber growth and were found in compliance with current production tolerances, as specified by PCI and the Nebraska Department of Roads.