Use of 0.7-in.- diameter strands in pretensioned bridge girders

Abstract

For several years, 0.7-in.-diameter (18 mm) prestressing strands have been successfully used in cable bridges. Using these large-diameter strands in pretensioned concrete girders at 2 in. spacing increases prestressing force, allowing for longer spans, shallower structural depth, and wider girder spacing that the more commonly used 0.6-in.-diameter strands. This paper discusses the design and production issues associated with using 0.7-in.-diameter strands in pretensioned concrete bridge girders. Two full-scale I-girders pretensioned using 0.7-in.-diameter strands were fabricated and tested to address production concerns and evaluate transfer length, development length, and end-zone cracking associated with the 0.7-in.-diameter strands. The results indicate that 0.7-in.-diameter strands can be used with no major changes to the current production practices or AASHTO bridge design specifications. The design and construction of the first pretensioned concrete bridge to use 0.7-in.-diameter (18 mm) strands is highlighted.