Implementation of 0.7 in. diameter strands at 2.0 × 2.0 in. spacing in pretensioned bridge girders.

Use of 0.7 in. (18 mm) diameter strands at 2 × 2 in. (50 × 50 mm) spacing in pretensioned concrete girders results in an approximately 35% increase in the prestressing force compared with the same number of 0.6 in. (15 mm) strands and a 92% increase in the prestressing force compared with the same number of 0.5 in. (13 mm) strands, allowing for longer spans, shallower depths, and/or wider girder spacing. This paper presents the application of 0.7 in. (18 mm) diameter strands at 2 × 2 in. (50 × 50 mm) spacing to the Oxford South Bridge in Oxford, Neb. Twenty-six strand samples were tested for breaking strength, yield strength, and modulus of elasticity. The strands met the requirements of ASTM A416-07.Transfer lengths were measured at three locations on two girders at release and after 14 days. Measurements indicated that the transfer length of 0.7 in. diameter strands can be conservatively estimated using the AASHTO LRFD Bridge Design Specifications. All 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. [ABSTRACT FROM AUTHOR]