REDUCED STRAND SPACING IN PRETENSIONED, PRESTRESSED MEMBERS

Pretensioned, prestressed concrete girders are used widely in bridge superstructures in the United States. Predominantly, 0.5-in. (12.7-mm)-diameter prestressing strand is used in these girders at a center-to-center spacing of 2 in. (50.8 mm). This corresponds to the four-strand-diameter center-to-center spacing, which is the American Concrete Institute (ACI) 318-89 minimum requirement for pretensioned, prestressed members. In the past, however, several states have used a center-to-center strand spacing of 1.75 in. (44.5 mm) with success. The purpose of this paper is to report the results of laboratory tests designed to determine if the closer strand spacing has a detrimental effect on prestressed girder performance. Twelve test specimens were cast for the study. The experimental results from this research were compared to results in the literature and the provisions of the ACI Building Code (ACI 318-89). It was concluded that the closer strand spacing has no significant effect on transfer length, development length, or nominal moment capacity.