Spacing requirements of 0.7 in. (18 mm) diameter prestressing strands

Abstract

[EN] The use of 0.7 in. (18 mm) diameter strands for pretensioned concrete girders is advantageous when increasing the flexural capacity and extending girder spans. The current codes have no design guidelines for predicting transfer length, development length, and minimum strand spacing for this greater-diameter strand. This study measures transfer and development lengths and evaluates the applicability of using a strand spacing of 2.0 in. (51 mm) for 16 pretensioned concrete beams with 0.7 in. diameter strands. These beams were fabricated with high-strength, conventional concrete or self-consolidating concrete. The Standard Test Method for Evaluating Bond of Seven-Wire Steel Prestressing Strand (ASTM A1081) was used to quantify the strand surface conditions. The experimental results indicate that the current ACI 318-14 and AASHTO LRFD specifications overestimate the measured transfer and development lengths for the beams. Transfer and development lengths of the beams containing two strands placed at 2.0 in. spacing were equal to or slightly greater than those of the beams containing one strand. Finally, the concrete region around the strands showed no sign of cracking.