Measured Transfer Lengths of 0.7 in. (17.8 mm) Strands for Pretensioned Beams

[EN] The use of 0.7 in. (17.8 mm), Grade 270 (1860) prestressing strands has advantages over 0.5 and 0.6 in. (12.7 and 15.22 mm) strands. This study provides design guidelines for estimating transfer length of 0.7 in. (17.8 mm) strands. Sixteen pretensioned concrete beams using a single prestressing strand were fabricated with conventional concrete and self-consolidating concrete. The concrete strengths at 1 day ranged from 5.9 to 9.2 ksi (40.7 to 63.4 MPa). Transfer lengths were determined using concrete surface strains along with the Average Maximum Strain Method. Initial strand end slips were also measured for predicting transfer length at release using an empirical formula. Experimental results indicated ACI 318 and AASHTO specifications are applicable for estimating transfer length of 0.7 in. (17.8 mm) strands at release and at 28 days. The results also showed that a coefficient of 2.32 was the most appropriate value for estimating transfer lengths at release from initial strand end slips.