Measured Transfer Lengths of 0.5 and 0.6 in. Strands in Pretensioned Concrete

Transfer lengths were measured for both 0.5 and 0.6 in. (12.7 and 15.2 mm) diameter strands for a wide variety of research variables that included strand spacing, debonding strand, confining reinforcement, number of strands per specimen and size and shape of the cross section. Overall, the test results indicate that the transfer bond characteristics for 0.6 in. (15.2 mm) strands are very similar to the bond behavior for 0.5 in. (12.7 mm) strands. Furthermore, average measured transfer lengths for both sizes of strand are marginally predicted by current AASHTO and ACI Code provisions. These results clearly demonstrate that 0.6 in. (15.2 mm) strands can be safely employed in pretensioned concrete members with spacings of 2 in. (50.8 mm). However, the ranges of measured transfer lengths clearly indicate that a significant proportion of actual measured transfer lengths exceed the current design recommendations of either 50d b or f se d b /3. Therefore, to incorporate a more consistent level of safety, transfer lengths should be approximated by the expression f se d b /2.