Measurement of Transfer Lengths on Pretensioned Concrete Elements

Abstract

This paper reports an experimental program conducted to measure the transfer lengths (or transmission lengths) of pretensioned seven-wire strands in pretensioned concrete specimens. The primary goals of the research were to investigate the ability of the larger 15.2 mm (0.6 in.) strand to reliably transfer its prestressing forces within a reasonable transfer length, and to evaluate the current design provisions for transfer lengths. Eight specimens were pretensioned with 12.7 mm (0.5 in.) diameter strands and 10 specimens were pretensioned with 15.2 mm (0.6 in.) strands. Experimental results indicate that the larger 15.2 mm (0.6 in.) diameter strands require longer transfer lengths and cause more distress than the smaller 12.7 mm (0.5 in.) strands. However, the tests indicate that 15.2 mm (0.6 in.) strands can be readily employed for pretensioned concrete structures. Additionally, the results demonstrate that current design practice estimating transfer lengths can lead to unsafe designs and that a more reliable expression for transfer lengths should be adopted.