Experimental Assessment of Factors Affecting Transfer Length

Transfer lengths were measured for 184 transfer zones in 36 plant-cast AASHTO Type I girders prestressed with 0.6 in. (15.2 mm) diameter strands at 2 in. (50 mm) spacing. The influence of concrete compressive strengths ranging from 5700 to 14,700 psi (39 to 101 MPa) was investigated. To represent the full range of strand surface conditions found in practice, the prestressing strand featured either a bright mill finish or a rusted surface condition. Several methods of prestress release were employed. Results indicate that transfer length decreases with increasing concrete strength. Transfer lengths increased significantly during the first few weeks after prestress release. Prestress release method had little effect on the transfer length of bright strands in high-strength concrete. Sudden prestress release, however, resulted in significant increases in rusted strand transfer lengths.