Theoretical Analysis of Transfer Lengths in Pretensioned Prestressed Concrete Members

The realistic design of pretensioned prestressed concrete members requires adequate determination of transfer length for prestress forces. The purpose of the present paper is to propose a rational theory, which can evaluate the transfer lengths realistically for arbitrary designed pretensioned members. The theory considers the prestressing steel as a solid cylinder and the surrounding concrete as a hollow cylinder. The compatibility condition is then imposed at the steel—concrete interface with an appropriate equilibrium equation. The possible cracking of surrounding concrete in a radial direction due to expansive pressure after prestress transfer has been considered by employing an appropriate tensile stress—crack width relation. The equilibrium equations are solved for each successive segment in longitudinal direction and the strain buildup curves from the end of pretensioned members are obtained, which provides the basis for the determination of transfer length. Comprehensive tests were conducted to measure the transfer lengths for various design variables, including the concrete strength, strand diameter, cover thickness, and strand spacing. The measured values of transfer lengths were compared with the calculated ones and the comparison indicates that the theoretical prediction exhibits good correlation with test data. The proposed theory allows more realistic prediction of transfer lengths for rational design of actual pretensioned prestressed concrete members.