Bond Modelling for the Assessment of Transmission Length in Prestressed-Concrete Members

Transmission of the prestressing force to concrete by prestressing tendons is a topic of discussion within the fib Task Group 2.5: Bond and Material Models. Particularly, the extensive use of pretensioned prestressed-concrete (PC) requires adequate knowledge of bond development at the steel–concrete interface after prestress release. The transmission length, representing the distance from the free-end of the beam necessary to transmit the fully effective prestressing-force to the surrounding concrete, is a design parameter of paramount importance for PC members detailing. This contribution presents the analytical modelling of the transmission length based on the thick-walled cylinders (TWC) theory, considering anisotropic behaviour of the concrete. To derive the optimal friction coefficient between steel and concrete, the theoretical model has been calibrated according to an experimental database of transmission lengths collected from the literature, encompassing 130 data points from 7 different campaigns. Additionally, local behaviour has been analysed by assessing radial cracking and bond stress development along the transmission length.