The transfer of tensile force from the strand to a compressive force in the concrete is accomplished over a bonded length, termed the transfer length, along which the steel stress increases from zero at the free end of the strand to the full initial prestress at the end of the transfer length.7–10 The magnitude of this transfer length is considered to
be affected by initial prestress, strand diameter, strand surface condition, concrete compressive strength, and method of strand release.6–8,11 Complete agreement has not
been reached concerning the contribution of each of these factors. Only strand diameter and effective prestress are included in the ACI 318-11 and American Association of
State Highway and Transportation Officials’ (AASHTO’s) LRFD Bridge Design Specification12 expression for transfer length lt (Eq. [1]).