Abstract
In unbonded post-tensioning tendons, the coefficient of friction varies from one design
standard to another. This variation is caused by the large number of complex factors that must be
considered in design. These factors include the thickness of lubricant or grease present in the system,
clearance between the strand and the plastic sheath, surface characteristics of the strand and plastic
sheath. In order to determine the effect of these factors a series of friction tests were performed on
two different diameters of strand, namely; 12.7mm and 15.24mm diameters. Through a regression
analysis, it was found that the frictional force decreases with an increase in the thickness of the grease
and that friction increases with an increase in the mass of the strand. The degree of friction was found
to be dependent on the surface characteristics of the strand and plastic sheath, clearance between the
plastic sheath and the strand and the extrusion process of the plastic sheath.