Bond Behaviour of Grouted Strands at Elevated Temperatures Considering Tendon Eccentricity

Tendon eccentricity produces non-uniform grout thickness within ducts in bonded post-tensioned concrete structures. Its implications for bond behaviour were investigated through 53 pull-out tests on mono- and triple-strand tendons embedded in grouted corrugated steel ducts within concrete cylinders. Eccentricity was varied at ambient temperature, whereas tests during heating and after cooling used the maximum eccentricity for each tendon configuration. The programme covered 20–600 °C and included comparisons of water cooling for mono-strand specimens and helical confinement for triple-strand specimens. Increasing eccentricity reduced ambient-temperature bond strength. Bond strength and initial stiffness decreased with temperature, with the fitted relationships indicating reductions to half their ambient-temperature values at approximately 242 °C and 118 °C, respectively. Bond strength recovered slightly after cooling, and water- and air-cooled mono-strand specimens showed similar responses under the tested conditions. For specimens classified as having medium confinement, post-peak residual bond strength averaged approximately 70% of the corresponding characteristic bond strength, while specimens exhibiting through splitting retained little residual resistance. Helical reinforcement improved the post-peak response of triple-strand tendons, although its contribution to bond strength was limited at 100–300 °C when concrete cover spalling occurred. The results were used to recalibrate a trilinear bond–slip model for the observed confinement conditions.