Reliability Assessment and Calibration of Code Provisions for Bond of Prestressing Tendons

Numerous daily verifications in structural concrete engineering are based on the assumption of "perfect bond". Although crucial, bond of prestressing tendons has not been as thoroughly investigated in the literature as the bond of conventional bars. Thus, this dissertation aims to evaluate and discuss the potential impact of the changes in strand production process that took place during the 1980s-1990s on the bond of prestressing tendons, and to assess the statistical uncertainties associated with the application of bond models. As a concluding result of this dissertation, newly adjusted and statistically calibrated prestressing bond formulations are proposed. These formulations are completely consistent with the partial safety factor verification format outlined in the design codes and can be easily used in daily engineering practice. To this end, in this dissertation, a critical comparison of the bond models available in the most recent editions of the main design codes is provided. Subsequently, a probabilistic analysis of the transmission and anchorage length models introduced in the 2nd generation Eurocode 2 and in fib Model Code 2020 is performed. Ultimately, based on the findings, novel probabilistic coefficients for the analyzed bond lengths are introduced. These coefficients have been calibrated by adopting a large dataset of experimental results and validated with the First-Order Reliability Method for a wide range of design scenarios. In addition, these coefficients have been optimized to be completely consistent with the partial safety factor approach, minimizing deviation from the prescribed target reliability. Finally, design verifications where prestressing bond lengths are required are examined, emphasizing the advantages and implications of implementing the proposed coefficients in the design practice.