Influence of knowledge uncertainties on the safety assessment of existing post-tensioned concrete bridges

The assessment of existing bridges constitutes a serious challenge for the researchers since their safety evaluation is a complex task due to several sources of uncertainty affecting the knowledge process. In particular, a high level of uncertainties may arise in the case of prestressing systems requiring special investigation strategies and experimental technologies. The paper aims to investigate how the knowledge uncertainties influence the safety assessment of existing post-tensioned bridges using the semi-probabilistic approach. Uncertainties related to the knowledge process are described considering the number of tests, the confidence level assumed for the estimation of the problem parameters, and the measurement errors of in-situ tests. Results concerning a typical post-tensioned bridge are reported and the variability of the outcomes is discussed and compared with a reference case of "perfect knowledge". The main results of the study confirm the general robustness of the semi-probabilistic Eurocodes safety format and provide an overview of dispersion due to different choices regarding the number of tests and confidence level. The measurement errors may lead to significant underestimation of the computed structural capacity with respect to the reference one, up to -40% of the reference case considering standard confidence levels.