Probabilistic calibration of design resistance models for the anchorage length of prestressing strands considering model uncertainty

• Model uncertainty for anchorage length models are estimated; • fib 2020 and 2nd generation Eurocode formulations are analyzed; • experimental results from 1980s to 1990s may be affected by altered strand surface conditions; • a new target reliability coefficient has been proposed. This study investigates the reliability and the model uncertainty of the anchorage length resistance models proposed in the 2nd generation Eurocode 2 and fib Model Code 2020. First, the two resistance models and their safety format are presented and discussed. Then, the probability distribution of the model uncertainty is estimated comparing the model predictions with a large set of flexural tests collected from the scientific literature. According to the results, the prestress release method and the strand surface conditions are the two variables affecting most the model uncertainty. Furthermore, it is demonstrated that anchorage lengths predicted with fib Model Code 2020 exceed the expected target level of reliability and they could be reduced, particularly for gradual prestress release. Conversely, anchorage lengths calculated according to the 2nd generation Eurocode 2 in case of sudden prestress release need to be increased to guarantee the expected level of reliability. For the same code, no significant changes are necessary in case of gradual prestress release.