Lifetime predictions of prestressed concrete bridges—Evaluating parameters of relevance using Sobol' indices

The residual structural lifetime of concrete bridges is often limited by fatigue of the prestressing steel. In practice, numerical calculations of the structure are combined with Miner's rule—based on load frequencies and stress amplitudes—to estimate the damage. Thereby, various parameters must be accounted for whereof a few are actually relevant. Structural monitoring is valuable to increase the accuracy of lifetime predictions, but usually experts choose the right parameters on experience only. A more objective assessment can be reached by sensitivity analysis. A powerful method is provided by Sobol's variance-based indices. They quantify the influence of a single parameter's variance on the model's total variance and account for interactions in nonlinear models, too. Exemplified on a reference structure, sensitivity indices are determined. Meanwhile specific characteristics like the nonlinear behavior of concrete after cracking are considered. In this case, the key elements of lifetime prediction turn out to be the time-dependent losses of prestress and the traffic loads.