Vulnerability and Robustness of Corroded Large-Span Cable-Stayed Bridges under Marine Environment

The vulnerability and robustness of in-service cable-stayed bridges under a marine atmospheric environment is studied based on several specific considerations in modeling corrosion-induced damage in cables. With the limited test data available, the corrosion model for cables exposed to marine environmental conditions is modified to reflect the coupled effect of cable in-service stress level with an assumed probability distribution of corrosion of steel wires along a cross section. To ideally capture the dynamic effect caused by corrosion-induced rupture, the complete sudden element removal strategy is simulated by using computer software developed by the Pacific Earthquake Engineering Research (PEER) Center. In the assessment of bridge vulnerability, the stress transfer coefficient is introduced as well as normalized corrosive section area to reflect the major propagation of stress within adjacent cables. The so-called performance index combined with the definition of critical failed pairs of corroded cables is applied to evaluate the influence of corrosion on the robustness of cable-stayed bridges. The results from a case study on a 1,088-m span cable-stayed bridge reveal that the optimal geometrical configuration of a bridge deck would be possibly adversely altered if corrosion is severe. The bending moment at the bottom of the towers exhibits a considerable increase of 171.6% after 20 years of corrosion. In any corrosion case, all the vulnerable cables are distributed near the towers. Among five regions defined in the analysis of robustness, cables in the side span, i.e., Region 4, are most robust in any case, although this region is most sensitive to preliminary corrosion. Comparatively, cables located within the $1/4$th main span and main towers, i.e., Regions 2 and 3, are not only sensitive to initial corrosion-induced damage but also more likely to reach their allowable stress level.