ABSTRACT
Cable stays may be sensitive to water ingress in the lower anchorage, which may induce severe corrosion. The corrosion may occur even though strands are protected by a multi-barrier system comprising main HDPE cable tubes, strand individual HDPE sheathing and waxing and galvanization of strand wires. The reason for this is that parallel strand systems are anchored by wedges inducing a wound in the zinc, which with water ingress may initiate a corrosion process increasing the risk of strand failure in time. Motivated by this, this paper presents firstly the details of the ultrasonic testing method (Uscan) used to classify strand wires of cable stays according to different levels of corrosion defects. The rates of false positives and false negatives of the techniques are quantified for the case study presented, given that some cable stays where replaced and were subject to exhaustive testing and visual inspection. Then, data from 10 years of ultrasonic tests are used to explore correlation patterns in corrosion levels at different scales including strand, cable stays and system of stays in a bridge. This has led to an improved understanding of the corrosion condition of the considered cable stays. A histogram technique is presented as means of a systematic data quality check to compare data from different testing campaigns. A regression model to predict the tensile resistance of a strand/cable stay based on the condition classification from the ultrasonic tests is presented. Model parameters quantify the resistance associated with different wire conditions. The results from different ultrasonic testing campaigns in time can be used to estimate the resistance of the cable stays via the proposed model. This, supplemented with design loads and other sources of information, can be used to inform strategies for managing deteriorating cable stays. Finally, lessons learnt from the present case-study and recommendations to manage corroding cable stays are discussed.
