Challenges of water ingress into bridge cable systems

Experience with the operation and maintenance of cable-borne bridges of various ages over the last 20 years shows that water ingress into steel cable systems often occurs and causes a high risk of serious corrosion that may lead to traffic restrictions, extraordinary inspection and maintenance costs and, in the worst case, bridge closures. Examples of such experience cover suspension bridges as well as cable-stayed bridges in the USA, UK, Germany, France, Argentina, Sweden, Norway, Denmark and many other countries. The problem of water ingress is particularly critical as inspections for corrosion in cable systems are difficult to carry out and early warnings difficult to obtain.
Water ingress into a cable system means that there is a significant risk of steel corrosion even with precautions such as the use of galvanization and HDPE coating of cable wires. Although cable system designs generally comprise multiple barriers against corrosion, there is often a weak link in the design. This, combined with an unintended outcome in the construction phase or inadequate maintenance, may allow water to start accumulating and lead to corrosion.
This paper will explain and discuss cases from main cable and cable-stay systems and point out the water ingress modes and their causes for main cable systems and different cable-stay systems. Based on that, the paper discusses the weaknesses of the different steel cable concepts and different mitigations. The discussion also includes the mitigation of the water ingress problem through the use of dehumidification. This concept has been successfully used for the main cables of suspension bridges for more than 15 years. Considering the number of known problems with water in cable stays, the paper also contemplates the possibility of using dehumidification for cable-stayed bridges as a way of handling the large number of existing cable-stayed bridges.