16.10: Challenges with water ingress in bridge cable systems

Abstract

ABSTRACTExperiences over the last 20 years with operation and maintenance of cable borne bridges of various ages shows that water ingress in steel cable systems often occurs and causes a large risk of serious corrosion with may lead to restriction in traffic, extra ordinary inspection and maintenance costs and in worst case bridge closure. Examples of such experiences cover suspension bridges as well as cable stay bridges in USA, UK, Germany, France, Argentina, Sweden, Norway, Denmark and many other countries. The problem with 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 by 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 stays systems. Based hereupon, 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 by use of dehumidification. For main cables of suspension bridges, the concept has been in operation for more than 15 years with success. Considering the number of known problems with water in cable stays, the paper also contemplates on the possibility of using dehumidification for cable stay bridges as a way of handling the large amount of existing cable stay bridges.