Severn Bridge – Recent Assessment of Main Suspension Cables

The Severn Bridge was built in 1966 and was a pioneer of streamlined box girder deck construction. An investigation of the capacity of the suspension cables was commissioned in response to corrosion concerns brought about by inspections of similar suspension bridges. The first intrusive inspection found corrosion of cables resulting in reduced strength. In response, acoustic monitoring and an enhanced dry air injection system were installed. A corrosion-based deterioration model was also developed. An initial assessment of the cable based was then carried out. A second intrusive inspection was then carried out to allow a more realistic assessment of the conditions of the cables to be made and has also been used to calibrate and update the deterioration model. This has shown that the loss of strength of the cables is no worse that the calculated capacity undertaken following the initial examination and the current system of protection has stabilised the condition of the cable.