Forth Road Bridge main cables: replacement/augmentation study

The 1800 m long suspended structure of the Forth Road Bridge spans the Firth of Forth in Scotland. It forms an integral part of the roads network, carrying in excess of 24 million vehicles each year. Since its opening in 1964, the bridge has received a high level of continuous maintenance and, when required, retrofitting to enhance the capacity of the structure. In 2004, as part of this maintenance and inspection regime, the Forth Estuary Transport Authority (FETA) undertook the first internal inspection of a main cable of a suspension bridge in the UK. This inspection revealed significant corrosion in the wires forming the cable, and a subsequent inspection in 2008 confirmed these findings. To combat progression of the corrosion, the authority retrofitted dehumidification systems on the main cables, and acoustic monitoring has been fitted to monitor wire breaks within the cables. As a precautionary measure, FETA also commissioned a study into the feasibility of augmenting or replacing the bridge's main cables. This paper outlines the processes undertaken in this study, the options for undertaking the works and the conclusions reached to date.