Forth Road Bridge – maintenance challenges

Abstract

Forth Road Bridge is a suspension bridge with a main span of 1006 metres and side spans of some 408 metres. Approach viaducts to the north and south bring the total length of the structure to just under 2500 metres. The bridge was opened in 1964 and traffic has grown significantly from 4 million to 24 million vehicles using the bridge each year. All work carried out on the bridge has to be done under a regime of overnight or limited weekend carriageway or lane closures to minimise delays to users on this important strategic and commuter route. Following a recent internal inspection of the main cables, significant corrosion was found leading to remedial works being planned. The inspection and remedial works are described elsewhere. This paper deals with the other major projects on the bridge. Several large projects to strengthen and improve the structure, and replace major components have already been carried out. These have included strengthening the main towers to allow for increased live loading; constructing pier defences at the main towers to withstand shipping impact; replacement of the hangers and replacement of underdeck access gantries and runway beams. Several more significant projects are planned over the next 15 year period. These will include strengthening the suspended span deck truss; replacing the main suspended span and approach viaduct deck joints; replacing the bearings on the approach viaducts and parapet replacement. In addition, major maintenance projects such as waterproofing and resurfacing the carriageways and painting the suspended span truss, the approach viaduct box girders and the main towers will also be carried out.