Since its construction in 1964 the Forth Road Bridge has undergone continuous maintenance and upgrading. During a routine inspection in 1998 it was recorded that a dangerously high level of corrosion was evident on the main load-bearing wire hangers that supported the bridge.
When this inspection report was presented to the Scottish Office it was agreed that this problem required immediate attention. At this point a resident engineer was appointed to supervise and co-ordinate the maintenance and upgrading project.
Millar Callaghan’s C.S.W.I.P. inspector was then invited to become part of the management team who were responsible for the front line supervision of the contractors involved on the project.
The biggest engineering problem in this contact was that each wire hanger supported a percentage load of the whole bridge. This load had to be calculated and transferred onto temporary hangers to ensure that the bridge could operate normally while the new hangers were being prepared and installed.
The contractor presented the management team with a method statement showing the order in which the various steps of the hanger replacement would take place and, after several site meetings between the resident engineers and the contractors, the project began.
As one of the resident engineering teams, our role was to witness every load transfer, calculate the load, record it and make sure these results were used to re-install the new hangers so the bridge theoretically sat back in exactly the same position. Once the old hangers were removed the existing steel was fully tested and any welding and painting repairs were carried out prior to the installation of the new hangers.
