Contractors have installed a suspended gantry which enables engineers to repair and maintain the steel deck of the Forth Bridge without closing it to rail traffic.
Balfour Beatty is to carrying out works to repair damage caused by years of heavy rail freight traffic crossing the 128-year-old bridge.
The 2.5km long balanced cantilever structure between South and North Queensferry has been in constant use since it first opened as the world’s first steel bridge in March 1890.
The gantry hangs 46m above the Firth of Forth and will remain insitu for the next two years to facilitate the repairs to steel work of the trough deck area of the central suspended span.
The design of the gantry allows the team to make repairs from below, eliminating the need to disrupt the 200 train services a day crossing the structure.
“This work will focus on repairs to the trough deck area of the suspended span,” said Network Rail asset engineer Jamie Mclaren. “This section of the bridge is underneath the running lines and is part of a wider maintenance programme to fix similar defects across the whole length of the Forth Bridge over the next few years.
“Steelwork repairs to these areas will address historic deterioration of the steel deck caused by various changes in track profile and heavy freight traffic which no longer runs across the bridge”.
Balfour Beatty is the lead contractor for the repair and maintenance work. Network Rail currently spends around £1M per year on regular inspections, maintenance and repairs to the structure.
Balfour was also the primary contractor for the bridge’s £140M 10 year restoration project which ended in 2011. This focused on the critical structural elements of the bridge, with the work involving steel repairs and painting.
The aim of this work was to halt steel corrosion, maintain the integrity of the structure and apply a coating system which would reduce the need for repainining and general maintenance.
Balfour Beatty construction superintendent Colin Hardie said work on the structure was a logistical challenge.
“The gantry itself is large structure, so getting it out onto the water then raised up to deck level was a major logistical challenge,” he said. “Now it’s in place, we can move it gradually along the underside of the suspended span as steel repairs are completed.”
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