JAPANESE ENGINEERS from Nippon Steel Corporation visited Scotland's Forth Road Bridge last week to work out how £12M of dehumidication equipment could be installed to curb main suspension cable corrosion. Cables were opened up in 2005 (NCE 6 January 2005) and found to be rusting, with some wires having snapped altogether. This has reduced the load-carrying capacity of the bridge.
Bridge operator Forth Estuary Transport Authority has commissioned consultant Faber Maunsell and Nippon Steel to produce a dehumidication system that involves wrapping the cables in a neoprene sheath and pumping dry air through to remove moisture, and stop further rusting.
Engineers were examining the saddle detail, where the cables sit on the main towers, to check that a hermetic neoprene seal could be achieved. Nippon has installed similar equipment on 10 bridges in Japan, but this will be the first time it has been retrotted to a structure that is already rusting.
Installation will take place in 2007, but it will be around 2010 before it is known whether the solution has been effective.