2005-11-12

Old Forth Road Bridge Needing Repairs ASAP

'The Forth Road Bridge' will be closed to all traffic in 14 years' time unless its corroded main cables are fixed... Cars will be barred from the crossing in 2019 -- even if a threatened lorry ban is introduced in 2013 -- according to the latest assessment of the corrosion. 'The Scottish Executive', which confirmed the information, added that it was 'highly likely' the 41-year-old bridge would have to close if the cables had to be replaced. It is understood the bridge authorities may try to prevent the corrosion getting worse instead by blowing dry air through the 600_mm-thick cables, which could cost 12_million_GBP. Some of the 11_618 pencil-thin wires making up each cable have broken, and experts said attempting repairs would be very complex and expensive. They added that complete replacement of a main cable was almost unheard of. The Transport Minister Mr.Tavish Scott, announced an independent assessment of the state of the bridge on Thursday after being told the latest inspections showed the corrosion was worse than was previously reported. A full report is due to be considered by 'The Forth Estuary Transport Alliance' ('FETA'), which runs the bridge, later this month (2005-11). 'The Scottish Executive' said yesterday (2005-11-11) the 'closure dates' were based on assessments of the state of the cable in the sections inspected so far, together with the weight of traffic on the bridge. These were then used to calculate how soon the corroded wires in the cables are expected to break. It is understood that 'FETA' may attempt to halt further corrosion with a dehumidification process, which is already used to keep the cable's wires dry in the bridge's anchor chambers. This is where the individual wires are exposed at the point at which they are fixed to the ground. The process would involve huge cylinders from which dry air would be pumped into the cables at various points. Mr.Michael Albergo, the vice-president of 'Weidlinger Associates', US American-based specialist bridge engineers, said repairs to broken wires within a main cable would not be easy. He said severed wires could be spliced, but if they were towards the centre of the cable it would have to be wedged open and repairs completed without damaging the other wires. Mr.Albergo said if the main cables needed replacement it could give the opportunity to increase the traffic capacity of a bridge, such as by widening the deck or adding an extra deck. This is being considered for two of the first bridges in the world in line for new main cables -- 'The Bronx-Whitestone Bridge' in New York City and 'The Benjamin Franklin Bridge' in Philadelphia. However, another international bridge expert, who asked not to be named, said all suspension bridges suffered from corrosion and the problem should not be exaggerated. He said:
'Money must be spent on all such major bridges to slow down their corrosion, but there is no reason to build another bridge for this reason alone.'
However, he said heavy traffic could cause other damage to a bridge, such as metal fatigue to its deck, but this could often also be addressed with maintenance. 'The Forth Road Bridge' is carrying 24 million vehicles/year, which is twice its design capacity. Heavy lorries have been blamed for the need for increasingly frequent repairs, such as resurfacing of the carriageways. 'Forth bridge closed to cars by 2019', Alastair Dalton, The Scotsman, 2005-11-12' Links: Forth Bridges Visitor Centre Trust Forth Estuary Transport Alliance ForthRight Alliance

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