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Faster. . . lighter. . . stronger

Bridges - Senior Highways Agency and Network Rail engineers say that new materials are starting to revolutionise road and rail bridge construction. John McKenna spoke to them.

More and more bridges across the UK will start to incorporate carbon fibre reinforced polymer, rather than steel and concrete.

This is the prediction of senior engineers from Network Rail and the Highways Agency, who between them are responsible for maintaining 77,000 bridges.

The use of carbon fibre reinforced polymer (CFRP) plates and mats to strengthen bridge beams has become widespread since the Highways Agency approved them for highway structures in 1999.

CFRP wrapping for columns has also become an increasingly popular strengthening method since successful trials three years ago. The reinforced polymer was first used in the UK in 1992 on the 63m span Aberfeldy footbridge in Scotland.

The steady rise of carbon fibre composites in bridges since then has led to the Agency commissioning a footbridge across the M6 constructed entirely of fibre reinforced polymer. The bridge, at Mount Pleasant, Lancashire opened in June.

The trend towards CFRP is set to continue, according to Highways Agency head of research and development of standards Gerry Hayter.

'We have used fibre reinforced polymer decks on a couple of the bridges that we've put up over the M6 and we really see this is as an area that will grow, ' says Hayter.

'We've been encouraging development for a number of years and this material does offer a lot of advantages, particularly in speed of construction.' Hayter's views are shared by Network Rail head of major structures Andrew Clayton.

'We are already bonding carbon fibres onto existing bridges to strengthen them, ' says Clayton.

Hayter says the Agency wants to push ahead with the development of new materials and techniques to help the new wave of motorway widening projects now coming on stream.

'What we are looking at are techniques and innovation that really will cut the impact on drivers, because obviously on the motorway widening schemes we are dealing with constructing in a live traffic situation.' A bridge made from fibrereinforced polymers has a number of advantages.

The polymers are lighter than traditional construction materials, so bridges are easier and quicker to lift into place.

They can be placed complete with guardrails and surfacing, saving time and resources while minimising traffic disruption.

'The network is very busy and from a structures point of view.

We are constantly on the look out for materials and techniques that will enable the construction process to be carried out with minimum disruption, ' Hayter says.

'Given we've got the M25, M1 and M6 widenings, there should be ample opportunity for new techniques to be developed and applied widely.' The economic benefits of using carbon fibre technology can be seen in other ways too, says Hayter.

'With CFRP we believe it reduces whole life cost in terms of maintenance in the longer term, ' he says.

'We are looking at the decks we have put in [on the M6] and we will be looking at how these perform. It's early days but the indications are very promising that these new materials do have a lot to offer.

'The column wrapping has had a significant benefit in terms of reducing cost of upgrading columns for enhanced impact loading. It is something that has quite quickly become popular and many would now view as mainstream.' Clayton says Network Rail has alteady begun to see the benefits of using carbon fibre technology in bridges. And, like the Highways Agency, Network Rail wants to push the technology further.

'We are now looking at building a new bridge of entirely carbon fibre reinforced polymer, probably a footbridge, ' says Clayton.

Clayton sees the rising use of carbon fibre materials as an indication of Network Rail's insatiable appetite for prefabricated materials for maintenance and enhancement works. The refurbishment of the Leven Viaduct near Morecambe is an example (NCE 25 May).

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