The bridge will be particularly appropriate in motorway widening schemes, because it can be prefabricated on site and the whole span lifted into place by one crane in a single operation, reducing disruption.
This development shows how the technological revolution in materials and processes elsewhere in manufacturing is finally beginning to catch on in construction, says Peter Head, technical director of the civil engineers G Maunsell and Partners, one of the companies working on the bridge project.
Mr Head believes the technology exists to build motorways that can be maintained, except for resurfacing, without disrupting traffic flow. The problem is that such structures require a higher capital investment. The new bridge will cost between 10 and 20 per cent more to build, but maintenance costs over the life of the installation will be up to 30 per cent lower at today's prices.
Instead of single girders, the bridge has a geometric network of steel supporting the concrete deck slab. This allows the thickness of the concrete slab to be reduced from about 250mm to 150mm. As a result, there is a 40 per cent weight saving - a 20m-span, two-lane bridge, including the concrete deck, will weigh less than 100 tons, well within the capacity of mobile cranes.
The whole structure is encased in plastic reinforced with glass fibre. This protects the steelwork from the atmosphere. It also allows access from the deck level to the steel structure for maintenance, avoiding the need for scaffolding that would restrict traffic beneath. The enclosure also contributes to the strength of the bridge.
A 12m span of an almost full-scale section of bridge, with steelwork donated by British Steel, has been successfully tested by Cambridge University engineering department over the summer.
Mr Head expects the first bridge using the new approach will be built in the next year or two. The companies involved in the design project are setting up a company this month to develop and market the design.
He says the system can also be used to build long-span bridges, since sections of up to 150m can be manufactured in one piece. And the structure is light enough to be exported in prefabricated sections.
This is just one of the ways in which new processes and materials promise to transform the industry in the wake of the Cold War. Mr Head says companies that have lost business in defence and aerospace are looking for opportunities in construction, an industry with a huge turnover and little history of investment in R&D.
Proposed advances include improved concrete, stronger steel, aluminium and advanced composite materials, and new construction methods, including the use of robots. Like aircraft and cars, structures will come with a service manual and maintenance schedule.
The Department of Transport now requires disruption costs to be factored into quotes for road-building schemes. However, low-maintenance structures are not favoured by the Treasury, because they are more expensive to build.
Mr Head says privately funded road schemes will unlock innovation, because companies will have an incentive to avoid disruption that would reduce road toll revenues. 'Those controlling the design will also be responsible for long-term maintenance.'
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