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It is common knowledge that building a bridge over a motorway is no easy matter, insofar as it inevitably entails lengthy closures and considerable disruption to the regular flow of traffic. Now the technology of composite bridge elements is changing all that.
(Published on January-February 2006 – JEC Magazine #22)
Traditionally, civil-engineers have had recourse to the ‘composite’ properties of concrete and steel when designing bridge structures. The advent of advanced composites, however, seems to be pointing the way forward towards a whole new generation of structural elements in bridges.
The challenge facing ACG, specialized in supplying advanced composite pre- preg materials to sectors as varied as motorsport, aerosport, building and marine applications, and NECSO Entrecanales Cubiertas, the Spanish construction specialist, was to design and build a road bridge over the busy Cantabrico motorway in Spain, a n d this through the transfer of technology from ACG to NECSO.
The partnership to work at first on an experimental beam associated ACG and the European Commission for Joint Research in Italy at the ELSA laboratories. The latter brought together NECSO and ACG as the material supplier and techno- Spanning the future 52 JEC Composites Magazine / no22 January-February 2006 Successful partners USE RS’ PLATFORM It is common knowledge that building a bridge over a motorway is no easy matter, insofar as it inevitably entails lengthy closures and considerable disruption to the regular flow of traffic. Now the technology of composite bridge elements is changing all that.
logy developer respectively. The government of the Asturias was also involved; two Spanish Ministries (Infrastructures & Public Works and Science & Technology) are the end-users, and so this was a fully commissioned project and not a simple research one. The University of Saragossa also contributed by supplying materials evaluation, tests and modelling.
“NECSO selected AGC’s prepreg technology to ensure that actual laminate properties were as close to design predictions as possible and that necessary quality control was maintained from material spcification through to component manufacture.
We both drew on a great deal of project research background, already done by ACG in joint activities with their partners’ laboratories. The bridge project was developed over an intensive 6-month period. Alongside manufacturing and development, much material and process optimization work was carried out between us as well.
We continue to be involved in ground- breaking civil engineering projects with advanced composites and I know that NECSO will gradually extend its know-how all over Spain and further afield.”
An obvious choice
From the outset, it was an accepted fact that the use of composites – in this case a high-strength, uni-directional, bi-axial carbon fibre, pre- impregnated with a special epoxy resin and with a polymer matrix – would provide the bridge elements with all the necessary structural strength.
The composites would offer a very high stiffness and strength to mass ratio, higher than found in both concrete and steel. The finished elements would offer excellent environmental properties and corrosion resistance; lightweight, they could be produced in modular sections, offer ease of handling and be assembled rapidly on site. The ultimate benefit to the user would be massive time-savings and hence great reductions in costs associated with road-closure, labour, and site-handling equipment.
The first stage of the programme lasted 6 months and produced the trial beam (5.5m) ; under load testing at the Torja Institute in Madrid, it was observed that the beam sustained a failure load of 17,000kgs, where the design load had been set at 9,000. Another vital aspect was that the beam weighed only 15% of the total weight of a conventional beam in reinforced concrete.
The next stage was a longer beam, manufactured and tested to design limit at the ELSA laboratories. The partners then moved on to the final stage of full-scale beams (3 sets of 4) to span the bridge, 46m in length and 8.1m in width, with much material and process optimization work carried out between ACG and NECSO.
One of the main advantages of building the bridge in this way was that the time the road underneath needed to be closed was greatly cut, so overall expense in terms of crane, haulage and labour costs were also considerably reduced. Indeed, the bridge went up in only 3 days, in March 2004, compared with the 40 required for an equivalent, conventional structure. Entire units could be delivered to site, where they were jointed together and hoisted on to the pre-cast concrete support columns in one single operation. The concrete deck road surface was cast in situ and the beam elements were anchored to the abutment.
Such ground-breaking technology could hardly pass unnoticed and recognition came at JEC Composites Show last year when ACG and NECSO ran out winners of a prestigious JEC Award in the “Construction” category. Technical performance and commercial competitiveness were two of the arguments which swung the judges in their favour.
The bridge is now in use, complete with a whole set of self-monitoring systems, such a fibre optic centres; it is also under continuous observation for the gathering of data, for instance into the questions of fatigue and effects on the environment. During the bridge’s first ten months of service, no reduction in performance has been observed. It may just be a matter of time before all bridges will be built, using this technology and these materials.