By David Reed, UT EditorKrefeld, Germany-By Monday 15 August-and barely five weeks after work started-the 70-m long by 11.5-m wide bridge on the A56 Autobahn south of this Rhine valley industrial centre should be fully back in use, and with a higher load-carrying capacity.Both the speed of refurbishment of the bridge-which saw the replacement of a total area of 805 m2 of steel deck-and the higher load capacity, are down to the use of the revolutionary SPS (sandwich plate system) technology developed in the last five years by polyurethane specialists Elastogran GmbH and a Canadian engineering concern, Intelligent Engineering. But a key role was played by the local branch of the giant Krupp Stahlbau Hannover concern, based in Duisburg, which helped arrange all the local, regional and national permits needed to allow the new, unproven technology to be used in such a critical role. One German specialist present at the 3 Aug site visit by bridge builders, local authority representatives and some press reporters suggested that gaining this approval in such a short time was, in some ways, more impressive than the performance of the SPS technology itself.SPS comprises two steel plates, about 5mm thick, between which a stiff polyurethane elastomer is injected as a liquid which cures to yield the final composite, and the Krefeld bridge is its first such application in Germany. It is also one of the first applications outside of the marine sector where the SPS technology first, as it were, surfaced. Although unproven in this application, SPS has been used in more than 44 000 m2 of marine applications, in such areas as refurbishing load decks in RoRo (roll-on, roll-off) ferries. These projects used the same overlay technique which minimises the amount of preparation work as it avoids having to dismantle the complete deck which, at the very least, requires relocation of all the below-deck service pipelines and electrical wiring. The overlay process simply requires cleaning the steel deck surfaces, welding spacer sections to this surface, and then creating a cavity by welding a new steel plate over the spacers. This cavity, typically 20-30 mm thick, is then filled by injecting the liquid PU system which subsequently cures and bonds to the steel surfaces, creating the tough sandwich. The injection process takes a matter of minutes, with full cure occurring within half an hour. The refurbished elements can be back in use within hours, a key benefit in areas where time out of uses is highly critical, as is the case with bridges as well as the ships repaired using SPS.Such construction have been subjected to a massive programme of testing both in the laboratories of Elastogran and its BASF parent company, and in large-scale simulations, principally at the RWTH (Rheinisch-Westfälische Technische Hochschule), the Aachen, Germany-based technical university, specialising in science and engineering education and research.The behaviour of the resultant composite meets or surpasses all the operational requirements and significantly extends the fatigue life of the bridge, the RWTH specialists reported.The next issue of Urethanes Technology magazine, October/November 2005, will contain more details of this project and the SPS process.“
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