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INFRASET SCORES DOUBLE HONOURS IN 2007 FULTON AWARDS | Click HERE to go back to awards The awards were made to INFRASET Railway Products for its Universal/Infrabolt concrete sleeper project – a world-first in rail sleeper technology - and to INFRASET Pipes, Culverts & Manholes for its participation in the building of an innovative footbridge over the Mkomaas River – Africa’s first pretressed concrete ribbon bridge. Consulting engineers, Jeffares & Green led the footbridge project which is situated near Richmond in KwaZulu-Natal. The bridge has a clear span of 150m which equals the world record for a ribbon bridge. Not only is the Universal/Infrabolt concrete sleeper a world-first in concrete sleeper technology, but the project is currently saving Spoornet R100-millions by being used to replace 15 000 ageing timber-based turnout sets countrywide. The breakthrough came in 2005 after Spoornet had spent several years searching for an alternative to scarce and expensive imported timber sleepers. Developed by INFRASET in close collaboration with Spoornet’s Track Technology Centre and Metrorail, the new sleeper system overcomes formidable technical obstacles and is installed simply and easily. The key to the system is an innovative rail-to-sleeper fastening system, Infrabolt, which enables concrete sleepers to be installed under existing track and for bolt holes to be drilled on site. INFRASET Railway Products director, Kobus Burger, says it is anticipated that the performance of the system will be comparable to the 30-year lifespan of a completely new state-of-the–art concrete sleeper turnout set. “However, it achieves this at a capital outlay of only 20% of a new set which costs in the order of R1 million. A more obvious advantage of Universal/Infrabolt is that it ensures a constant and reliable sleeper supply. Another major benefit is that the system is manufactured using local labour and materials, thereby creating jobs and stimulating the economy. It also makes ecological sense, conserving the world’s dwindling timber resources and obviating the need for the chemical treatment of wood, which is harmful to the environment,” observes Burger. Commenting on the project the Fulton Award judges said: “The design and construction methodology incorporating reinforcement markers and specially designed anchoring systems, enable concrete sleepers to be cut to length and drilled to any size or configuration depending on the design of the turnouts. Although concrete sleepers have been available for many years it has not been possible to use them for turnouts or more complex track configurations. The sleepers have overcome these constraints to the benefit of the client. Furthermore they offer the client a more economical and durable alternative to the wooden version. To further exhibit their versatility, these sleepers have been used in lengths of up to six metres. This unique South African design, which is gaining world interest, is truly a worthy winner of the Fulton Award’s Special Category .” The Mkomaas River Bridge consists of a ribbon of precast concrete elements suspended from cables which were tensioned between abutments. In making the award the Fulton Award judges noted that simplicity in design and execution made the bridge a popular winner. They observed that it required a solution which was aesthetically pleasing, robust and economical and one which would use unskilled labour. “The location of the project and nature of the river also mitigated against a traditional solution,” commented the judges. Manufactured by INFRASET Pipes, Culverts and Manholes, the concrete deck elements were joined and compressed over the full span of the bridge by tensioning a second set of cables which was threaded through ducts precast into the concrete elements. The resultant compressive strength not only provides continuity through the deck but also compensates for tensile stresses during live loading. Corrie Meintjes, a senior partner at Jeffares & Green, was the person responsible for finding a design which would soothe community concerns about the movement associated with several other popular bridge designs such as cable stayed, suspension and hybrid bridges, and one that would provide a single span over 150 metres. Meintjies said that the launching rate of INFRASET’s concrete deck elements exceeded the designers’ best expectations. “Twenty-four deck elements were launched in a single day, making the launching of the entire ninety-three elements a five-day operation. Adjustments to the cable forces had to be made so that the bridge deck elements could be leveled prior to throwing concrete in situ. “The adjustments were necessary owing to the combined effect of a narrow deck and small inequalities in large deflections of the catenary at mid-span, which were in the order of 4,3m. Once all the elements were in position, the downstream side of the deck, deflected about 50 mm more than the upstream side at mid-span. This meant that the tension in the cables on the downstream side had to be adjusted by about 0,5% of their ultimate tensile strength’” said Meintjies. Rolf Schutte, a concrete technologist with NPC-MPOR, says it is extremely exciting to see just how innovative structural engineers could be when faced with such challenges. “In this instance the concrete precast elements were manufactured off-site under factory conditions and then transported to this remote site. This ensured the high quality concrete product required for this high-tech structure. “The bridge does not interfere with the flow of the river in any way and there are no stabilisers, towers or large abutments to spoil the rural landscape. The extensive use of concrete elements ensures that the Mkomaas River Bridge will serve its community virtually maintenance free for many years,” concludes Schutte.
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