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Making bridges saferAn engineering research project at Monash University is helping to accurately determine the strength of old bridges - and when they are in danger of collapsing. SUE McALISTER reports. Bridge failure can be highly dangerous, inconvenient and economically damaging, specially where major roads are affected - so it is quite a scary thought that thousands of bridges throughout Australia have 'use-by' dates that may already have expired. A team of Monash University researchers, headed by Dr Riadh Al-Mahaidi and Dr Geoff Taplin, are finding ways of testing and accurately rating the integrity of old bridges without having to stress them until they fracture or fall down. The team, consisting of six academics and eight PhD candidates from the university's Department of Civil Engineering, is searching for solutions to this dilemma in collaboration with Victorian state road authority VicRoads. "The project, which started in 1997, is expected to run for 10 more years because of the need for long-term monitoring of bridge safety and conformity with our findings and recommendations," Dr Al-Mahaidi says. "Our research is limited to bridges in Victoria, but our findings are applicable nation-wide." Over the past five years, VicRoads has contributed nearly $300,000 to the project. This year, the team also obtained a federal government infrastructure grant of almost $1 million, a major part of which will be used to acquire advanced testing and monitoring equipment for the bridge safety project. Several factors may compromise bridge safety. Until 1948, there were no clear codes of practice governing bridge design in Australia, and some bridges built prior to that date do not meet current design standards. Many of these structures are now deteriorating, especially in the coastal fringe where corrosion of reinforced concrete is increasingly common. As well, the 1200 reinforced concrete bridges built before that date were not constructed to support the increased number and weight of vehicles - which produce a magnitude of wear and tear unimaginable over half a century ago - that the bridges carry today. This means that bridges built prior to 1948 often 'break the law' - their official load rating (the maximum weight they are permitted to carry) falling far short of what is currently required of them. Dr Al-Mahaidi says he is very encouraged by the results so far - and excited too, because the research is not just applicable to bridges. "Over the last two centuries, we have put up all kinds of buildings in Australia, and now there is concern about their safety - can they really keep up with modern loads and environmental effects?" The project is both theoretical and experimental. Using methodologies identified by the Monash team, VicRoads conducts the testing of bridges in the field, then gives the resulting information to the team, which uses it to evaluate and further develop its theoretical models for assessing bridge strength. To aid their work, the researchers have some heavy-duty equipment at their disposal which includes load-testing machines, fire-testing facilities, concrete mixing and testing facilities, a constant temperature room and environmental chambers. There are also electronic data acquisition systems and advanced numerical simulation facilities. The Monash/VicRoads project started with an investigation into the shear strength (the weight a structure can tolerate before it deforms or fractures) of old reinforced concrete 'T-beam' bridges. The shear strength of many of these bridges was assessed as deficient when measured by current standards. The Monash team recommended using modified compression field theory to produce a more accurate assessment of strength than the current standard, and testing validated this approach. The project has also produced some surprising results. A 1916 bridge designed by Sir John Monash (after whom the university is named) and which had been closed since the 1950s because of fears it was not up to coping with increased traffic levels was found by the team to be at least twice as strong as previously thought. Nor was this, the Kiewa Valley Highway Bridge in northern Victoria, an isolated case. According to Dr Al-Mahaidi, some of the bridges earmarked for strengthening work by VicRoads did not require it at all. The validity of theoretical assessments of other components of bridge safety, such as a bridge's vital capacity to flex under unevenly distributed and/or mobile loads, has also been tested experimentally. And while many bridges have proven stronger than expected, others have given cause for concern, so the Monash team is also investigating the best methods of strengthening them, in particular, by exploring recent advances in materials technology. These have made it possible to 'retrofit' bridges, replacing old or worn parts with new and up-to-date ones using externally bonded fibre reinforced plastic composites - a new, competitively priced technique that the team considers superior to traditional ones. The Monash team is now collaborating with the University of Colorado in the US on assessing the safety of bridges and how best to strengthen those deemed unsafe using advanced carbon fibre composites. The team is also working with the University of North Carolina on how to use the composites to strengthen concrete bridges.
Safe as bridges: Civil engineering researchers (from left) Mr Huy Pham Binh, Mr Kuan Lee, Dr Riadh Al-Mahaidi, Dr Geoff Taplin and Mr Alan Hon are testing the structural integrity of bridges built prior to 1948 in Victoria, which were not built to support the weight they carry today. Photo: Peter Anikijenko Action box |
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