transportation
The pneumatic forming process starts with a flat sheet of concrete. Photo: © Benjamin Kromoser
An air cushion is inflated, turning the concrete sheet into a dome. Photo: © Benjamin Kromoser
Another layer of concrete strengthens the structure. Photo: © Benjamin Kromoser
A wildlife crossing over a railway is being built with a new construction technique replacing support structures with an air cushion. Inflatable bridge
bridge and the outside of the concrete structure will be backfilled with earth so that animals can use the bridge to cross the railway safely. Energy-saving, cost-effective, and resource-efficient The method offers some major advantages compared with traditional bridge building techniques. “The process requires a little more con- crete but 40 percent less steel,” Kromoser said. The TU Wien method is also more energy-efficient, reduces equivalent CO 2 emissions by 40 percent, and is significantly cheaper. “The costs are expected to fall even further once construction firms have gained more experience of using the new technique. We estimate that it could ultimately reduce costs by 15 to 30 percent,” Kromoser said. Since Kollegger first developed the idea of constructing a concrete structure using continuous forming rather than support structures, he and his team have worked hard to overcome each of the technical hurdles encountered on the road to developing a practical solution. It is rare for an academic development to be put into practice in a real-life construction project in such a short period of time. “We’re de- lighted that ÖBB had the courage to test out such an innovative idea,” Kollegger said. “If the method is to become more widespread in the future, it is essential to have a real-life prototype construction. We’re especially pleased that our calculations about the resource efficiency of the technique proved accurate. Sometimes, you work through these ideas in an academic context, but when you actually put them into practice you find there are still lots of details that need improving. That’s why it was so exciting for us to be involved with the project right through to completion,” Kromoser said. The wildlife crossing is located on the Carinthia section of the new Koralm railway, one of ÖBB-Infrastruktur AG’s major infrastructure projects in southern Austria. Following completion of construction and terrain modeling work, earthwork is now continuing before infrastruc- ture for the high-speed electrified railway can be installed. Watch a video of the pneumatic forming process at www.youtube.com/ watch?v=gwcIg9EJ2sM.
The shell construction methods that are usually used to build bridges and domes generally rely on expensive support structures. However, a team of engineers from the Technical University of Vienna (TU Wien) in Vienna, Austria, developed a new technique that is not only cheaper, but also makes more efficient use of resources. Instead of using a sup- port structure, an air cushion is inserted underneath the concrete and gradually inflated during the construction process. The first major tests were carried out three years ago at a TU Wien test site, but now the new method has been used in a real-life project for the very first time by the Austrian Federal Railways (ÖBB-Infrastruktur AG). With the help of TUWien, the Austrian railway network operator successfully used the technique to build a wildlife crossing over a new section of track on the Koralm railway. From panel to dome to bridge The basic idea is simple: If you make regular incisions in a piece of orange peel, you can spread it flat on a table. The “Pneumatic Form- ing of Hardened Concrete” technique developed by TU Wien applies precisely this principle but in reverse, starting with a flat sheet of con- crete with wedge-shaped incisions and transforming it into a curved dome. An enormous plastic air cushion is placed underneath the con- crete panel and then slowly inflated once the concrete has hardened. Hydraulic-tensioned steel cables ensure that the concrete retains the correct shape during this process. “It took around five hours to inflate the cushion and create an elongated concrete dome with an internal height of 7.60 meters,” said Benjamin Kromoser from the Institute of Structural Engineering at TUWien, who developed the technique as part of his dissertation with Prof. Johann Kollegger and worked closely with ÖBB on the project. Each end of the concrete dome was then removed and archways in- stalled to create a bridge. The new Koralm railway will run under the
Information provided by the Technical University of Vienna (www.tuwien.ac.at).
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csengineermag.com
february 2018
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