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Inflating an 80-Ton Concrete Shell

Concrete shells are efficient structures, but have not been considered resource-efficient due to the amount of material and labor involved.

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Concrete shells are efficient structures, but not considered resource-efficient. The formwork for the construction of concrete domes alone requires a high amount of labor and material. A new, more efficient alternative construction method called Pneumatic Forming of Hardened Concrete (PFHC) has been invented at TU Wien by Dr. Benjamin Kromoser and Prof. Johann Kollegger at the Institute of Structural Engineering.

A simple air cushion and additional post-tensioning tendons transform a flat concrete plate into a double curved shell. Thus, the complicated spatially curved formwork and the framework are redundant. The Austrian Federal Railways Infrastructure is currently building the first test construction on a scale of 1:2 in Carinthia, in the south of Austria.

The construction method consists of casting a flat concrete plate with wedge-shaped outlets. After the concrete is hardened, the air cushion placed underneath the plate is inflated and the post-tensioning tendons at the circumference are tensioned until the final form is reached. Glass fiber-reinforced plastic rods are used to absorb the occurring strains in the concrete plate.

If the flat plate is produced accurately, the construction method can save up to 50 percent of the concrete as well as 65 percent of the necessary reinforcement steel.

The test dome, built on behalf of the ÖBB Infrastruktur, has a length of 26.5 meters, a width of 19.1 meters and a height of 4.2 meters. It will be used to improve the construction technique for a first large application on a deer pass over the twin-track railway line "Koralmbahn" in 2017. Recently, the transformation process of the test dome was successfully finished, weighing 80 tons and lifted with only 20-22 millibar from the flat plate to the spatially curved shell.

The next steps will entail adding an additional concrete layer and cutting away some excess material. The final building will be available for events this summer.

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