Wildlife Crossing AM2 in Carinthia, Austria
|Investor and Design||
Austrian Federal Railways (ÖBB)
|Geometry Optimization and Structural Analysis||
Technische Universität Wien
Institute of Structural Engineering
The wildlife crossing AM2 has been built with a construction method for concrete shell structures called Pneumatic Forming of Hardened Concrete (PFHC). This new method has been developed by the TU Wien in the context of the research project "Double Curved Shell Structures".
The new bridge spans the new double-track line of the Koralm Railway in the south of Carinthia. In order to test as many design details as possible, a first test shell on a scale of 1:2 was built, now being used as a roofing for events.
Functioning of Construction Method PFHC
First, a flat concrete slab with wedge-shaped outlets, in which wedge-shaped air cushions are mounted, is casted. On the slab's edge, unbonded tendons are placed in sheathes. Subsequent to the concrete's hardening, an air cushion lying underneath is blown up, transforming the concrete slab into a double curved shell. At the end of the transformation, the tensioning cables are prestressed additionally. They are anchored as soon as all joints are sealed with concrete or grout.
Construction of Wildlife Crossing
The thickness of the transformed shell is 10 cm and supplemented by a concrete topping of 35 cm. Fine cracks arising during the transformation are sealed by this additional layer of concrete. The bottom side of the shell is free from cracks due to the compression zone located there during the transformation.
The entire shell structure of the bridge has ground plan dimensions of 36.7 x 38.7 m and a height of 8.9 m. Its shape is based on the supporting structure's optimization corresponding to the occurring loads and given boundary conditions. Due to this optimization, a state of membrane stress is reached which is favorable for the structural behavior.
The ecological balance of the wildlife crossing has been impressive. In comparison to a reinforced concrete frame originally planned as a crossing alternative, the environmental pollution could be reduced by about 40%, evaluated with regard to the global warming potential (CO2 equivalents).
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