Wildlife Crossing AM2 in Carinthia, Austria
Wildlife crossing AM2 was built using a construction method for concrete shell structures called Pneumatic Forming of Hardened Concrete (PFHC). This new method was developed by TU Wien in the context of the research project titled "Double Curved Shell Structures".
|Investor and Design||
Austrian Federal Railways (ÖBB)
|Geometry Optimization and Structural Analysis||
Technische Universität Wien
Institute of Structural Engineering
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 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 cast. On the slab's edge, unbonded tendons are placed in sheaths. Subsequent to the concrete 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 additionally prestressed. They are anchored as soon as all the joints are sealed with concrete or grout.
Construction of Wildlife Crossing
The thickness of the transformed shell is 4 in and supplemented by a concrete topping of 14 in. 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 120.5 ft x 127 ft and a height of 29 ft. 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 with a reinforced concrete frame originally planned as a crossing alternative, the environmental pollution can be reduced by about 40%, evaluated with regard to the global warming potential (CO2 equivalents).
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