The aluminum bridge over the A5 near Offenburg between Kippenheimweiler and Nonnenweiler.
In the Ortenau district of Baden-Württemberg, a maintenance-free aluminum structure has been running over the A5 autobahn since June 2015. The bike and sidewalk bridge can be easily dismantled and reassembled as needed.
The aluminum bridge completes the network of bike paths between Lahr and Schwanau. The structure has a span of 48 meters and a clear width of three meters. At the beginning, steel substructures were used for the structure. A retaining structure erected. For the superstructure, district officials agreed on an aluminum model from Peter Maier Leichtbau (PML) GmbH of Singen, Germany, designed as a free-floating truss trough bridge. The bridge also has a pavement elevation. A longitudinal superelevation is obtained. In winter, it can be used by snowploughs with a total weight of up to 7.5 tons.
What was wanted was a maintenance-free bridge
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It was also important to the clients that the bridge remains as maintenance-free as possible. Therefore all structural bridge parts were anodized. Jörg Petrowski, sales manager for bridge construction at PML, explains: "In this process, the metal surface is converted into a dense and very hard oxide layer under the influence of direct current in an electrolyte bath, which is firmly bonded to the base material."This protects the bridge from mechanical influences and also makes it resistant to weathering and corrosion. This is also why all the profiles were sawed, drilled and reworked before they were anodized. Only then they were installed. Another advantage of this approach, according to Petrowski, is the reduced clean-up effort: aluminum surfaces treated in this way can be cleaned without the need for costly graffiti protection.
Simple relocation of the free-floating upper bridge section
The transport of the bridge.
In order to avoid weak points in the construction – inclusions, pore formation or binding defects – the majority of welds were dispensed with. The expert also explains that the EN AW-6082 T6 alloy used has a maximum yield strength of 310 N/mm². The only welds are on the storage plates and platforms. All other load-bearing parts are bolted.
The bridge was completely built only about 500 meters from the intended location – by a construction company. The low loader was then used to transport the 4.40 meter high structure to the construction site. It was lifted with two truck-mounted cranes. Since there is no central pillar, the bridge can also be easily dismantled and rebuilt. This could become necessary, for example, if the A5 were to be widened to six lanes. The free-floating bridge superstructure could then be completely relocated to another site, just as it was when it was installed.