Four historic railway bridges renovated in the Bavarian Forest

Since around 1880, the Ohetalbrücke, Nagerlbrücke and Deffernikbrücke bridges have been part of the railway line between Plattling and Bayerisch-Eisenstein. The “Brücke über den Regen” bridge, built in 1938, is pretty young in comparison. To ensure that the aging bridge quartet is able to reach the end of its planned remaining useful life (2027), the Rädlinger civil engineering team renovated the structures for DB Netz AG in summer 2015 in close cooperation with the Rädlinger structural steelwork division.

In the three-month construction period, up to 100 people were working on the four steel bridges at the same time – sometimes around the clock and seven days per week. There was plenty to do during the complete closure of the railway line: in addition to corrosion protection works across an area of over 8,000m², the qualified employees carried out the replacement/new construction of steelwork components with a total weight of approx. 150t, the renovation of around 2,500m² of masonry joints and the installation of a 550m-long cable conduit, amongst other things.

Access to the bridges was not always possible during this period. In places, the workers thus set up construction access roads across the tracks and designed special transport carriages, which were able to travel along the walkways of the bridges even while the tracks were removed. The difficulty in accessing the site was evidenced once more during the renovation of the abutment and associated armature work. The relevant areas were not accessible with conventional drilling instruments. However, a walking excavator with its independently controllable legs was able to secure a stable hold for the drilling works.

The replacement of the approx. 15,000 rivets with HVP bolts required particular precision. These high-tensile bolts allow no deviation whatsoever when it comes to threaded boring. Since the replacement of so many rivets on such an old structure had never taken place before, a structural engineer remained on-site for long periods of time so that any questions arising around the stability of the structure could be immediately clarified. The existing steel of the bridges, built around 1880, also placed stringent demands on accuracy due to its composition. Thanks to its high carbon content, this steel does not rust, but it can also not be welded. Even the smallest of deviations can thus not be corrected at a later point.

Trains are now running over the 20km-long section again: over twelve new calotte sleeve bearings, six lateral bearings, 600 running metres of new track panels and even over a completely new track unit on the Nagerlbrücke. The Rädlinger team also renovated the upper structure on the exterior of the bridges over a length of approx. one kilometre. A total of approx. 1,700 m² of brand-new, glass fibre reinforced GFK grates on the side passages ensure safe access for further maintenance of the four bridges until the end of their extended lifetimes.

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