More than 30 years of planning and approval procedures, 13 bridges with a total length of 2.3 kilometers and 880,000 cubic meters of earth movements: The extension of the BAB 46 motorway between Velmede and Nuttlar is one of the most unusual road construction projects in North Rhine-Westphalia and is scheduled for completion in 2017. The Nuttlar viaduct is a construction highlight and at the same time the greatest challenge. Its height of 115 metres above the valley floor exceeds the previous record holder, the Siegtal Bridge near Siegen, by five metres. Max Bögl's bridge construction experts were responsible for the construction of the 660-metre long, curved Talbrücke, which rests on six striking pairs of A-shaped double piers.
Over the abyss in eight cycles
Due to the great height above the valley, spans between 77 and 115 metres and the very narrow routing in this motorway section, the client, Landesbetrieb Straßenbau NRW, dispensed with the usual separation of the superstructures and substructures in each direction of travel. Instead, a superstructure covering the entire width of the motorway was constructed as a one-piece steel composite box girder with an external strut construction. For this purpose, almost 150 steel components were manufactured in the company's own steel structure in Sengenthal, assembled on site in the cycle cellar behind the eastern abutment and pushed west over the piers in eight individual cycles. For the longitudinal displacement of the bridge segments with the aid of a 30-metre-long front beak, a cable pull system with strand lifters was used.
Distinctive double pier design
As light as the steel superstructure seems to float over the valley between Sengenberg and Suhrenberg, so filigree are the double pillars that support it at lofty heights, thin as asparagus peaks protruding from the ground. The massive concrete round piers, stiffened by horizontal steel round beams, rest on massive foundations the size of a single-family house. Four identical composite formwork carriages travelling at the bottom produced the 28.60 metre wide carriageway slab with a constant transverse gradient of four per cent using the pilgrim step method. First, the cycles were set in the middle of the field, followed by the closing cycles above the piers. At peak times, around 100 skilled workers were employed on the construction site. When the Nuttlar viaduct, the construction of which was completed in 2016, can finally be opened to traffic, is still open. For the extension of the A 46 between Velmede and Nuttlar, no concrete end of construction is in sight.
