The Siegtal bridge carries the A45 interstate over the Siegtal valley and the Eiserfeld district of Siegen at a height of around 100 metres. The prestressed concrete structure with twelve spans, built in the 1960s using cantilever construction with scaffold girders, is one of Germany’s biggest road bridges,, spans between 63 and 105 metres, and a total length of 1,050 metres. In the course of the expansion of the A45 interstate, the bridge has to be replaced by a new structure with traffic maintained throughout.

The exposed location above the town, a large number of intersecting traffic routes, the Sieg river, a rail line, and an overhead power line all make this an extremely challenging planning task.

The deconstruction of the existing bridge and the replacement structure cannot be considered independently here. As part of an extensive study of variants, a wide variety of demolition and construction concepts were considered. For the new Siegtal bridge, various alignment positions and systems – including prestressed concrete and steel composite girder bridges with spans between 100 and 200 metres using the incremental launching or cantilever method – were investigated. The current favorite is a cable-stayed bridge with spans of up to 192 metres built using the incremental launching method. Alongside structural engineering aspects, economic, design, and sustainability aspects were intensively investigated.