Replacement of the Flaach-Rüdlingen Rhine bridge

A bridge has connected the two banks of the Rhine at the same spot for almost 150 years. It is embedded in a magnificent and unspoilt floodplain landscape. In 2014, various weak points were identified in the existing bridge structure. As a result, the use of the old bridge had to be restricted. From then on, it was only possible to drive on it in one-way operation with traffic lights.

Project description

The old bridge was moved towards the headwaters over a weekend using temporary structures previously erected in the river (transverse displacement, full closure to traffic). There it could continue to be used as an auxiliary bridge for all traffic for around one and a half years without any additional restrictions. The new bridge was erected in the shadow of the auxiliary bridge, in its original position, on either lifted or inserted Corten steel girders, which serve as the main supporting structure in conjunction with the carriageway slab. Following the construction of the bridge surface, the service lines in the foreshore area and in the bridge soffit, the solid railings with a duplex finish and the adaptation work on the road structure on both sides of the river bank, the new bridge was opened to traffic on 16 October 2023. The crowning glory was the extensive dismantling of the temporary bridge with the associated massive substructures. The new horizontal alignment is based on the old road, which could not be changed due to military history and nature conservation reasons. The bridge axis remains unchanged. The narrow carriageway width of 6.50 m (in a straight line) reflects the construction standard of the connections on both sides. For slow-moving traffic, there is a footpath on the downstream side and a cycle/walking path on the upstream side. The pier crowns on the existing shell limestone structure were replaced with new reinforced concrete load distribution slabs. The abutments were completely replaced on both sides of the river, with the fixed point on the south side (ZH) and the movable side on the north side (SH). A lightweight steel-concrete composite girder forms the new superstructure. Two low-maintenance, airtight welded box girders made of Corten steel were supplemented with a reinforced concrete carriageway slab, which serves as a falsework. 

Hydraulic engineering Preparatory work for cross-pushing  

For the planned transverse movement, 34 piles with a diameter of 900mm had to be drilled into the river bed (molasse), 24 of them from the pontoon. The pontoon used was around 30 metres long and 12 metres wide and had a payload of over 130 tonnes. The "barge" was mainly steered using cable winches installed on the pontoon. The steel cables were attached to three anchors on land. The main difficulty was to achieve the required accuracy when moving the steel supports on unstable ground.

Concrete work on bridge slab  

The Doka ParaTop bridge formwork system was used for the formwork work on the bridge deck. This is a system that can basically be operated from above and is anchored to the substructure using installation shoes. Challenges: 
•    Realisation of the extremely demanding requirements of the client and site management for the formwork pattern (e.g. continuous formwork panel joints across the three cross-sectional areas) 
•    Compliance with the geometric specifications and lines (widening of the floor plan in the south, arch in the longitudinal section, variable cross slope, 2x cove in the interior element) 
•    Handling the inner element when stripping above the water 
•    Monolithic construction in the fixed bearing area on the south side
 

Dismantling of the auxiliary bridge incl. substructure  

Once the carriageway slab had been removed, the remaining steel structure was lifted out bay by bay. The solid substructures could then be dismantled.