New construction to replace the Rothof Valley bridge

A solid construction using pre-stressed concrete

Ralph Pellegrini

The new valley bridge in the north of Bavaria. (Image: PORR AG)

Close to the Lower Franconian towns of Rottendorf and Rothof in northern Bavaria, PORR is working to construct a replacement for the Rothof Valley bridge. The existing structure no longer meets the requirements of modern traffic loads, and is to be replaced by a new bridge in a six-lane expansion of federal autobahn BAB A7. The contract has a total net value of around EUR 31 million.

The Rothof Valley bridge was built in 1965 as a single-piece steel composite cross-section, spanning the Würzburg-Bamberg rail line. Considerable damage can now be seen on load-bearing sections of the existing structure; structural examinations of the bridge have ascertained that it is no longer possible to retain and repair the existing structure. In January 2017, following a public call for tenders issued by the Federal Republic of Germany, represented by the Autobahn Directorate for Northern Bavaria (Autobahndirektion Nordbayern), PORR Deutschland GmbH . Berlin branch was awarded the contract to construct the replacement for the Rothof Valley bridge. The planned replacement bridge also aims to enhance water conservation markedly, with construction of a new site draining facility and a settling basin below the bridge construction site as a rainwater retention basin. Construction work started in April 2017, with completion planned for May 2021.

The project

The new bridge is designed to accommodate a possible six-lane expansion of the A7. However, the current number of lanes – and, therefore, the transport function and capacity - will not change. To facilitate the traffic flow during the construction period, it is necessary to relocate the traffic lane towards Fulda to a temporary replacement position beside the existing structure, with a carriageway width of 14.50m. The superstructure for the lanes towards Fulda is supplied prefabricated and placed on temporary auxiliary piers. After the lanes towards Würzburg have been completed and all traffic on the autobahn has been diverted on the superstructure of the lanes towards Würzburg, the superstructure created in the replacement position will be inserted transversely. The temporary auxiliary piers will then be removed following transverse insertion of the superstructure. The existing bridge structure will be demolished in stages as the transversely and longitudinally pre-stressed carriageway is dismantled. The steel structure is supported by auxiliary supports during this process to assist while loads are redistributed.

Technical details of the construction

The new Rothof Valley bridge is to be completed in solid construction using pre-stressed concrete. Lanes in both directions of travel will be given a superstructure with a box-type cross-section. The superstructures are constructed in the incremental launch method with 15 girder sections, each approximately 30m in length and 3.70m tall. A stiffened steel nose section with a length of 36m is used in this method. The superstructures each have a total length of 410m, and are spread across two abutment axes and seven pier axes. The largest distance spanned is 60m. The superstructures are moved using spherical bearings on solid piers which, in plan view, form a knee-like shape. The solid piers run diagonally upwards on all four sides and finish with a Y-shape at the top. The superstructure for lanes towards Fulda is launched over the previously installed temporary piers in the incremental launch method. Following completion, including railings and surfacing, all traffic on the BAB A7 will be rerouted over this temporary superstructure.

View into the incremental launch site (Image: PORR AG)
Reinforcement in prefabricated sections (Image: PORR AG)

After the existing bridge structure has been demolished, final substructures will be created for lanes in both directions. The second substructure for the lanes towards Würzburg will then be created and moved to their final position in the incremental launch procedure.

After the lanes towards Würzburg have been completed, the BAB A7 traffic will be redirected once again. As a result, the superstructure for lanes towards Fulda, currently in the replacement position, can be transversely inserted into its final position. The transverse stroke bearings are based on special plain bearings for all bearing axles. The necessary displacement forces are introduced via the pier axes.

Project data

Client Autobahndirektion Nordbayern
Contractor PORR Deutschland GmbH . Infrastructure . Civil Engineering, Berlin branch
Project type Infrastructure . Bridge construction . Structual engineering
Project scope Construction to replace the Rothof Valley bridge
Construction start April 2017
Construction end May 2021
Country Germany

Technical data

Project length 410m
Superstructure height 3.70m
Height from ground 32m
Internal pre-stressing steel approx. 450t
External pre-stressing steel approx. 165t
Rebar steel approx. 4,175t
Concrete bored piles approx. 7,200m³
Concrete substructures approx. 10,400m³
Concrete superstructures approx. 13,305m³
Pier heights 12.50m to 22.50m

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