Building over, under and through: Bypasses for the Voest Bridge in Linz

The Voest Bridge has been in use as part of the A7 Mühlkreis Autobahn for more than 40 years, with around 100,000 motorists using it to cross over the Danube each day. However, the time has come to renovate this heavily used road. To keep traffic flowing during the refurbishment and to increase capacity, bypass bridges are being added to the cable-stayed bridge over the Danube. Once the additional bridges have been constructed, highway traffic will cross over on the existing bridge, and traffic to and from the city centre will be directed over the two new bridges.


Solid foundations on land and in water
Building four oval piers in the middle of the surging Danube poses a technical and logistical challenge. Sheet pile boxes are used to create dry space for the concreting of the base on which the piers will be built in two sections. These massive columns are around 15 m tall, 4.5 m wide and up to 19.7 m long. The formwork comprises wooden boxes made of Top 50 elements, assembled by the Doka pre-assembly service. Exceptionally strong special connection lugs are installed to transfer longitudinal anchor loads, which eliminates the need for tie rods on the longitudinal side and through the curves. The piers are concreted using two different types of concrete to provide an outer area that is particularly resistant to the wear caused by the strong flow of the Danube. Of course, constructing the oval foreshore piers on land is a little easier. Special lugs are also used for the formwork here. The river piers and the oval foreshore piers all have a fine, regularly structured surface as the pier formwork features matrices and trapezoidal bars.

Round piers support the numerous entry and exit ramps. Around 20 of these piers, which measure 1.20 m in diameter, are made from RS steel column formwork in a special design. Pre-assembled wooden box formwork made of Top 50 large-area formwork is used for seven piers with a thickness of 2.0 m.


Structures for advanced lane management
On the Linz waterfront, in construction section LZ33, the existing superstructure on both carriageways is being widened by up to 9.5 m over a distance of 350 m. The shoring is provided by a fast and efficient combination of Dokamatic tables with the Staxo 100 load-bearing tower. Where the deck meets the widened support structure, the consortium is building a 165-metre-long retaining wall including a cantilever slab. The Top 50 formwork elements are largely anchored in place without ground support.

Traffic into the city will be separated from through traffic at the Urfahr junction, so various entry slip roads and exits have to be created. A large number of Staxo 100 load-bearing towers are to be used for the superstructure in construction section LZ35D. WS10 multi-purpose waling will be mounted to this structure and fitted with H20 top formwork beams and the 3-SO formwork sheet. The concrete for the ramp structure, measuring around 100 m long, is then poured in one step. The subsequent curved passage LZ35C, measuring around 250 m in length, will be made up of eight sections, with the base slab constructed in advance. The bottom formwork for the box girder cross-sections here sits on a Xervon falsework. Alu Framax Xlife framed formwork is used as the internal formwork for the sidewalls. Top 50 large-area formwork on Staxo 100 load-bearing tower is used for the outside of the sidewalls and the cantilevers. Doka demonstrates an impressive level of technical sophistication: the site team works using special shifting trolleys on castors to enable fast and efficient manipulation of the Staxo units. The sidewalls and deck slab of the superstructure for sections LZ35A and LZ36A are also concreted in one pour along their length of approximately 100 m. The steel superstructures over the Danube will link directly to these sections once they are completed. In the coming months, construction sections LZ35B, LZ36B and LZ36C will be constructed as slab superstructures.

A successful combination of steel and concrete, the bypass bridges are expected to be completed by mid-2020. Doka is impressing everyone on the Voest Bridge construction site with its ability to supply large quantities of materials for the superstructure formwork and with the technically sophisticated details of its work.


See for yourself:
Anyone interested in learning more can follow the progress of the construction of the A7 bridges on Facebook, where photographer Mike Wolf is documenting the work in detail. The ASFINAG webcam also displays new images of the bridge construction every day.