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S-curve formed in back-step sequence

11.09.2013 | Press
Doka composite forming carriage meeting tough requirements for 4-lane road bridge over River Oder in Germany’s Harz Mountains, on B 243 Barbis Bypass.

Impressions

  • The distance-pieces on the roller-trestle bearing supports keep the composite forming carriage safely aligned in the horizontal.
  • The composite forming carriage is designed to cope with the higher loads resulting from the large and non-uniform distances between the roller-trestle bearing supports.
This 496 m long steel composite bridge is being built with a massive, 20.36 m wide and up to 58 cm thick deck slab that has a 6 % longitudinal gradient and a transverse gradient of as much as 5 %. The S-shaped roadway has curve radii of 400 and 600 m. These extreme specifications, and the fact that the roller-trestle bearing supports are spaced between 3.78 m and as much as 4.90 m apart, mean that the composite forming carriage fielded here has to deal with some unusual and widely varying load conditions.

Changes in radius and transverse gradient

The first 346 m of the bridge roadway, which is being cast in a back-step sequence, takes the form of a right-hand bend with a 400 m radius. After this comes a 123 m long spiral transition curve into an approx. 27 m long left-hand bend with a radius of 600 m and a corresponding change in the transverse gradient. This section of the structure crosses a designated fauna/flora habitat zone with the only bridge construction of its kind in Germany, consisting of two steel half-arch superstructures with a total length of 130 m.

Various different distance-pieces and shims are used on the roller-trestle bearing-supports to compensate for the varying transverse gradient of the structural steelwork and to keep the 25 m long composite forming carriage aligned in the horizontal. The 24 casting segments, each of max. 23 m in length, are being poured in a ‘back-step’ sequence. Because every single casting segment has a different radius and transverse gradient to the one before it, the carriage had to be designed to cope with many different load situations. To minimise the work needed for these repeated modifications to the composite forming carriage, its constructional design – consisting almost entirely of rentable system components – has only one type of curve segment per longitudinal beam. This enables every single modification to the composite forming carriage to be carried out quickly and easily.

Composite forming carriage pre-assembled and dismantled by Doka

Doka Formwork Instructor Sven Mazalla is assisting the site with project-related advice and consulting. The job of assembling and dismantling the composite forming carriage has been contracted out to the Doka formwork pre-assembly team. Summing up, Supervisor Ingolf Schneider and Foreman Bodo Seidel put it like this: “Our experience of working with the Doka composite forming carriage is very positive indeed.”

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