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A new 830 m long cable-stayed bridge is being built across the River Vistula just south of Warsaw’s Old Quarter, with twin towers to support and stay its 33 m wide carriageway deck, which has a 250 m span. The contract to supply the formwork for the two slender, 92 m tall bridge-towers went to Doka Polska.
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Forming bridge-towers such as these cost-effectively is a fascinating challenge: Massive springers, inclined towards the outside at an angle of 75° to the perpendicular and conically tapering as they rise. Then, at a height of 12 m, a pre-stressed concrete cross-beam to support the carriageway decks. Above this, two slender piers: Up to a height of 62 m, these are hollow boxes and are inclined inwards at an angle of 7°; above the 62 m mark, they rise exactly in the perpendicular. At the kink in the piers at a height of 62 m, there is a second cross-beam.
Remarkably small quantities of equipment, most of it from the standard product range – this is the secret of optimum cost efficiency here. In order not to have to use heavy special profiles on the piers (which had to be formed without using form-ties), the walings of the Top 50 elements were stiffened with trusses. One set of springer formwork, assembled from Top 50, was used to form the bases of all four piers in succession.
Four sets of Top 50 formwork were then “climbed” on MF 240 climbing platforms to form the four rising pier shafts, in 17 casting sections up to the finished height of 92 m. All this was done with only a very few crane cycles and – in the inclined sections – with a special overhang lifting unit, supplemented by a single-sided inside formwork in the hollow-box zones.
The four sets of formwork continued to be used without any modification above the top kink, where a 27 m long hollow steel profile had to be embedded inside each of the pier shafts.
The Top 50 formwork for the bottom cross-beam rested safely on a truss made of 20 tonnes of steel profiles, which was used a total of four times: First for the two bottom cross-beams, and then for the two top ones.
As the exemplary concept employed here clearly shows: With good planning, even out-of-the-ordinary challenges can be mastered both economically and in record time.
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