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The suspension tower will reach a soaring 200 metres overall, and the first 175 metres are a challenging truncated-cone geometry in CIP concrete. Up to the 98-m level the tower features a centre incision, scissoring down to ground level in two legs. Each of these legs is characterised by a nearly semi-circular cross-section and both are being climbed in 21 concreting sections with the Doka high-performance SKE100 automatic climbing formwork. The cross-section tapers significantly as the tower rises and the structure itself is geometrically challenging, so the automatic climbing formwork was designed by the specialists at the Doka Expertise Centre for Automatic Climbing Formwork using a detailed 3D solid model and making full allowance for the efficicent economics of the overall solution. The self-climbing formwork and the Doka Top 50 beam formwork have to adjust easily and quickly to the continuous taper of the structure’s cross-section, so the climbers are designed for maximum adaptability. This is the reason why the climbing platforms are carried on rollers on the outermost climbing brackets. This allows for relative movement between the outermost brackets and the climbing platforms, so the brackets follow the taper of the suspension-tower legs without further adjustment. The bogey units carrying the large-area Top 50 beam formwork assemblies can be moved on special rails along the climbing platforms and precision-adjusted quickly and speedily to suit the changing radius. "This solution puts us in a position to adjust the formwork easily and without loss of time to suit the changing geometry of the structure. The cross-section tapers severely but even so we need only two sets of formwork to take us up the first 21 concreting sections: that makes for a tremendous saving on cost of materials", asserts Porr project manager Patrick Wagner when asked about the benefits of this fit-for-build automatic climbing solution. A step 50 cm deep on the inside of each tower leg will be the carrier for the superstructure, but this challenge too is easily handled by the SKE100 automatic climbing formwork. There are also two narrow supply shafts rising inside each leg, and they join and continue on up as a single shaft from the waist where the two legs meet. Shaft width is a mere 1.20 metres, so here again tailor-fit shaft formwork from the Doka Ready-to-Use service has proved the key to success, this time combined with the Framax stripping corner I. This arrangement allows the spindles for backing off to be operated from above, and then the formwork is ready to be crane-lifted into position for the next pour.

Trouble-free climbing for smooth progress

Space is at a premium as the two legs come closer, so from the 13th concreting section on up the formwork on leg 1 climbs up to three sections ahead of its counterpart on leg 2. The leg-1 formwork is removed after the 22nd concreting section so that the formwork on leg 2 can complete its climb unhindered. Each automatic climbing formwork assembly incorporates a follow-up platform so that the requisite finishing work on the concrete surface can be conducted to maximum efficiency. Safety, of course, is all-important, so all platforms have enclosing protective railings and full-enclosure site netting as well. Access is by integrated ladders complete with cages and self-closing trapdoors. A walkway spans the gap between the two legs, joining them to permit speedy and safe movement from one workplace to another. In this way it is possible to cross in safety to a platform on the opposite climbing scaffold at any time during the formwork phase of construction. The SKE100 platforms were assembled on site by the construction crew under the professional supervising eye of an experienced Doka site foreman. The support of the Doka site foreman in the start-up phase, moreover, contributed much to the smoothness with which forming got under way and so to speedy progress right from the very first concreting section on. The Top 50 large-area panels were preassembled in the Doka Belgrade branch and delivered JIT and ready to go, streamlining on-site logistics. From the point at which the two legs join, the suspension tower is climbed as a narrow tapering truncated cone with the newly developed SKE50 plus automatic climbing formwork. The tower’s diameter slims from 9.50 metres at the 22nd concreting section to 4.00 metres at the 39th. Eight platforms are arranged in a radial configuration with integrated adapters so that the assembly adjusts as the cross-section tapers.

The suspension tower is slim and tapers severely as it rises; it is being erected with Doka’s SKE100 and SKE50 plus automatic climbing formwork.

The formwork repositions effortlessly so it adapts quickly and easily to the structure’s changing cross-section.

Special solution for the technological challenge of incremental launching on this bridging project

The southern section of the bridge (back span) is 200 metres long. It is divided into 18 concreting sections and has a roadway slab 45 metres wide to carry ten lanes of traffic. The slab cantilevers out 12 metres to each side of the three-cell box girder. The two outer cells of the supporting structure are each two metres wide and are being cast with Doka forming carriages based on Top 50 beam formwork. Planning for this inner formwork had to allow for two large internals per section: these are the anchorages for the cables that will later stay the bridge. This is why the two forming carriages divide horizontally along a split-line, so that the two halves can be separated and manoeuvred easily past these internals. The forming carriage for the main cell, 8.50 metres wide, is also made up of Top 50 panels, with Staxo 100 frames as propping. This carriage has to pass over palisters in the bottom slab that are partially solid-cast, so the Staxo frames are fitted with load spindles. The spindles retract up to one metre so that the frames can be stepped past these obstructions. A major design challenge on this demanding project is the 12-metre cantilever of the roadway slab on either side of the box-section girder. Steel struts set at 4-metre centres give the structure the added rigidity it needs. These solid steel struts are footed into the formwork at the ends of the roadway slabs and welded to the box girder. The cantilever-arm formwork is a two-part construct with a swivel mechanism for simple and safe forming up and stripping out. At these stages of the process the formwork is lifted and lowered by crane. "This formwork solution was planned down to the last detail and fine-tuned for maximum cost efficiency and here on site it proved itself totally, coming right up to and even exceeding even our high expectations", states project manager Mario Perissutti in his intermediate summing up of progress to date.

The southern section of the bridge is 200 metres long and is being built using the incremental launching technique. Made-to-measure formwork solutions from Doka are in place to ensure speedy progress on the build, combined with optimised material utilisation.