Sundsvall Bridge sections’ maritime challenge
There’s no doubt that the Sundsvall Bridge, Sweden, is going to be striking.
However, the apparent elegance is belied by the massive construction. It is using around 23,000 tonnes of steel, plus 35,000m3 of concrete with 5,000 tonnes of reinforcements.
It can’t be denied that although technological capability has soared, so has ambition, and in Europe these large public developments have become more and more architecturally demanding. After all, this kind of construction can dominate a landscape.
So there’s a lot of competition involved in a project that’s not just going to fit the bill, but also be outstanding. Even beautiful. And this of course means that the winning designs are going to pull out all the stops on innovation.
In the case of the 2,420m long road bridge over the Gulf of Bothnia designed by KHR Architects, the bridge’s sweeping curves have demanded a technical tour de force from everyone involved, especially steel structure specialist Max Bögl Steel working under the Sundsvallsbron Joint Venture of Max Bögl International SE, Strabag Wasserbau.
There are 11 bridge sections all in all. The first and last of these (one and 11) are the grounded steel segments which have already been erected onsite and integrated with the groundworks.
However, the other nine segments are being constructed remotely in Poland. These rest on sheet piled structures acting as cell-type cofferdams with piers topped by a V-shaped steel lattice work which helps to take some of the impact out of the pounding the bridge will get from its traffic.
It’s being planned so that the biggest span across the fairway below gives an air draught of 33m and a clear width of 90m. These are large enough distances to provide a challenge but, added to this, the award winning design brings its own challenges.
The steel components that make up the 1,420m long main span are of a torsionally rigid hollow box construction that can vary between around 3.5m and 6.5m in height. Despite coming to 23,000 tonnes in all, not one of these cross sections is like another and yet, all have to be precision engineered.
Shaped like a ‘C’ that curves between the two banks of the Gulf, the sections also narrow toward the centre, running from 38m across to 27m, explains Stephan Lüttger, project manager for Max Bögl. He adds that despite the variations “we try to do a ‘line’ production where we can, replicating as much of the process as possible” in order not to be swamped by a task that’s both Herculean and incredibly detailed.
So, a specially developed automated production line at Sengenthal, located just north of Munich, fabricated the smaller elements which were then transported via the Rhine-Main-Danube Canal to Rotterdam in a massive ‘caravan’ of 45 inland cargo boats.
Some went directly to site to form the ‘end’ sections, while others went on, via 36 cargo vessels (mostly sourced from the Wilson stable), to Max Bögl’s assembly facility in the port city of Szczecin, Poland. Here these precision cut elements are being brought together to form larger modules. The first of these steel mid sections to be manufactured was section number 10, measuring 117m long and 35m wide and weighing in at a massive 1,900 tonnes.
Section 10 was loaded at Szczecin onto a floating pontoon. Maarten Brasser, Seacontractors’ manager for Towage and Offshore explains that loading from Max Bögl’s Polish fabrication yard, two skidtracks extend out over the river. Winches are used to pull the 100m Seacontractors transport barge Veka 3303 into position below the section after ballasting. Lifting is simply done by pumping out the ballast and letting the barge rise under the module. But it’s still tricky he explains “as the distance between the skidtracks is only 102.6m, which only leaves 1.3m of clearance at both ends of the barge”.
This left section 10 to be towed across the Baltic by Seacontractors’ deep sea tug Dutch Power.
On arrival some ten days later, the tandem lift operation started. “You might assume that the bridge sections would be installed from pylon to pylon, but each section extends 40m over the pylon on one side”, says Mr Brasser.
So, on one side is Max Bögl’s own lifting technology which sits on the previously constructed bridge head, a special innovation developed by the company to incorporate two 650 tonne strand jacks which help to pull up one end of the new bridge section from the tethered pontoon.
The other side of this first lift was carried out by the powerful Matador III floating crane, the role being taken over by Sarens’ Twinbarge for later sections. Mr Brasser explains that before the bridge section is installed, first the pillar has to be topped by the steel pylon-like structure, using the fixed crane boom on the pontoon lifting tower.
Taking 17 hours, the deployment of section 10 started at noon and continued all night, with everyone relieved when, at 05:00 in the morning it was finally in place. “A very, very long day”, concluded Mr Lüttger.
There’s now a steady stream of bridge modules underway from Szczecin, and the rest, including the two largest sections will be arriving on site ready to take their place in the construction in relays. December will hopefully see the final mid-section being brought into place.
By Stevie Knight
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