Work on the 490m span cable stay section of the resund crossing between Denmark and Sweden has passed a crucial milestone. Sundlink Contractors positioned the first main span steel truss section last Thursday and its back span neighbour at the weekend.
Girder lifts at resund are inevitably delicate because of the size of the elements and the tight constraints of the pylon geometry. The main span girder lifted on Thursday, and its back span sister, are both 140m long and each weighs 6,150t.
One end of each section had to be squeezed between the legs of the pylon - with just 150mm to spare on either side - so that the tip could rest on the cross beam. The other end of the main span section now rests on a temporary steel prop standing on pad foundations on the shallow seabed. The back span section lifted at the weekend now forms a bridge between the pylon and its nearest approach viaduct pier.
Sundlink used the floating crane Svanen - veteran of Storeblt and Prince Edward Island Bridge - to ship the sections from Malm at the Swedish end of the project to the pylon. 'Svanen is equipped with eight anchors plus winches, and everything is controlled by joysticks,' said Sundlink project manager Ove Lauritsen.
At the site, the Svanen dropped anchor and its operator used his joystick controls to haul the crane
into position before lowering the span sections.
Sundlink had scheduled the first lift to take 48 hours, allowing for delays caused by poor weather.
In the end. the lift took just 16 hours thanks to calm seas and light winds.
Cable stay span erection at resund is unusual as shallow seas and wide shipping lanes have made it easier to use temporary props to support the 140m long sections until they are tied in to the cables.
Often, deck sections for these bridges are kept shorter so they can be attached to the cables immediately and obviate the need for props. This usually happens on crossings where deep water or narrow shipping lanes rule out the use of props. At resund, the shipping lanes are wide enough for vessels to be routed away from the props.
Once the newly positioned sections are cabled up, the temporary prop will be moved and made to support the next main span element. When the first two sections for the eastern half of the main span are in place, Sundlink will take the prop across to the western pier to support girder erection on the other half of the bridge.
Sundlink's fast track construction programme means that cable installation will start immediately, even though work on the pylon is still under way. The western pylon is further behind after running into problems with concrete mixes. But these delays are not expected to affect girder erection on the western side as this is not scheduled to start until the turn of the year.