Press release 2002-10-01
The 60 year old Sandö Bridge – once the world’s longest concrete bridge - in the north of Sweden is subject to major renovation. Brokk demolition robots proved ideal for the removal of the entire bridge deck when main contractor PEAB chose to try a unique and impressive method for the project.
The "High Coast", this beautiful and singular landscape, is one of the Swedish contributions to UNESCO's world heritage list. The region boasts two of Sweden's most beautiful bridges, the new suspension bridge at Veda that was inaugurated in 1997 and the Sandö Bridge, which when built in 1943 was the longest concrete bridge in the world with a single arch measuring 264 metres.
Even though the main E4 highway and most of the heavy traffic now passes over the Veda Bridge, Sandö Bridge still has a major task to perform for local traffic. The bridge is also a popular tourist attraction with its high and vivacious arch over the Ångerman River. Forty-seven metres of sailing height offer a dizzy sight from the crest of the bridge. Its total length is 810 metres.
Memories of the tragic collapse during its construction live on all too well in the area. Eighteen people lost their lives then. But as it happened just at the start of the Second World War on September 1, 1939, the tragedy was not given so much publicity. Now that the bridge is the object for the most comprehensive renovation since it was built, safety has been given top priority.
Extensive project
Repairs on the bridge commenced in the summer 2001 and are to be finished in August 2003.The Highways Authority has chosen PEAB to be the main contractor for this 115 million SEK project. The entire bridge deck, i.e. the concrete slab and supporting beams, is to be replaced. The surface is to be ripped up in stages, one side of the roadway at a time, as the bridge is being kept open to traffic during the entire project with the exception of one hour every morning.
Temporary "bridge" under the bridge
Two metres below the bridge deck a temporary platform is installed, constructed of sturdy steel beams and plank boarding. The platform rests on vertical steel beams that are anchored to the existing concrete columns of the bridge. Sections of the platform are assembled on the ground and lifted in place with a tall crane on the ground and a winch on the bridge. The whole arrangement is most impressive and it is a quite unique method that PEAB is trying for the first time.
Weight limit determined demolition method
PEAB's site manager Tommy Carlsson tells us that the first plan was to demolish the bridge deck using an excavator but the permitted load on the work platform was a limitation, especially as the bridge was also to carry the normal car and bus traffic. Norrlands Demolering AB, who was given the subcontract for the demolition work, suggested an alternative method that would be more lenient on the structure. "Weight was the biggest argument for using Brokk demolition machines", says Kenneth Åhlin, MD for Norrlands Demolering, "but their flexibility is an additional advantage. The Brokk machine is easy to turn around in these confined spaces so that it can operate on both sides of the lane".
Norrlands Demolering uses three Brokk 250 and one Brokk 180 on the project. Ripping starts from the outside edge of the roadway inwards. Once the bridge deck has been demolished, the outer and centre concrete beams on one half of the road must be cut away (there is then only the outer beam left on the other side of the road as the centre beam is common to both sides) and finally the crossbeam supporting the deck at each bridge pier. One such "compartment" between the piers is around 15 metres in length and demolition advances at about one compartment a week. The total demolition volume is 3,500 cubic metres solid concrete, which is the equivalent of around 6,000 cubic metres loose concrete. The concrete proved to be of shifting quality due to the many repairs and patching that has been carried out over the years and which according to Kenneth made it especially difficult to assess the time needed for the demolition work.
Rebars are separated, the demolition rubble is collected on plates and loaded into boxes to be lifted off the bridge by the crane. The demolition rubble is taken directly for landfill or destruction.
"We've had long experience with Brokk equipment", says Kenneth Åhlin. "We have ten machines of various models, the oldest is about 15 years old. They are extremely reliable and can stand hard use."
PEAB has estimated that around half the bridge will have a new superstructure by the end of October. Once the entire stretch is finished, the temporary centre barrier must be dismantled and the roadways cast together. The bridge piers must also be inspected and repaired wherever necessary and given a new surface of sprayed concrete.
The Sandö Bridge can then continue impressing passers by and residents with its daring arch and grandiose view.
Norrlands Demolering AB in Sundsvall is an employee-owned company founded in 1999 when personnel acquired the operation from Skanska-owned Stabilator. The company has 17 employees and is mainly active in the northern and central parts of Sweden.