...with horizontal and inclined tubes. These tubes reach back to 4.5-tonne-steel anchorages embedded in shear walls at the building’s back corners.

While the spine column takes perimeter vertical loads, the exoskeleton around it provides wind resistance and dampens the building’s vibrations, according to Calatrava.

To build the tower, HSB set up its own construction management team with most of its 13 staff on loan from NCC. That arrangement is separate from NCC’s $30- million superstructure job, which does not include the $9-million exoskeleton.

NCC’s site work, starting in April 2002, reached the concrete roof last month. Mostly thanks to wind, the main structure is about three months late, says Nordgren. Apart from wind, the main challenge was the tower’s height, especially pumping the concrete more than 180 m up, he says.

NCC pumped from the ground at a rate of one floor every eight to nine days, says Nordgren. It cast the solid concrete floors in some 20 pours each. For the core and its internal walls, NCC used self-climbing formwork. Core formwork rose in a single assembly, five floors deep. While in one position, the assembly allowed construction of the core on one level and on internal walls over three floors below, plus follow-up work, adds Nordgren.

With formwork being dismantled, NCC will build the top three levels of core interior walls out of precast concrete. This should finish up in mid-January, says Nordgren. But that assumes the wind cooperates. Considering work was halted again late last month due to wind, the end date is not firm.

NCC’s delays have bothered the exoskeleton erector, Denmark’s Promecom A.B. Fredericia. The eight-person team has been hampered a few times, returning to Denmark for four weeks on each occasion, says project manager Karsten Rasmussen.

Promecom joined the project late, in November 2003, after HSB had a falling out with its original erector. Spanish contractor Elaborados Metálicos S.A (EMESA), Coruña, was meant both to fabricate and erect the 900 tonnes of exoskeleton. But the contract "has been a disaster," says Ingvar Nohlin, HSB’s project director. His big complaint is about "quality problems with the welding."

EMESA retained fabrication work and completed steel delivery this summer. But a dispute over payments with HSB is under arbitration, says Nohlin.

EMESA officials were not available for comment. But Calatrava says the contractor is "a very correct firm and very advanced." It has worked on previous Calatrava jobs and is involved in the current erection of the railroad station for Liège, in Belgium.

Early Momentum

For Promecon to gain early momentum on its hurriedly awarded $2.3-million erection contract, "everything in the first six weeks went very fast," says Rasmussen. Promecom used three mobile cranes to lift steel at low levels. A winch arrangement raised remaining steel from inside the rising concrete frame.

If wind allows, the last piece of exoskeleton will be placed by the end of December, a couple of months late, says Rasmussen. However, shell and core is off the critical path, says Nohlin. With time to gain during the fit-out, he still plans for a July opening.

The tower will be the landmark structure for the small Swedish city that has grown in stature since the Øresund fixed link with the Danish capital opened four years ago. Nohlin concedes that an ordinary building may have been more economical for HSB, which is a housing cooperative. But he says that if HSB had wanted a conventional design, it would not have asked Calatrava to do it.