Exoskeleton. Pipes spin up and around Western Europe’s tallest residential tower. (Photo courtesy of Promecon)

With perimeter walls that both "swirl" and cut back to the core, the 26,000-sq-m tower in Malmö, already a landmark, has demanded some highly tailored vertical supports. Yet despite the tricky geometry, wind at the coastal site has been the contractors’ biggest gripe. The gusts have caused delays in both concrete work and, after a difficult beginning, erection of the steel "exoskeleton."

Calatrava, recently named the 2005 Gold Medal winner by the American Institute of Architects, gets credit for the tower’s shape, but the vision to apply it to a building is claimed by the owner, HSB Malmö. HSB, was so inspired by a picture of Calatrava’s "Twisting Torso" sculpture of a human, that executives called the architect and eventually hired him.

During design, the sculpture served as a physical model, reassuring HSB that the building would be "aesthetically coherent," says Calatrava, from his office in Zurich.

Spiraling. Concrete superstructure turns 90° from bottom to top of 190-meter-tall building in Sweden. (Photo courtesy of HSB Malmo)

Construction accounts for about half the $235-million cost. The tower rises out of a two-level basement enclosed by a 30-m-dia cylindrical concrete wall. Its base slab reaches more than 6 m down to limestone, obviating need for piling. Above ground, the structure turns around a spine-like core as it rises. An exoskeleton of white steel tubes embraces the glassy "front" facade.

Each of the building’s 54 floors is turned by about 1.6° relative to the one below, so that the whole tower twists 90° from bottom to top. The concrete structure rises 184 m, centered on a cylindrical core with an internal diameter of 10.6 m and walls varying in thickness from 2 m at the base and 40 centimeter near the top.

Tower floors are shaped roughly like an arrowhead. Three of their five perimeter walls are 17 m long, slightly curved, and set some 5 m from the core. The other two project out to form a triangular floor area, its tip 10 m from the core. Click here to view images

Full-height curtain walls enclose the two facades of the triangular area. The other three faces are arranged in five-floor-deep "stacked" modules with walls perforated by windows. There is a 2-m-deep gap between each module, from the perimeter to the core. The gap exposes the core like the backbone of a human, explains Christian Brändle, Calatrava’s project architect. Click here to view floor plan

Because the modules’ perimeter walls are not vertically continuous, full-height perimeter columns are not possible. Instead, in each module, the lowest slab cantilevers from the core to support floors above with 11 slim, steel columns hidden in perimeter walls. While floors are 27 cm thick, the lowest slab of each module is 90 cm thick at the core, reducing to 40 cm at its edge.

Propped

With no primary columns in the curtain walls, the triangular floor areas are propped only at their tip by a concrete perimeter column that gradually spirals to the ground within the building envelope. The roughly 60-cm-wide multifaceted column is heavily reinforced with about 100 kilograms per cu m of rebar, says Bjorn Nordgren, project manager with concrete contractor NCC Construction Sverige A.B., Solna.

The stark exoskeleton around the building’s front face is made of tapered white steel tubes with diameters up to 90 cm. Following the concrete perimeter column, the exoskeleton’s single upright is fixed to the tower between each module mainly...