The world's tallest twisting tower—the 75-story, 1,010-foot-tall Cayan Tower in Dubai, which rotates a full 90 degrees from base to top—is a monument to rational thought in the service of art and commerce. Rational thought, because the architects and engineers at Skidmore, Owings & Merrill (SOM) worked systematically to construct the building with regular components and repeating floor plans. Art, because the building presents itself as a freestanding sculpture visible from across the Dubai Marina. And commerce, because the greatest virtue of repeating floor plans is that they streamline the process of selling the building's 495 condominium apartment units, which range from studios to four-bedroom duplexes.
Some other recent twisting skyscrapers, such as MAD Architects' Absolute Towers outside Toronto, rely on a conventional (non-twisting) column grid to support the rotated floor plates, resulting in sometimes awkward column locations and a welter of differing plans. But SOM's client, Cayan Investment and Developers, did not want to give up the economies of standard interior layouts and unitized curtainwall construction. No columns in funny locations, no irregular façade openings allowed. The trade-off, however, was greater complexity in the structural design.
Each floor rotates 1.2 degrees around a cylindrical elevator and service core, which consulting partner George Efstathiou, FAIA, likens to a vertical "spindle" at the building's center. In order to keep the interior layouts consistent, the SOM team—led by design director Ross Wimer, FAIA, who recently left the firm—looked at several ways to rotate the reinforced-concrete structural columns of the Cayan Tower in tandem with the floor slabs. One option was to make all of the columns tilt and twist—like spiraling lines on a giant barber pole. That option was rejected, explains SOM's structural engineering partner William Baker, because, over time, it would have made the structure vulnerable to damage from additional twisting by gravity, known as "secondary twist." The other problem was that, "you can't have sloping columns and have mass-produced wall panels," Efstathiou says.
The team's solution was to differentiate between columns leaning to the side and leaning forward or back, relative to any given elevation of the building. By eliminating sideways incline in all but the building's internal columns and corners, they gained greater stability and rectangular façade bays. The roughly 3,000 perimeter columns stand perfectly vertical—when seen from the front or back, that is—and "step" between 12 and 14 inches to the side with every floor level. The stepped columns transfer their load through a concrete slab that works like a pile cap. Seen in side elevation, however, the perimeter columns lean forward or back by as much as 10 degrees to meet the shifted floor slabs above and below. The width, angle, and spacing of columns looks the same from floor to floor, even as the floors themselves shift slowly, as they progress higher, around a quarter circle. In fact, the same formwork was used for the columns on each level, with only slight modifications to account for diminishing load toward the top. Such economy of means defines the tower's design and engineering, which, given its unusual structural needs, became an epic exercise in "simplifying complexity," Baker says.
The structure's movements were monitored before, during, and after construction to ensure that they stayed within expected limits, since the secondary twist problem was much reduced, but not eliminated, in the final design. Baker says that the Cayan Tower's wind performance will be at least as good as that of a comparably high, non-twisting tower. In fact, wind-tunnel tests predicted that the tower's twisting profile would scatter the flow of wind around it, reducing its sway during desert windstorms.
The tower's rotation also created a plumbing challenge for the M/E/P engineers Khatib & Alami (also the project's architect-of-record). How to organize the plumbing system when the bathrooms and kitchen keep moving? Water and sewer pipes run from each apartment to the outer ring of the building's central core, then run vertically down the few paths not obstructed by ever-shifting apartment doors.
Look closely, and you'll see that two sides of the Cayan Tower are subtly inflected, so that each floor plan reads not as a pure rectangle but as a faintly chevron-shaped hexagon. "There is a little bit of a kink put in just for architectural interest," Efstathiou explains, adding that the indents enhance the apparent slenderness of the building from afar. The tower's contours seem to taper and swell depending on the angle from which it is viewed. From head-on, it displays a torquing bulge in the middle; seen from an oblique angle, the building takes the form of an hourglass.
There is nothing particularly innovative about the tower's glass-and-aluminum curtainwall system—but perhaps that is the point, since the use of standardized, rectangular components (measuring roughly 82 by 124 inches each) is an achievement in itself. Some of the relatively transparent low-E glass is veiled by perforated aluminum screens. These one-story-high, silver-painted panels stand 4 inches off the glass, come in two widths, and are 30 to 60 percent open. Taking a cue from traditional Arabic mashrabiya latticework, they defray the desert sun and give a nod to regional customs of privacy. However, the screens have been so thoroughly value-engineered since SOM won the 2005 competition—for what was originally called the "Infinity Tower"—that they little resemble the dancing pattern of solids and voids from the early drawings.
Still, the undistinguished surface qualities of the Cayan Tower are secondary to its powerful geometric presence, a mighty twisting prism. The purity of the building's sculptural profile is all the more striking when you consider that it has hundreds of balconies—all tucked stealthily into the recesses created by pulling the curtainwall back from the outer screens. Just another example of the hidden design work required in a project that began by twisting the rational, and ended by rationalizing the twist.
Project Cayan Tower, Dubai, United Arab Emirates
Client Cayan Investment and Development
Architect Skidmore, Owings & Merrill (SOM), Chicago—George J. Efstathiou, FAIA (consulting partner); Ross Wimer, FAIA (design director); Brett Taylor, AIA (project manager); Jo Palma (senior design architect); Anwar Hakim, AIA (senior technical coordinator); Daniel Salinas, Eric Zachrison, AIA, Hunsang Lee, Inho Rhee, AIA (design architects)
M/E, Civil, and Structural Engineer SOM, Chicago
Construction Manager Currie & Brown
General Contractor Arabtec Construction
Landscape Architect SWA Group
Lighting Designer Fisher Marantz Stone
Water Features AquaFountains International
Wind Tunnel Testing Boundary Layer Wind Tunnel Laboratory
Acoustics/Audiovisual/IT Cerami & Associates, Shen Milsom & Wilke Architecture/Engineering Khatib & Alami
Vertical Transportation Lerch Bates & Associates, Van Deusen & Associates
Life/Fire Safety Engineering Rolf Jensen & Associates
Security Sako & Associates
Size 7.75 million square feet