Dubais Infinity Tower, a 72-story skyscraper designed by Skidmore, Owings &

Merrill (SOM), began construction in 2006 and is finally nearing completion this year.
The major characteristic of the tower is the way it twists up into the sky, as each
floor is rotated 1.2 to create a full 90 twist from bottom to top.
SOM designed the Infinity Tower with the same mindset as the Willis Tower (Sears
Tower), John Hancock Center, and Lever House: in order for a building to endure, the
exterior form must be a direct expression of its structural framework. The powerful helix shape
created by the rotating floors emphasizes SOMs design philosophy and utilization of cuttingedge techniques. SOM shows the great power of design through Infinity's unique spiral shape
that reflects the ever-changing shapes of the deserts, winds, and seas that surround it.
One challenge that SOM had to overcome with Infinity Tower was how to efficiently control the
intense desert heat. The winding shape reveals a structure that helps protect its interior from the
sun. In addition, its reinforced concrete structure is clad in metal panels and screens to provide
additional shade from the intense heat.
The tower will serve a variety of purposes including luxury residential units, parking, and retail.
The twisting form optimizes low level views to Dubai Marina and high rise views to the gulf and
city. Its unique, high-strength structure maximizes its views while maintaining the views of the
neighboring buildings.
Infinity's unique form and prime location will make it one of the most recognizable buildings
in Dubai. Although other helix-shaped buildings exist, Infinity will be the tallest twisting tower in
the world.

Project Credits
Project Cayan Tower, Dubai, United Arab Emirates
Client Cayan Investment and Development
Architect Skidmore, Owings & Merrill (SOM), ChicagoGeorge 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
Cost Withheld

BUILDINGS
November 19, 2013 3

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Cayan Tower, Designed by Skidmore, Owings & Merrill

Cayan Tower, Designed by Skidmore,

Tim GriffithOne of the main reasons for Cayan Towers iconic twist was to
maximize residents views across the Dubai Marina and the nearby Palm
Island.
The world's tallest twisting towerthe 75-story, 1,010-foot-tall Cayan Tower in
Dubai, which rotates a full 90 degrees from base to topis 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 faade openings allowed. The trade-off, however, was greater
complexity in the structural design.

The twist also creates a variable silhouette. From one angle, the tower
appears hourglass-shaped, from another, the middle floors appear to bow
outward.
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 teamled by design director Ross Wimer, FAIA, who recently left the
firmlooked 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 twistlike 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.
Tim GriffithThe floor plates are not the only things that were optimized for
regularitybecause the floor plates are rectilinear, the curtainwall system was
able to be unitized into repeatable modules over much of the 75-story building.
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 faade bays. The
roughly 3,000 perimeter columns stand perfectly verticalwhen seen from the
front or back, that isand "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.
Tim GriffithBy the time the tower officially was opened in June, 80 percent of
the units had reportedly been sold, though interior fit-outs were still in
progress.
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.
Tim GriffithHundreds of balconies are hidden behind the mashrabiya-inspired
screens of the tower's unitized curtainwall system.
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 headon, 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 systembut 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, silverpainted 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 competitionfor what was originally called the "Infinity Tower"
that they little resemble the dancing pattern of solids and voids from the early
drawings.
Courtesy Skidmore Owings & MerrillCurtainwall detail rendering.
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 balconiesall 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.