Infinity Tower
Dubai, UAE
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Infinity Tower, Dubai, UAE
Dubai Infinity Tower Twists for Spectacular Views
by William F. Baker1 and Bradley S. Young2
Skidmore, Owings & Merrill LLP
Chicago, Illinois
 In
a distinctive application of architectural expressions through structural
form, the Infinity Tower twists a full 90 degrees from its base
to its crown, 305 meters (1,000 feet) above the ground, through
a series of incremental plan rotations at each level. The architects
proposed the twisting geometry of the Tower as a means to maximize
the views at different elevations. Near the base of the Tower, the
Marina is the primary view. Ascending up the Tower, views to the
Gulf take precedence and the building geometry is a response to
this topography.
The 73 story cast-in-place reinforced concrete Infinity Tower consists
of 122,000 m2 (1,312,500 ft2) of residential
and amenity space, as well as 12 levels of parking including 6 parking
levels below grade. Currently under construction and scheduled to
open in 2011, Infinity Tower will stand as an iconic centerpiece
for the Dubai Marina.
The Tower is founded upon a 3 meter thick reinforced concrete mat
foundation which is supported by ninety-nine 1.2 meter diameter
bored, cast-in-place reinforced concrete piles extending approximately
30 meters below the mat foundation. The piles transfer the Tower
loads to the subgrade primarily through side friction. The subgrade
consists of loose sands and sandstone bands overlaying cemented
marine deposits and calcareous silt limestone/siltstone.
The lateral load resisting system for the Tower consists of a combination
of a moment-resisting perimeter tube frame and a circular central
core wall, connected by the two-way spanning reinforced concrete
flat plate slabs at each level acting as rigid diaphragms. This
system maximizes the effective structural ‘footprint’
of the Tower by utilizing a significant amount of the vertical reinforced
concrete for lateral load resistance.
 The
design philosophy for the Tower is based upon the exterior form
of the building as a direct expression of the structural framework.
The engineers studied a series of options for the perimeter frame
in order to create the unique twisting geometry of the Tower. Ultimately
it was determined that there were distinct advantages to stacking
the columns. Each column slopes in one direction, and is offset
over the column below, in order to generate the twisting building
form. As the perimeter columns ascend from story to story, they
lean in or out, in a direction perpendicular to the slab edge. At
every level, the columns shift in position along the spandrel beams
so that each column maintains a consistent position at each floor
relative to the tower envelope. The corner columns and the six (6)
interior columns twist as they ascend.
In order for the Infinity Tower to be realized as a viable, built
structure, the seemingly complex building form must ultimately be
derived from a structure which is easy and efficient to construct,
and which leads to practical architectural floor layouts. The system
as described above offers significant construction simplification
through formwork repetition, which directly impacts the construction
cycle time. Also, this system leads to residential floor layouts
which are repetitive at each level despite the twisting nature of
the building form.
 The
circular central core walls, which ascend purely vertically, are
cast using a slip-forming system operating through incremental but
not continuous advancement, in order to remain ahead of, but in
phase with the construction of the perimeter frame of the Tower.
The circular nature of the central core walls made slip forming
an attractive option in order to avoid the potential difficulties
in adjustment of the formwork panels towards the inside of the circular
core walls as would be the case with jump-form operations. The perimeter
concrete tube frame (columns and spandrel beams) and slabs are cast
using an interlocking metal formwork system by MFE (Mivan) Formwork.
The perimeter column stacking configuration means that the forms
are identical at each story, simplifying the formwork erection operation.
A construction cycle time of 6 to 7 days per story is consistently
being achieved
 Due
to the unique twisting geometry of the Tower, the structure has
a natural tendency to undergo additional horizontal ‘twist’
movement under gravity loads, a significant portion of which results
from the self-weight of the cast-in-place structure. Additional
movement is expected during construction and over the life of the
structure due to creep and shrinkage effects of the cast-in-place
concrete. In order to understand the potential movement of the structure,
a detailed analysis was performed taking into account the anticipated
construction sequence, and time dependent variables; such as creep,
shrinkage, and variation in concrete material properties. A comprehensive
and continuous building movement surveying program has been implemented
in order to track the behavior of the Tower during construction.
This information is used by the engineers in order to confirm the
expected behavior of the structure, and by the contractor in order
to plan for the appropriate construction alignment compensation.
Cast-in-place reinforced concrete was selected as the primary construction
material for this project primarily due to its ideal mass and stiffness
characteristics, which aid in the reduction of wind-induced movement
of the Tower, a governing factor in the design of tall, slender
towers. In addition, cast-in-place concrete is a cost-effective
and practical option for construction in Dubai.
Authors
1) William F. Baker, Partner, Skidmore, Owings & Merrill LLP,
Chicago: william.baker@som.com
2) Bradley S. Young, Associate, Skidmore, Owings & Merrill LLP,
Chicago: bradley.young@som.com
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| Owner / Project Managers:
Cayan Investment & Development
Architect/Engineer: Skidmore, Owings
& Merrill LLP,
Khatib & Alami CEC LLC
General Contractor: Arabtec Construction
LLC
Concrete Supplier: Unimix LLC &
Austrian Arabian Ready Mix
Formwork Supplier: BRM Construction
LLC &
MFE Formwork Technology (formerly Mivan Formwork)
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