SF OneKingWestTower June08

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STRUCTURE magazine June 2008
34
of view within this extremely narrow project
site in the middle of an urban financial
district. The overriding concern during
design for all these technical design issues
was the building’s 26-foot (at its narrowest)
East-West dimension.
The lateral system ultimately chosen for
this building was a typical concrete shear wall
with some unique structural innovations
that were implemented in selected locations.
The first innovation was to use outrigger
concrete walls at the lower levels (Floors 14
though 16) supported on jumbo outrigger
structural steel columns. These steel columns
were subsequently embedded with surgical
precision through a portion of the existing
Dominion Bank building. This maximized
the width of the building at its base to just
over 46 feet, reducing the overall building
slenderness to just over 13:1, still large, but
more economical. While this expansion of
the overall lateral force resisting system base
width was helpful, tremendous uplift forces
remained and needed to be resisted within
the building foundations.
To counter these large uplift forces, the
main foundation for the tower consisted of
a 3-foot thick concrete strip footing grid-
work that included over 100 rock socketed
Background
One King West Tower is situated in the middle of the busy
downtown business district in Toronto, Ontario, Canada.
The tower sits on a small compact site adjacent to the
Dominion Bank building, an architectural stalwart of the
city built in 1914. Because this historic structure was to form
part of the new tower, and because the remaining open site
was limited to just over 26 feet wide, the location demanded
innovative solutions and approaches throughout the design
and construction process. This extremely thin piece of land
had to support a tower program that included over 500,000
square feet of supported floor area, 570 luxury residential
suites, and 100 parking spaces. Stanford Downey Architects
was charged with not only making this space elegant and
inspiring, but also to have a profound impact on the Toronto
skyline. The property owner’s goal was to attract high profile
clients with a taste for grandeur. Working closely with the
Halcrow Yolles structural engineers, and after many months
of design coordination, an innovative structural system was
devised that enabled a new, slender tower to merge with the
existing Dominion Bank Building.
Inspired Innovation: The Slender Tower
The result of many design meetings was a 610-foot (measured
from foundation to rooftop) high residential concrete tower
that is sandwiched between the Old Dominion Bank building
and the adjacent property. To accomplish this height, the tower
slenderness ratio (total height divided by width) would need
to be around 23 at its narrowest width. This slenderness ratio
is arguably one of the world’s largest for a high-rise building at
the time construction began.
The biggest challenge for the structural engineers was
to design a lateral resisting system that would meet this
slenderness ratio and satisfy the base overturning forces, drift
due to wind loads, comfort acceleration criteria, and also keep
the building economically feasible from a construction point
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One King Wet Tower
The task of successfully merging historical grand décor with sleek modernism is a
challenging one. One King West Tower in Toronto, which marries the historic to the
progressive through technical innovation and functional inspiration on a grand scale, is
an example of how that challenge can be met to create a striking landmark structure. One
King West Tower merges the turn of last century’s stone masonry Dominion Bank Building
with a slender, contemporary high-rise, concrete tower. The award winning, mixed-use
residential structure in 2005 became the tallest residential building in all of Canada.
By Agha Hasan P. Eng et al.
The One King West Tower is 51 stories of private luxury condominiums located
in the central business district of Toronto, Ontario, Canada. The tower was
constructed integrally with the Dominion Bank building in the foreground.
Courtesy of
©
Drew Hauser.
The finite element model
for One King West Tower
under gravity and wind
sway deformation. The
color changes denote
different concrete strength.
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STRUCTURE magazine June 2008
35
Construction of the liquid tuned dampers at
the top of One King West Tower.
anchors drilled to a depth more than 30 feet into rock. More than 50% of these
anchors (including all of the anchors installed within the existing Dominion
Bank building) were pre-stressed into place in order to activate them to resist uplift
even during construction.
Next, engineers performed a rigorous finite element model of the tower concrete
shear wall lateral system. Historically, tall buildings exhibit “cross wind” effects
that magnify the short direction dynamic properties and wind sway of a building.
However, for buildings with large planar aspect ratio, the cross-wind vortex shedding
along building length is poorly correlated due to wind flow reattachment. This was
confirmed in wind-tunnel analysis which concluded that the along-wind buffeting
governs the vibrational response of the building
Through years of experience with high-rise design, Halcrow Yolles engineers
have developed proprietary design aids in order to calculate the loss of stiffness in
concrete shear walls under the combined effect of wind and gravity loads. Using
these relationships, the engineers on One King West Tower diligently calculated
stiffness loss at every level and applied these values when analyzing the building
under gravity loads, lateral loads, and dynamic effects. Because gravity load
sway played a major role in building lateral displacement, different wall cracking
parameters had to be adopted for easterly and westerly winds. This resulted in
creation of two independent models for wind and gravity load analysis for easterly
and westerly wind cases.
One King West Tower under construction.
High-rise buildings must also be evaluated
for occupancy comfort when undergoing
wind induced oscillations. This is done by first
modeling the dynamic properties within a finite
element program, then verifying these dynamic
properties with wind tunnel testing. One simple
method of determining occupancy comfort
is to measure the acceleration at the top floors
of the building under the worst wind induced
dynamic condition. Usually an acceleration
value under 15 milli-g is considered acceptable
for residential buildings. For One King Street
Tower, along its narrow East-West dimension,
the accelerations were originally reported to
be as high as 17 milli-g by the wind tunnel.
In order to reduce the accelerations economi-
cally, Halcrow Yolles along with Boundary
Layer Wind Tunnel Laboratory (BLWTL) im-
plemented a tuned liquid damper that was
installed at the top of the tower. This damper
used water filled tanks to a specific height
within roof-top concrete tanks to counter the
wind induced dynamic effects. The tuned
liquid tuned damper (TLD) may be tuned to
the individual building frequency of concern by
adjusting the height of the water in the tanks.
For buildings in this acceleration range, for
which wind resonant effects are substantial, the
implementation of dampers may lead to overall
wind force reduction, and corresponding
savings in material building costs. Further
evaluation of tuned liquid tuned dampers are
being monitored under a long-term plan aided
by a Canadian government grant.
continued on next page
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STRUCTURE magazine June 2008
36
The shear wall outrigger connection detail.
This detail shows how Halcrow Yolles
engineers connected the interior concrete
core walls to the exterior steel columns
that were surgically placed within the Old
Dominion Bank Building.
W460x82 C
L
STEEL COLS BELOW
WELDABLE BARS
WELDED TO
W-SECTION FLANGE
SHEAR STUDS
10
WELDABLE BARS WELDED
TO ANCHOR PLATE
ANCHOR PLATE
PLATE EACH SIDE OF W-SECTION
WEB WIDTH TO MATCH
W-SECTION FLANGE
45°
CONT
STIFFNER PLATE WELDED ALL
AROUND TO COL SECTION EACH SIDE
STEEL COLUMN
ANCHOR PLATE
12
DEFORMED ANCHOR BARS
WELDED TO W-SECTION FLANGES
SHEAR STUDS AT MID-DEPTH
EACH SIDE OF W-SECTION WEB
FIN
FLOOR
LEVEL
ELEVATION
PLAN
CONC WALL ABOVE
SHEAR-
STUDS
WELDABLE
BARS
C
L
CONC WALL
ABOVE
WELDABLE BARS EQUALLY-SPACED
EACH SIDE OF W-SECTION WEB,
WELDED TO ANCHOR PLATE
WELDABLE BARS 3 EQUALLY-SPACED
EACH SIDE OF W-SECTION WEB,
WELDED TO ANCHOR PLATE
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W460x82 C
L
STEEL COLS BELOW
WELDABLE BARS
WELDED TO
W-SECTION FLANGE
SHEAR STUDS
10
WELDABLE BARS WELDED
TO ANCHOR PLATE
ANCHOR PLATE
PLATE EACH SIDE OF W-SECTION
WEB WIDTH TO MATCH
W-SECTION FLANGE
45°
CONT
STIFFNER PLATE WELDED ALL
AROUND TO COL SECTION EACH SIDE
STEEL COLUMN
ANCHOR PLATE
12
DEFORMED ANCHOR BARS
WELDED TO W-SECTION FLANGES
SHEAR STUDS AT MID-DEPTH
EACH SIDE OF W-SECTION WEB
FIN
FLOOR
LEVEL
ELEVATION
PLAN
CONC WALL ABOVE
SHEAR-
STUDS
WELDABLE
BARS
C
L
CONC WALL
ABOVE
WELDABLE BARS EQUALLY-SPACED
EACH SIDE OF W-SECTION WEB,
WELDED TO ANCHOR PLATE
WELDABLE BARS 3 EQUALLY-SPACED
EACH SIDE OF W-SECTION WEB,
WELDED TO ANCHOR PLATE
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Past and Present
Are Tied Together:
Dominion Bank Building
The existing Dominion Bank building was originally con-
structed in 1914 to act as the bank headquarters. At the time
of its construction it was one of the tallest buildings in Canada.
The renovation would turn the office levels into additional
residential suites, add a dining hall, and add private meeting
rooms where the original main bank hall was located.
The original bank vault was retained in the basement of the
building and restored as part of a private club called the Dominion
Club. The vault now may be reserved for private meetings or
meals where business may be conducted in an intimate setting
that is “protected” from all manner of distractions.
The existing Dominion Bank building was constructed of un-
reinforced stone masonry that was considered adequate during
its age, but no longer meets code performance requirements.
Furthermore, it was crucial to provide compatible lateral sway
between the Dominion Bank Building and the new tower,
because of their intimate proximity to each other.
Engineers solved these inherent deficiencies and in-
compatibilities by simply allowing the existing Dominion
Bank building to be tied laterally or “lean on” the new tower.
One King West Tower is only 23 feet wide at its base. This narrow gap
makes the 610 foot tall One King West Tower one of the most slender
high rises in the world.
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STRUCTURE magazine June 2008
37
Thank you for reviewing this ad proof for the upcoming issue of STRUCTURE
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Magazine.
To ensure that the proper advertisement for your company is run, please print out this
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Inside_Cover_Outside_Cover_Perfe1 1 5/2/2008 2:24:35 PM
ADVERTISEMENT - For Advertiser Information, visit www.STRUCTUREmag.org
The Dominion Building bank vault. Currently the vault is being used as a private dining room
for special occasions.
Agha Hasan, P.Eng is a Principal with
Halcrow Yolles in Toronto, Ontario. He has
over 30 years of experience with analysis and
design of tall buildings with special emphasis on
wind and seismic effects. He may be reached at
[email protected].
The connection included a vertical slot so that
additional gravity loads were not collected by the
Bank Building, and prevented vertical shrinkage
incompatibilities with the tower. By using the tower
lateral system in this manner, no additional money
was necessary to upgrade or modify the existing
building’s lateral system. The architect was able to
spend this money on preserving and re-creating the
grandeur of the existing Dominion Bank interior.
Summary
By taking the simple concrete shear wall and
adding innovative features such as; rock anchor
foundations, outrigger columns, sophisticated wall
stiffness analysis, precision wind-tunnel studies,
and using tuned liquid dampers to reduce accelera-
tions, One King West Tower is an example of how
the past can be improved with the right touch of
modern ingenuity.▪
The author would like to acknowledge the contributions of Andy Bergmann, Peter
DiLullo, Chris Jacques, and Eva Ferenczi to the success of this project, and Terry
McDonnell who assisted in the writing and preparation of this article.
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