sf onekingwesttower june08

8/13/2019 SF OneKingWestTower June08

1/4STRUCTURE magazine June 200834

of view within this extremely narrow projectsite in the middle of an urban nancialdistrict. The overriding concern during

design for all these technical design issues was the buildings 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 innovationsthat were implemented in selected locations.The rst innovation was to use outriggerconcrete walls at the lower levels (Floors 14though 16) supported on jumbo outriggerstructural steel columns. These steel columns

were subsequently embedded with surgicalprecision through a portion of the existing

Dominion Bank building. This maximizedthe width of the building at its base to justover 46 feet, reducing the overall buildingslenderness to just over 13:1, still large, butmore economical. While this expansion ofthe overall lateral force resisting system base

width was helpful, tremendous uplift forcesremained and needed to be resisted withinthe building foundations.To counter these large uplift forces, the

main foundation for the tower consisted ofa 3-foot thick concrete strip footing grid-

work that included over 100 rock socketed

BackgroundOne 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 theDominion Bank building, an architectural stalwart of thecity built in 1914. Because this historic structure was to formpart of the new tower, and because the remaining open site

was limited to just over 26 feet wide, the location demandedinnovative solutions and approaches throughout the designand construction process. This extremely thin piece of landhad to support a tower program that included over 500,000square feet of supported oor area, 570 luxury residentialsuites, and 100 parking spaces. Stanford Downey Architects

was charged with not only making this space elegant andinspiring, but also to have a profound impact on the Torontoskyline. The property owners goal was to attract high proleclients with a taste for grandeur. Working closely with theHalcrow Yolles structural engineers, and after many monthsof design coordination, an innovative structural system wasdevised that enabled a new, slender tower to merge with theexisting Dominion Bank Building.

Inspired Innovation: The Slender Tower

The result of many design meetings was a 610-foot (measuredfrom foundation to rooftop) high residential concrete towerthat is sandwiched between the Old Dominion Bank buildingand the adjacent property. To accomplish this height, the towerslenderness ratio (total height divided by width) would needto be around 23 at its narrowest width. This slenderness ratiois arguably one of the worlds largest for a high-rise building atthe time construction began.The biggest challenge for the structural engineers was

to design a lateral resisting system that would meet thisslenderness ratio and satisfy the base overturning forces, driftdue to wind loads, comfort acceleration criteria, and also keepthe building economically feasible from a construction point

I NSPI R I N

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I NNO

VATI ON

On K ng We T w r

The task of successfully merging historical grand dcor with sleek modernism is achallenging one. One King West Tower in Toronto, which marries the historic to the

progressive through technical innovation and functional inspiration on a grand scale, isan example of how that challenge can be met to create a striking landmark structure. OneKing West Tower merges the turn of last centurys stone masonry Dominion Bank Buildingwith 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 condominiumin the central business district of Toronto, Ontario, Canada. The toweconstructed integrally with the Dominion Bank building in the foregrCourtesy ofDrew Hauser.

The nite element mode for One King West Towunder gravity and windsway deformation. Thecolor changes denotedifferent concrete streng



Construction of the liquid tuned dampers atthe top of One King West Tower.

anchors drilled to a depth more than 30 feet into rock. More than 50% of theseanchors (including all of the anchors installed within the existing DominionBank building) were pre-stressed into place in order to activate them to resist uplifteven during construction.Next, engineers performed a rigorous nite element model of the tower concrete

shear wall lateral system. Historically, tall buildings exhibit cross wind effectsthat magnify the short direction dynamic properties and wind sway of a building.However, for buildings with large planar aspect ratio, the cross-wind vortex sheddingalong building length is poorly correlated due to wind ow reattachment. This wasconrmed in wind-tunnel analysis which concluded that the along-wind buffetinggoverns 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 inconcrete shear walls under the combined effect of wind and gravity loads. Usingthese relationships, the engineers on One King West Tower diligently calculatedstiffness loss at every level and applied these values when analyzing the buildingunder gravity loads, lateral loads, and dynamic effects. Because gravity loadsway played a major role in building lateral displacement, different wall crackingparameters had to be adopted for easterly and westerly winds. This resulted increation of two independent models for wind and gravity load analysis for easterlyand westerly wind cases.

One King West Tower under construction.

High-rise buildings must also be evaluatedfor occupancy comfort when undergoing

wind induced oscillations. This is done by rstmodeling the dynamic properties within a niteelement program, then verifying these dynamicproperties with wind tunnel testing. One simplemethod of determining occupancy comfortis to measure the acceleration at the top oorsof the building under the worst wind induceddynamic condition. Usually an accelerationvalue under 15 milli-g is considered acceptablefor residential buildings. For One King StreetTower, along its narrow East-West dimension,the accelerations were originally reported tobe as high as 17 milli-g by the wind tunnel.In order to reduce the accelerations economi-cally, Halcrow Yolles along with BoundaryLayer Wind Tunnel Laboratory (BLWTL) im-plemented a tuned liquid damper that wasinstalled at the top of the tower. This damperused water lled tanks to a specic height

within roof-top concrete tanks to counter the wind induced dynamic effects. The tunedliquid tuned damper (TLD) may be tuned tothe individual building frequency of concern byadjusting the height of the water in the tanks.For buildings in this acceleration range, for

which wind resonant effects are substantial, theimplementation of dampers may lead to overall

wind force reduction, and correspondingsavings in material building costs. Furtherevaluation of tuned liquid tuned dampers arebeing monitored under a long-term plan aidedby a Canadian government grant.

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The shear wall outrigger connection detail.This detail shows how Halcrow Yollesengineers connected the interior concretecore walls to the exterior steel columnsthat were surgically placed within the OldDominion Bank Building.

W460x82 C LSTEEL COLS BELOW

WELDABLE BARSWELDED TOW-SECTION FLANGE

SHEAR STUDS

10

WELDABLE BARS WELDEDTO ANCHOR PLATE

ANCHOR PLATE

PLATE EACH SIDE OF W-SECTION WEB WIDTH TO MATCHW-SECTION FLANGE

45 CONT

STIFFNER PLATE WELDED ALL AROUND TO COL SECTION EACH SIDE

STEEL COLUMN

ANCHOR PLATE

12

DEFORMED ANCHOR BARSWELDED TO W-SECTION FLANGES

SHEAR STUDS AT MID-DEPTH EACH SIDE OF W-SECTION WEB

FIN FLOORLEVEL

ELEVATION

WELDABLE BARS EQUALLY-SPACEDEACH SIDE OF W-SECTION WEB,WELDED TO ANCHOR PLATE

WELDABLE BARS 3 EQUALLY-SPACEDEACH SIDE OF W-SECTION WEB,WELDED TO ANCHOR PLATE

W - S E C T I O N F L A N G E S C U T

PLAN

CONC WALL ABOVE SHEAR-STUDS

WELDABLE BARS

C L CONC WALL ABOVE

Past and PresentAre Tied Together:

Dominion Bank BuildingThe existing Dominion Bank building was originally con-

structed in 1914 to act as the bank headquarters. At the timeof its construction it was one of the tallest buildings in Canada.The renovation would turn the ofce levels into additionalresidential suites, add a dining hall, and add private meetingrooms 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 DominionClub. The vault now may be reserved for private meetings ormeals where business may be conducted in an intimate settingthat is protected from all manner of distractions.The existing Dominion Bank building was constructed of un-

reinforced stone masonry that was considered adequate duringits age, but no longer meets code performance requirements.Furthermore, it was crucial to provide compatible lateral swaybetween the Dominion Bank Building and the new tower,because of their intimate proximity to each other.Engineers solved these inherent deciencies and in-

compatibilities by simply allowing the existing DominionBank 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 gmakes the 610 foot tall One King West Tower one of the most slendhigh rises in the world.



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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 withHalcrow Yolles in Toronto, Ontario. He hasover 30 years of experience with analysis anddesign of tall buildings with special emphasis onwind and seismic effects. He may be reached at

[email protected].

The connection included a vertical slot so thatadditional gravity loads were not collected by theBank Building, and prevented vertical shrinkageincompatibilities with the tower. By using the towerlateral system in this manner, no additional money

was necessary to upgrade or modify the existingbuildings lateral system. The architect was able tospend this money on preserving and re-creating thegrandeur of the existing Dominion Bank interior.

SummaryBy taking the simple concrete shear wall and

adding innovative features such as; rock anchorfoundations, outrigger columns, sophisticated wallstiffness analysis, precision wind-tunnel studies,and using tuned liquid dampers to reduce accelera-tions, One King West Tower is an example of howthe past can be improved with the right touch ofmodern ingenuity.

The author would like to acknowledge the contributions of Andy Bergmann, PetDiLullo, Chris Jacques, and Eva Ferenczi to the success of this project, and TeMcDonnell who assisted in the writing and preparation of this article.

sf onekingwesttower june08

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