The design of a 49-story angled tower to be located in Vancouver, British Columbia, is currently under way. The tower has a mere 557 m² triangular footprint at ground level, but it expands once it clears the space above a nearby bridge to become a square building with 1,160 m² floor plates. BIG & Luxigon
The triangular floor plate at the ground level of a new, top-heavy tower in Vancouver, British Columbia, will give way to square plates as the structure rises.
March 19, 2013—An appealing 49-story, angled tower design created by Bjarke Ingels Group (BIG)—of Copenhagen (København), Denmark, and New York City—and the Vancouver, British Columbia, office of DIALOG has been unveiled for the Vancouver, British Columbia, skyline. Limited to a triangular footprint occupying a mere 557 m², the tower expands once it clears the space above a nearby bridge to become square, its floor plates encompassing 1,160 m². A series of mixed-use, triangular podiums cluster around the base of the tower, creating opportunities for interaction with passersby through 60,600 m² of residential, retail, and commercial space.
The unusual top-heavy massing and upward sloping geometry of the tower created a “daunting challenge, especially in the high seismic zone of Vancouver,” says Erleen Hatfield, P.E., AIA, LEED AP, M.ASCE, a principal in Buro Happold’s New York office and the firm’s partner in charge of the structural design concept for the tower. The gravity loads alone would be enough to overturn the building, she explains.
“Although it seems unusual when you look at it, there really is a method to their madness,” says Hatfield. “Maximizing those upper floor plates—the high-value square footage up there [and] the views of the park and the river—was really a very ingenious approach.”
The tower will be constructed of concrete, according to Hatfield, and posttensioning will be used in the reinforced core and shear walls to increase strength. “Concrete was chosen primarily based on the client’s desire to maximize clear floor heights and also to easily achieve the residential fire ratings,” she says. Two-way flat plate floor framing will be used for each story.
The posttensioned core will act as a spine to keep the tower upright, while lightweight concrete will be used in the floor plates to help reduce the overturning tendency from the gravity loads, according to Hatfield. “The core resists the wind and seismic loads,” she says, pointing out that since “the seismic loads are quite high in Vancouver, the core is a very, very important piece in this structure.”
The tower is part of a 60,600 m² mixed-use complex that will be
located along Beach and Howe streets in Vancouver. A series of
mixed-use triangular podiums will cluster around the base of the
tower and be tucked in between the Granville Street Bridge and
its on- and off-ramps. BIG & Luxigon
The shear walls will impart lateral stability, anchoring the building against the “leaning” force created by the upper floors, according to Hatfield. Moreover, “as the tower floor plates grow, the concrete columns walk, or step, to follow the sloped southeastern facade,” she says.
“This design will result in an efficient structure that is also economical to build,” says Hatfield. “Because even with the unusual geometry, it is still a developer-driven tower” that must meet the client’s requirements. Fortunately, the developer, Westbank Corporation, “are forward thinkers,” Hatfield says.
The design team is currently wrapping up the schematic design of the complex, and Rob Simpson, P.Eng., LEED AP, a principal of Glotman Simpson Consulting Engineers, a structural engineering firm based in Vancouver, British Columbia, will take over as the local engineer of record.
The complex will be located along Beach and Howe streets within the city and will be tucked between the Granville Street Bridge and its on- and off-ramps. It is a tricky site in that the bridge ramps trisect the site, and the elevation changes by 9 m from one side of the site to the other, according to Thomas Christoffersen, the partner in charge of the project for BIG and the design director of the firm’s New York office. Christoffersen says that the tower had to include several setbacks at its base to accommodate possible street expansions, limit the shadows on a nearby park, and provide 30 m of clearance from the bridge for safety reasons.
“The bridge and the on-ramps are something that we have been very much aware [of]—how do we bring daylight down there, how do we make it an attractive and active environment in the evenings, and so on,” Christoffersen explains. The mixed-use, glass-enclosed podiums are meant to answer those questions, as is a ramp that will enable pedestrians and bicyclists to descend from the bridge to the podium site for shopping or dining.
The triangular podium buildings will enable interaction with people
at the street level. The design team had to work within the
constraints created by the bridge ramps that trisect the site, as
well as a 9 m elevation change from one side of the site to the
other. BIG & Luxigon
The triangular podium buildings will feature fairly straightforward, typical construction with glass facades, according to Christoffersen, although the arrangement of the space will be crucial because the buildings will face the spaces beneath the bridge and ramps. “We have to think of the urban space in a different way than you typically do in that area of Vancouver,” he says.
The small triangular podium buildings will be nestled together to create private, interior courtyards. The rooflines of the podium components will be sharply sloped, the current design calling for green roofs that will be visible above the line of the bridge and its ramps. “The sloped roofs are there to give a special experience when you arrive to Vancouver on the bridge and when you leave,” says Christoffersen, who explains that the slope “exposes the green roofs as landscape elements, almost as if you were driving at grade. . . . On one side you would see a hill or a mountain of green, and on the other side you would see a piece of the facade of the opposing building that peeks up between the bridge and the ramps.”
The rainwater absorbed by the sloped, green roofs, Christoffersen notes, can be reused on-site as gray water. This will also prevent the city’s sewer system from being overwhelmed during heavy rainstorms.
World Architecture News singled out the tower for an award in the residential category last year, and the award was presented last month.