Designing a glass-floored platform that thrusts visitors 115 feet from a mountain side and 918 feet above grade goes beyond the typical litany of challenges that an architect encounters on a project. Throw in a fear of heights and you’re in the position that Canadian architect Jeremy Sturgess has faced for the past three years.
With a portfolio filled with mostly residential projects, the Sturgess Architecture principal, in Calgary, Alberta, Canada, is more accustomed to designing on solid ground. But then the opportunity came to team with Read Jones Christoffersen Engineering (RJC) in a 2010 design/build competition to create a fully accessible visitor destination overlooking the Athabasca glacier about 120 miles north of Banff, Alberta.
“There was a preconception [that the structure would be] a high-masted, cable-stayed support system,” Sturgess says. But RJC principal and structural engineer Simon Brown had a different vision: a cantilevered, horseshoe-shaped, box-beam structure with no visual interruptions above the sight line. “We intuited that it would really appealing to Parks Canada if this [design] would ultimately be very sympathetic to the natural landscape,” Sturgess says. The design/build team of RJC, Sturgess, and general contractor PCL Construction won the project in January 2011.
Last Friday, May 16, the Glacier Skywalk and Discovery Center officially opened to the public. Designed in one year and constructed in two summers—the short window between the mating season of the indigenous mountain goats and the onset of winter in mid-October—the approximately 1,500-foot-long walkway traces the mountain edge before culminating in the 98-foot-long cantilevered horseshoe with the glass floor.
Beyond the views, visitors gain an education on glacier formation, geology, life sciences, and the engineering and design of the project via interpretive stations along the walkway. Edged by a series of folded metal plates, the walkway also contains several pausing points, including a six- to eight-person cantilevered “basket that gives you a precursor” to the cantilevered precipice, Sturgess says. “Your whole journey is being compressed … just prior to expanding onto the walkway itself.”
The origami of steel plates was “a whole new discipline” for Sturgess and his team in terms of the level of detailing, connections, and project coordination. The firm worked with Calgary fabricator Heavy Industries to 3D model ways to fold Cor-Ten steel in an economical manner that also served as “a manmade expression of the natural state,” Sturgess says. “This was not meant to be a piece of jewelry. … The edges can be a little rough, but they're all designed.”
To Brown’s vision for the Discovery Skywalk’s cantilevered platform, Sturgess and his team imparted two key design suggestions. “We twisted the horseshoe to have one larger arm and one shallower arm to face the view to the glacier,” Sturgess says. Secondly, they minimized the specified materials to namely Cor-Ten steel, wood, and glass. The paint- and toxin-free materials will weather naturally with the landscape. “The glass of the hand rail, as it gets extruded out of the jaws of the Cor-Ten beams, is evocative of the lichen … that comes out of the mountain side,” Sturgess says.
Like many projects, one challenge was staying within the budget, which the Edmonton Journal reported as $21 million. Sturgess half-jokes that because he was nervous about walking on a glass floor, he suggested switching to a steel-mesh floor to save costs. But Brown and PCL construction manager Scott Updegrave, a mountain climber, insisted on glass. “It was important to Simon that you not walk around [the horseshoe] casually,” Sturgess says.
The jarring realization that just four plies of glass, totaling 1.6 inches in thickness, separate you from freefalling is one reason that visitors inching along the horseshoe may set their jaws. RJC also designed the relatively lightweight structure to flex and vibrate with pedestrian movement, Brown says. However, four tuned-mass dampers, designed to vibrate at the same frequency of the structure, keep the platform from the extreme resonance that plagued London’s Millennium Bridge when it first opened.
Structurally, the slightly banked Skywalk is supported by suspension cables on the inside curve and steel box girders below, Brown says. It supports twice the snow design load of approximately 4,200 pounds per square foot, and four times the live design load of 2,100 pounds per square foot. Each of the two 5-inch-diameter suspension cable bundles contains nine high-strength tendons, totaling about 1,640 feet in length, and resists about 380,000 pounds in tension.
The two steel box girders under the glass platform connect to high-tensioned steel rods that anchor 66 feet deep into the mountain’s composition of interbedded limestone and dolomite rock.
Beyond gravity loads is the matter of wind. In the open Sunwapta Valley, the one in 100-year-wind speed is about 89 miles per hour, Brown says. As such, the inclined glass plates mounted above the curved-glass handrail of the platform are more than climbing deterrents. Rather, they act as deflectors to “break up the wind pattern so you don’t get that successive increase in amplitude,” he says. RWDI Consulting Engineers, based in Guelph, Ontario, Canada, helped design and test the wind deflectors.
The project was commissioned by Brewster Travel Canada (BTC), which responded to the Parks Canada’s desire for private sector initiatives to encourage visitors to experience the landscape outside of their cars in a novel way with minimal impact on the environment.
To address any concerns that the Glacier Skywalk construction would harm the natural landscape and ecosystem that they sought to celebrate, BTC commissioned a third-party environmental assessment of the project’s impact on wildlife and vegetation. The study’s findings were deemed acceptable by Parks Canada’s natural resources management standards and will become a reference point for three years following the walkway’s opening. The project team also took care to limit the walkway’s footprint to previously disturbed land that was zoned for recreational purposes.
