By Catherine A. Cardno, Ph.D.
As part of the 400 m long Glacier Skywalk in Jasper National Park, Canada, a 50 m wide glass-and-steel walkway extends from a cliffside, offering views of the Columbia Icefield.
The 400 m long Glacier Skywalk, located in Jasper National Park, Canada, opened this month. The path culminates in a 30 m long glass walkway that cantilevers from a cliffside, offering views of the Sunwapta Valley and Columbia Icefield. Brewster Travel Canada
May 20, 2014—The 230 km long Icefields Parkway in Canada, also known as Highway 93 North, parallels the Continental Divide—the region from which watersheds in North America separate to flow to the Pacific, Atlantic, and Arctic oceans. The parkway offers travelers unparalleled views of natural beauty as it spans the Rocky Mountains from Lake Louise in Banff National Park to the town of Jasper in Jasper National Park, extending through the Canadian Rocky Mountain Parks World Heritage Site, as designated by the United Nations Educational, Scientific and Cultural Organization (UNESCO).
With the opening of the Glacier Skywalk this month, visitors who travel along the Icefields Parkway now have the opportunity to traverse a cliff's edge and venture out onto a glass walkway that cantilevers 30 m in length over the Sunwapta Valley in Jasper National Park, providing views of the Andromeda and AA glaciers in the Columbia Icefield, as they slowly melt and move down the valley.
The 400 m long Glacier Skywalk path offers visitors the option of moving along a circuit built into the side of the cliff, as they travel past interpretive stations covering the biology, ecology, and glaciology of the region. The path is universally accessible and barrier free so all visitors—regardless of their mobility level—can enjoy the views. An amphitheater located near the cantilevered portion of the path provides a location for people to sit and enjoy the view, even without venturing onto the glass portion of the pathway.
The interpretive stations—one cantilevered, one in a cave, and one in a tunnel—are located along the pathway, which culminates in the glass skywalk, 280 m above the valley floor, according to the website of Canadian consulting engineers, Read Jones Christoffersen (RJC), the design lead and structural engineers for the project.
The glass walk is a self‐anchored eccentric suspension structure, while the solid part of the cantilever is composed of two trapezoidal steel box girders anchored to the mountain with a series of high-strength steel tendons. Robert Lemermeyer Photography for Sturgess Architecture
Calgary, Canada-based Sturgess Architecture was the architect of the project, which was a design/build effort spearheaded by the Calgary office of Edmonton, Canada-based PCL Construction. The $21-million effort-including planning, design, construction, and environmental assessment and monitoring-was undertaken and funded by Banff-based Brewster Travel Canada.
"Many visitors drive the breathtaking Icefields Parkway without ever actually leaving a paved roadway," said Mark Hendrikse, the director of marketing at Brewster Travel Canada, who wrote in response to questions posed by
online. "Along with our partners at Parks Canada, we wanted to encourage visitors to the area to stop, get out of their cars, and really connect with their surroundings."
At the same time, the Glacier Skywalk is unobtrusive to those traveling past the site, so that it does not compromise views. "The success of our piece is [that] you really don't see it until you get there, and so I think while its very heroic, it's also very graceful and very elegant, and indeed, subtle," says Jeremy Sturgess, a principal of Sturgess Architecture.
The glass portion of the walk is designed in a horseshoe shape that cantilevers from the side of the cliff, using the mountainside as the counter beam, according to Sturgess. He credits Simon Brown, Ph.D., P.Eng, a principal of RJC and the structural design expert for the project, for the concept, which Sturgess says "is brilliant in my mind." The walkway and the mountainside "work in harmony and create this cantilevered structure that [is] absolutely self-supporting," Sturgess says.
"We came along as the architect, and we bent that horseshoe so that it became not a parallel horseshoe, but an obtuse horseshoe—one that was sort of lopsided so that it focused …attention more on the view," Sturgess says. "And we were able to do that without compromising the structural integrity of the horseshoe."
Wind deflectors located atop the outer glass guardrail mitigate wind vibrations on the cantilevered structure. Four tuned-mass dampers are located underneath the outer glass rail, below floor level, to temper some—but not all—of the pedestrian-induced vibrations. Brewster Travel Canada
Steel was selected "to minimize the visual impact of the structure, as we did not wish to compromise the natural beauty of the site," said Brown, who wrote in response to questions posed by
online. "We want visitors to feel as though they are suspended in air," he said.
"The glass walk is a self‐anchored, eccentric suspension structure," Brown explained. The solid part of the cantilever is composed of two trapezoidal steel box girders created from custom-formed metal plates that are welded together and anchored to the mountain with a series of high-strength steel tendons that vary in length from 10 to 20 m.
"A draped suspension cable runs along the outside face of the inner guard rail," Brown said. "To counter the eccentricity of this support, the walk is curved in plan to generate a horizontal couple that cancels out the vertical couple." This system minimizes the amount of structure that is visible to visitors, particularly beneath the glass floor of the skywalk, according to Brown.
Steel tubes that were custom-bent in three dimensions support the glass portion of the walkway. The tubes contain cables similar to those used in large cable-stayed bridges, according to Brown. "Snow, wind, and pedestrian vibration loading were the prime considerations, largely due to the inherent flexibility of the structural system selected," Brown explained. "The snow load used for design is twice what was used for pedestrian loading, [and] vibration due to both wind and pedestrian action were both identified as potential challenges for this structure."
Wind vibration is mitigated by wind deflectors located atop the outer glass guardrail, and four tuned-mass dampers are located beneath the outer glass rail, below floor level, to temper pedestrian-induced vibrations, according to Brown. However, the design team wanted visitors to experience the skywalk at a visceral level, Sturgess says. So the dampers temper, but do not eliminate, "the wobble effect that you get when large numbers of people are walking on the skywalk," he says. "We deliberately want people to feel a little bit of
, or a
of scariness," Sturgess says. "That's deliberate."
Designing for dynamic and unbalanced loading was the biggest structural design challenge, according to Brown. "The issue with unbalanced loading, when you have people on only a portion of the glass walk, is that the system is designed and optimized for uniform loading," he said. "Under uniform loading, all of the main structural members act primarily as axial members, with little bending or torsional forces. Under unbalanced loading, bending and torsional forces become much more dominant [and] this results in increased flexibility and deflection."
To resolve these issues, the design team had to carefully design details for all of the possible unbalanced loading scenarios. "In particular, we had to be certain that the glass floor panels could undergo the deflection associated with unbalanced live loads," Brown said. "The end design utilizes the high torsional stiffness of the primary, hollow, structural-section compression member along with contributions [from] a number of secondary framing elements."
The glass system used in the walkway includes four layers. The bottom three layers are structural glass that has been tempered and heat-strengthened. These are topped with a fourth layer of sacrificial glass panels that create the surface on which visitors walk. "[The top sheet] is a surface treatment, and if it does get scratched over time, or if a piece breaks, then the top surface is easily changeable," Sturgess says. The design team wanted a system that would enable visitors to wear their own footwear—something that is not possible at the Grand Canyon's observation walkway, Sturgess notes. (See "Glass and Steel Skywalk Cantilevers from Grand Canyon Cliff,"
magazine, June 2007.)
The materials for the skywalk were chosen to blend into the cliff side. "While there was never any pretention that it should be anything but something that was man-made, it should be—within that context—as subtle and as sensitive a fit as possible to the mountainside," Sturgess says. To meet that goal, a minimal number of materials, and materials that would wear well without the need for protective coatings, were chosen. These included weathering steel that can be left exposed to the elements without deteriorating, glass, and wood in locations at which visitors will pause to enjoy the view or rest.
Although the Glacier Skywalk was made almost entirely of prefabricated pieces, construction took more than two years due to a brief, seasonal construction window—from the end of April to the end of October. The window was established to minimize the impact of construction on local wildlife in the spring and to account for the early arrival of winter in the region.
Visitors to the skywalk can access it by shuttles that depart from the nearby Columbia Icefield Glacier Discovery Center, located five minutes from the site.