Award of Excellence Glacier Skywalk
October 1, 2014
By Read Jones Christoffersen
Located in Jasper National Park, Alberta, the Glacier Skywalk is a thrilling and dramatic structure featuring a 30-m curved glass walkway that extends 35 metres from a cliff face and 280 metres above the Sunwapta Valley. One doesn’t have...
Located in Jasper National Park, Alberta, the Glacier Skywalk is a thrilling and dramatic structure featuring a 30-m curved glass walkway that extends 35 metres from a cliff face and 280 metres above the Sunwapta Valley. One doesn’t have to be an engineer to appreciate the technical complexities of this project. Even before it was built, the Skywalk gained international attention with a World Architecture Award.
The owner, Brewster Travel Canada, wanted to create a world class experience for visitors. Given the sensitive location, it was also very important to Brewster that the project would not detract from the natural beauty of the area.
Read Jones Christoffersen was the design lead and structural engineer, with PCL Construction as project lead, doing construction and quality management, and Sturgess Architecture.
The exhilarating perspective offered by the steep cliff face and the narrow valley provides spectacular views of the waterfalls from a very high angle.
The team wanted to push the limits of the sense of exposure and decided that the best approach was a glass floor, minimizing the appearance of the structural support.
To maximize the “wow” factor it was decided not to use a high-tech cable-stayed system. There should be nothing above the viewing area to compete with the grandeur of the natural scenery or interfere with people’s views. Cantilevering the structure offered two advantages: not having to perform work down the face of the cliff and minimizing the amount of visible structure.
Support on inner edge only
A self-anchored cable suspension system was used for the glass walk. By taking advantage of the walkway’s curved plan the engineers were able to support the structure on the inner edge only. Because the bridge is curved in plan, the suspension cable not only pulls up on the walk, it also pulls horizontally inwards.
By varying the degree of the walk’s curvature, the engineers were able to change the amount of horizontal force and determine the precise shape to optimally counterbalance the effects of the single sided support. Not only did this system minimize visible structure below the glass floor, it also kept the outer glass rail free of structure. The result is a highly efficient and non-intrusive structural system.
Dampers and wind deflectors
Although the system is highly efficient in carrying load, it is also relatively flexible. Four tuned mass dampers mitigate vibration due to pedestrian loads. The dampers are located under the outer edge of the Skywalk and are visible through the glass. Early in the design wind consultant RWDI also identified the need to modify the geometry of the walk to mitigate excessive vibrations under wind loading. Wind tunnel testing explored different wind deflector geometries to find the least intrusive shape that would still be effective. The detectors specified are glass elements mounted to the top of the outer rail, disguised as feature elements of the walkway.
The complexity of the structure is primarily due to its challenging dynamic behaviour, which required 3-dimensional finite elemental models and non-linear time history studies. The predictions were confirmed by monitoring the behaviour of the completed structure on site. Vertical accelerations due to pedestrian activity have been restricted to 5 per cent of gravity. Some movement can still be felt, but this is considered to be a positive feature of the design (“We don’t want people feeling too comfortable!”)
During the rock excavation for the foundations of the 45-m cantilevered girder a large fracture was uncovered in the rock directly below the greatest reaction load. Immediate redesign work was required to develop a foundation system that would safely carry the loads past the fractured rock and into the solid rock below. This was achieved by using 14-m long mini-piles. The fractured rock was then stabilized with additional horizontal rock anchors installed below the main footing in the cliff face. This redesign was fast tracked to ensure that the new piles and anchors could be installed before the end of the construction season. Otherwise the installation of the girders the next season would have been delayed, with an associated ripple effect.
Since the Skywalk opened this year, visitors from around the world have come to experience the thrill of walking on glass high above the Sunwapta Valley in one of Canada’s most stunning National Parks. cce
Project name: Glacier Skywalk,
Jasper National Park, Alberta
Award-winning firm (design lead &
structural engineer): Read Jones
Christoffersen, Calgary (Dr. Simon Brown, P.Eng., Geoff Kallweit, P.Eng., Mark Ritchie, P.Eng.,
Stefan Franke, P.Eng.)
Owner: Brewster Travel Canada
Client: PCL Construction Management
Other key players: Sturgess Architecture (architect); SMP (electrical);
Urban Systems (civil); RWDI
(wind modelling); Thurber Engineering (geotechnical); Golder Associates
Supplier: Bova Steel