Engineering
Glacier Discovery Walk
Sturgess Architecture
The stunning glass and steel walkway will give visitors an experience to remember. By Simon Brown
T
he Glacier Discovery Walk, now under construction in Jasper National Park, is destined to become one of the most exciting and unique attractions in the Canadian Rockies. Owned and operated by Brewster Travel Canada, this privately funded project leverages heart-stopping visitor experiences to create an emotional connection to the importance of environmental stewardship. The project has been designed for minimal environmental impact and is constructed entirely on the previously disturbed land of an existing road cut. Guests first proceed down 300m of wheelchair accessible trail cut into the side of a cliff high over the Sunwapta Valley. As they proceed down the trail, interpretive stations provide information on the geological and glacial forces that created the valley, the plants and animals that inhabit it, as well as the role of water flow and climate change on its future evolution. At the end of the trail, visitors reach the climactic Discovery Vista. The design build team of PCL Construction Management, project lead, and Read Jones Christoffersen, design lead, have maximized the inherent drama and exposure of this area with a cantilevered viewing platform
30 construction business
July/August 2012
that extends over 30m from the face of the cliff. The platform features at its apex 30m of glass walkway suspended over 200m above the valley floor. The glass floor and railings of the walkway will give guests the impression of floating in air. The experience is intended to be both exciting and intense. The steel and glass walkway is supported with a self-anchored cable suspension system on one side only. The apparent eccentricity of this system is counterbalanced by horizontal forces created by curving the walkway in plan. The geometry of the walkway has been precisely determined to eliminate torsional stresses under uniform load. A large HSS compression chord, acting with secondary steel framing members, provides torsional resistance under partial loading conditions. This system was selected as it minimizes visible structure below the glass floor, thereby maximizing the sense of exposure. Tuned mass dampers will be utilized to mitigate vibration under dynamic loading. The glass walk is supported at the end of cantilevered trapezoidal steel box girders. These provide the very high strength to weight ratio required for the project. In addition, the closed
form of the box girders results in superior torsional stiffness. The girders are being fabricated in Eastern Canada by Beauce Atlas Steel, shipped via truck to site, and then lifted into place by crane. The larger of the two main girders has a mass of approximately 146,000kg and is 46.5m long. As a result, it needs to be shipped and hoisted in four separate pieces. Bolted splices have been used to speed erection and minimize the need for full penetration welding in the field. The largest of these connections contains 980 high strength bolts. The girders are secured to the cliff with 60 rock anchors that extend 10 to 20 metres into the native bedrock. When considering the most appropriate finish for the girders, three parameters dominated the discussion. These were corrosion protection, aesthetics, and maintenance requirements. A painted finish was rejected as it would be difficult to maintain over the lifespan of the structure. Hot dipped galvanizing was also considered. This addressed the long-term corrosion protection and maintenance concerns, but was less desirable from an aesthetic standpoint. We wanted a finish that would blend into the natural surroundings. The perfect solution was to specify weathering steel, which does not require any finish. Over time, exposure to air creates a layer of rust that adheres tightly to the surface of the steel. This oxide layer forms a natural protective coating that minimizes further corrosion and eliminates the need to maintain a separately applied finish. In addition, as the girders age, they take on a dark brown colour that compliments the iron oxide found in the surrounding geology of the area. The architectural style and overall feel of the project was created by Sturgess Architecture. Angular steel plates form faceted surfaces that play off the jagged nature of the surrounding cliffs and valleys. These are also fabricated of weathering steel, creating a unified expression with the steel girders. Glass elements have been selectively introduced into railing elements. These provide better viewing for younger visitors and those in wheelchairs. The glass elements also symbolize the glacial ice of the Columbia Ice Fields above. This treatment remains consistent not only at the Discovery Vista, but also at each of the interpretive stations and at the receiving area where guests are greeted. The Glacier Discovery Walk is under construction through the summer and fall of 2012 and spring of 2013. It will be ready to welcome guests from around the world in the summer of 2013. Simon Brown, Ph.D., P.Eng., is a principal at Read Jones Christoffersen Ltd. in Calgary and the lead designer on the Glacier Discovery Walk project.