Fort Edmonton Bridge under construction. Photograph by Nordahl Flakstad.
The latest pedestrian and bicycle crossing over the North Saskatchewan River pushes Edmonton’s extensive multiple-use trail system westward. It also provides an unusual piece of Prairie scenery — a suspension bridge.
Apart from a 50-year-old crossing of the Peace River at Dunvegan, Alberta, and a few smaller variants hidden away in locales like golf courses, suspension bridges are rare in the Prairies.
Due for completion this fall, the new $23-million Fort Edmonton Footbridge, joins that limited list. CH2M HILL was the prime consultant on the project, which is located in the city’s West End. The bridge connects the Patricia Heights, Westridge and Oleskiw neighbourhood with existing bank trails and with Fort Edmonton, an outdoor museum housing replica and historic buildings dating back to fur-trade days.
For project manager Gary Kriviak, P.Eng. of CH2M HILL a suspension bridge was a natural choice. “A key objective of the client (the City of Edmonton) for the crossing was to have a well suited signature-quality structure that would be a destination, as well as a functional crossing.”
Though there is nearby housing, it’s mostly hidden by vegetation and curves in the river valley. The bridge shares some of the organic lines prevalent in the meandering waterway, and was selected to complement not clash with the natural surroundings. Besides pleasing the eye when viewed from afar, the bridge has gathering plazas integrated into its structure to provide those using the bridge with enhanced views of the natural surroundings. The so-called “belvederes” at the two towers and at each entrance to the bridge are offset from the main deck alignment and offer bucolic vistas of the river valley.
Construction began in 2008 on the 246-m long structure, which has a 138-m middle span. Some 30-40 m from each shoreline, in-stream piers/towers rise approximately 30 m from the streambed. Below the deck-level, 14-m high concrete pier shafts extend up from the channel supported on concrete caissons sunk about 12.5 m into the riverbed.
The above-deck portion consists of twin steel towers that support sculpted cast-in-place, reinforced concrete tower caps. The suspended bridge deck is formed from a series of 3-m long pre-cast concrete segments post-tensioned together, forming a 4.5-m clear pathway.
The suspension cables are anchored in cast-in-place reinforced concrete, hollow rectangular boxes secured to the foundation soils with ground anchors. While larger suspension bridges generally require spinning of cables on-site, this “smaller” footbridge employs a pair of continuous pre-manufactured cables imported from Europe.
The suspension bridge has been an interesting challenge for Kriviak and CH2M HILL’s design team. Since suspension bridges are rare in this region, and a relatively uncommon bridge form, the local building trades had somewhat limited experience with such construction. However, access to global design support and know-how made the task easier than it might otherwise have been. The project team included internationally recognized bridge designer Jiri Strasky; HFKS Architects (aesthetics); Boundary Layer Wind Tunnel Laboratory (wind and pedestrian dynamics); Thurber Engineering (geotechnical); NHC (hydrotechnical); EDA Collaborative (trail system); AMEC and CH2M HILL (environmental), and Alberco Construction as general contractor with Cohos Evamy as erection engineer.