A Unique Bridge Design
Paris-based RFR SAS, in partnership with WSP was selected for the planning, design, and construction of the iconic George C. King Bridge in Calgary, Alberta (Canada).
The client’s main objective was to create a link to the East Village development and access to St. Patrick’s Island while improving cyclist and pedestrian paths in Calgary.
Innovating to Help Overcome Challenges
The project presented challenges and requirements that were addressed with originality and innovation.
The client recognized early on the risks posed by Bow River’s changing water flow, setting specific seismic, hydraulic, geotechnical, and geometric criteria. These robust criteria were put forth to make sure the bridge would resist a fast moving river and ice build-up of up to three meters thick.
St. Patrick’s Island being below the flood elevation chosen by the client, the bridge deck could not touch down on the ground. To palliate this issue, the team designed a secondary ramp linking the island span to the ground surface.
The most important and unexpected challenge occurred in June 2013 following unprecedented flooding in Calgary, that washed out critical deck false work. A post-flood investigation revealed significant damage to the bridge deck, setting back the project completion date by a year. However, it also proved that although incomplete at the time, the bridge resisted an exceptional situation.
Other construction challenges were related to the slender nature of the bridge, which called for careful attention to interfaces between the steel arches and the concrete deck. From sequencing of installation operations to hanger cable tensioning, the design further presented construction challenges in ensuring that the arches and deck worked as a network arch.
Elegance and Resilience
The design was able to harmoniously bridge two very distinct qualities of the site: a vibrant urban environment with a majestic natural setting. The intention was to make the George C. King Bridge a destination in itself to observe the Bow River beneath and contemplate the cityscape. The three-span 182-metre long bridge evokes stones skipping along the surface of water.
The team created a slender and unobtrusive arch design leading lightly across the river, to complement and follow the natural beauty of the surroundings. Slenderness of the arch is achieved in large part through two innovative design components:
Linking the arches together with the prestressed concrete deck tie across the spans and engaging the network of cables, arches and deck. The inclined intersecting hanger cables link the arch and deck creating a network arch, resulting in a very efficient structural form. Where a traditional approach would have been to build three separate arches in line, our unique design is able to resist concentrated loads, while each arch can be quite slender.
Creating a structural steel shape with a high degree of accuracy while meeting rigorous requirements for surface finish. The arch ribs are each composed of a pair of steel tubes offset and welded together via top and bottom plates to form a wide section with rounded sides. The horizontal offset increases the moment of inertia of the section to resist out-of- plane buckling while maintaining its elegance. In this case, the top and bottom plates are integral to the strength of the rib and not simply a cover plate to create an architectural shape.
Finally, the design includes lighting integrated in the balustrade to illuminate the deck without using visually disruptive light poles. The main lighting design concept was for the bridge to transition from day to night and night to day. During day light, the arches are the most fascinating aspect of the bridge. As sun goes down and the bridge lights go on, the gently lit deck of the bridge magnifies the flat and slender (suspended) structure while the arches take a step back and gradually disappear. Additional lighting integrated in the deck illuminates the land and water below the deck after dark, creating a soft bed of light influenced by seasonal changes to the landscape.
This award-winning project is an excellent example of an international team’s collaboration resulting in a unique and innovative footbridge. The team’s close attention to detail, while respecting all safety requirements, created a bridge that the population will want to visit and not only use to cross the Bow River. Details such as making the bridge support structure as transparent as possible along with a controllable LED system allowing for an interactive or programmable lighting scheme. All these specificities make the George C. King Bridge a success and brought full satisfaction to our client.