In 2007, the need for an additional crossing over the Bow River presented Calgary, Alberta, Canada, with both an opportunity and a dilemma. Existing routes into the city for the more than 13,000 daily commuters—both pedestrians and cyclists—used three bridges. With an expected doubling of the city’s population in the next 20 years, the need for another bridge seemed an appropriate solution to ease congestion for the anticipated traffic. However, the problem with building a new footbridge lay with city restrictions that only allowed for a 23-foot vertical building envelope, thanks to a helicopter flight zone above the proposed site, the flood level of the river, and ecological concerns that prohibited mid-span supports in the water. The opportunity, then, lay in finding an architect to design a structure given these parameters, and the city chose Santiago Calatrava for the task.
Six years later, the new Peace Bridge is now open and each day brings more than 6,000 commuters into Calgary at a connection point just west of Prince’s Island. In a departure from Calatrava’s usual palette of white suspension apparatus, the Peace Bridge is a low, red cylinder slung between the two river banks it joins. A minimally profiled structural tube (approximately 19 feet high by 26 feet wide) was the design solution for Calatrava, who worked alongside structural consultant Stantec to develop a helical bridge that would perform without the claustrophobic side effects of a tunnel for its users. Bent structural glass between the curved steel frames forms the roof canopy over an open-air bridge deck, supported by diagrid steel decking, with lightweight cement as the surface. Originally, city planners had estimated about 4,000 daily users for the bridge. A recent study, however, found the numbers to be 50 percent higher than anticipated, with 1,600 users between the hours of 6:00 p.m. and 9:45 p.m., and 700 users after the commuter rush, from 8:00 p.m. to 9:45 p.m.
Lighting the bridge meant finding a way to integrate fixtures into an already minimal structural frame. Illuminated pathways at the deck level provide wayfinding for cyclists and pedestrians, respectively, while custom-length cathode light strips with opaque acrylic sleeves above form continuous lines of light. “The challenge was mostly from [Calatrava’s] office, in that they had this unusual length the lighting had to span, so we made custom fixtures,” says Steve Grossman, president of Cathode Lighting Systems, the Maryland-based company that fabricated the 14-foot luminaires. “There is steplighting below, but this was more of a decorative line of light, not driven by footcandle requirements, with segments of that lighting that go from one structural beam to the other.”
The decision to use linear fluorescents, Grossman recalls, was based on the flexibility of those sources and how they can be customized to any specification; in their Peace Bridge application, each unit contains three 4-foot 4000K linear fluorescent fixtures, with the appeal being their consistent color rendering and reliable technology. Inset within tubes, these fluorescent fixtures reinforce the bridge’s structural complexity, complementing the bridge’s form with their own and keeping the Peace Bridge aglow at all hours.
Details
Project: Peace Bridge, Calgary, Alberta, Canada • Client: City of Calgary • Architect: Santiago Calatrava Architects and Engineers, New York • Engineer: Stantec, Calgary, Alberta, Canada • Glazing Consultant: GIG Fassaden, Austria • Project Size: 10,840 square feet (150 square meters) • Manufacturers/Applications: Bega (26W compact fluorescent IP65-rated floodlight at bottom bridge cord); Cathode Lighting Systems (14-foot custom-length cathode light strips); The Light Edge (4100K T5HO linear fluorescents recessed at base of pedestrian balustrade); Senso Light (inground LED uplights at pedestrian walkway curb)
More details on the Peace Bridge appear in the story "Making Peace," written by Wanda Lau, which highlights the Peace Bridge's structural properties, and was featured in the May 2012 issue of ARCHITECT Magazine.
