Spooned into the banks of the Bow River is one of the iconic landmarks in the Calgary City of Canada. This icon named Peace Bridge is a pedestrian footbridge with a helix structure composed of two tangential radii that create a unique architectural space. With a span length of 126 meters, this footbridge connects the citizens of the Sunnyside community of the north and the Eau Claire community in the south of Calgary. Designed by the exemplary Spanish architect and structural engineer Santiago Calatrava, The Peace Bridge commenced its profound life in March 2012.
The Ascension of Peace Bridge
The City of Calgary faced a question that presented to itself both as a problem and an opportunity. By 2007, more than 13000 daily commuters (both pedestrians and cyclists) used three bridges to travel in and out of the city. From the survey conducted by The City Council, the city expected a doubling in their population in the next 20 years. Hence, a fourth bridge was necessary to reduce the foreseen passenger congestion without causing any downfall to the surrounding environment.
Moreover, there were several challenges to be solved concerning the proposed site. To name a few, the city regulation of restricting vertical building envelope to 7 meters because of the helicopter flight zone, ecological concerns that off-limited the usage of mid-span supports over the water, and the flood level of the Bow River. These were unconventional problems faced for designing a pedestrian bridge.
Above these, all of the solutions had to be found within the allocated budget of 25 million dollars. So to tackle these issues, The City Council decided unanimously to bring in Calatrava.
Calatrava’s Design Philosophy
Upon the first site visit by the Bow River, Calatrava was greatly inspired by his surroundings. The architect also noticed that the bicyclists, joggers, and other pedestrians were undeterred by the harsh winters and continued to use the nearby pathways and bridges. Therefore, he wanted to design an aesthetically pleasing bridge that complements both the summer and winter seasons and protects citizens from intense natural conditions.
The outcome of this is an uplifting and inspirational bridge that is as functional during the winter as it is during summer. And a color philosophy of red and white, resembling the Canadian Flag and complimenting the seasons of Calgary.
Engineering the Masterpiece
Since the use of piers to support the bridge is not favoured, the entire weight of the structure is distributed to the end abutments by unconventional means. Calatrava came forward with the idea of using a tubular structure as the outer shell, which further enhanced into a form of the welded steel frame of intertwined helix structure wrapped around an elliptical cylinder.
The helical rack acts as a truss web that transfers load between the truss chords and linear steel members along the bridge’s top and bottom. Transverse strength is provided by the two edge beams and bridge deck. The concrete patio cast in place on top of the steel deck is 110 millimetres thick. It gets enveloped in an 8-meter broad oval cross-section that consists of a central bicycle lane flanked by a pedestrian lane on either side. In addition, the form of the cylinder got modified to have a curvature based on several circular radii instead of an ellipse’s continuously changing curvature to simplify manufacturing.
An Outlook on Construction Methodology
The bridge’s construction is sub-divided into three phases due to the complexity of the structure. In the first phase, the construction crew set up a temporary system across the Bow River for the helical structure’s initial reinforcement and preparations for the foundation support of the ends of the footbridge. At the same time, Calatrava’s team sent detailed drawings to a steelwork fabrication company named Augescon in Spain. After fabrication, the steel parts are transported to a remote location in Calgary (10 miles north of the proposed site). Phase two consisted of assembling each component and welding the fabricated steel pieces to form parts of the double-helix footbridge.
Welding this unique structure was a first, and there were many failed attempts in the welding process before reaching the desired quality of the weld. Finally, the frame gets welded into three parts for ease of transfer to the site.
One of the strenuous steps is phase 3. First, the welded outer frames are transported to the site’s location and laid on the temporary support. Once the structure clears the entire span, the construction crew lifts the precast concrete abutments into place. Then, between the gaps of each tangential radius of the helix steel structure, glazed leaves panels get attached to the steel frame. Finally, the temporary structures get set aside. In this manner, Calatrava progressed to ensure people’s feeling of an open crystalline environment and reduce the harmful impacts on its surroundings.
Planning for the Present and the Future
Keeping the city’s priorities and environmental duties to be fulfilled in the back of the mind, Calatrava designed the Peace Bridge. The 126-meter long footbridge is a single-span structure without piers. It significantly reduces the environmental impact on the Bow River. Along with this, the footbridge has been designed to withstand Calgary’s one-in-100-year flood cycle and is constructed with high-grade materials to have a minimum life span of 75 years. Due to its single-flow design, it provides barrier-free access for people of all mobility types.
Calatrava’s design fulfils the City Council’s desire for a better sustainable mode of transit and encourages the citizens of Calgary to opt for a healthier way of transportation. Supporting more sustainable means of transportation ensures the preservation of the existing neighborhood, and to meet its demands, less energy is consumed. In addition, the surroundings and wildlife habitat impacts are being minimized through construction best practices such as the use of booms and working outside the fish spawning windows.
In this manner, there is a drastic improvement in the quality of life that Calgarian leads. The low impact rate on the environment further enhances the existence of Calgary City for more generations.
Calatrava beautifully embraced the vision of the Calgarian’s with his aesthetic design. Its linear lighting integrated into the double-helical structure, producing a downward illumination, creates a landmark ambience in Calgary.
The Peace Bridge helps move further towards a future of sustainable and vibrant cities with functional connections that tie them together. This encourages people to get out of their vehicles and use sustainable modes of transportation such as walking, cycling, carpooling, etc. Hence, the Peace Bridge profoundly fulfils the Calgarian’s daily requirements and envisions the city to have a better future.
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Mitanis, M., 2021. Constructing Calatrava’s Peace Bridge | SkyriseCalgary. [online] Calgary.skyrisecities.com. Available at: <https://calgary.skyrisecities.com/news/2017/05/constructing-calatravas-peace-bridge> [Accessed 17 June 2021].