By Marilyn Thompson
The award-winning Mistissini Bridge in Quebec, Canada, is the world’s first glued laminated (glulam) semi-continuous arched wood bridge. Spanning 525 feet, the bridge brings together innovative design, sustainable building practices, and a long-term investment in local business. Stantec, an international professional services design company, chose glulam to take advantage of locally sourced timber from the region’s vast natural resources. The bridge is a sterling example of how the innovative use of glulam can successfully combine design, safety, durability, and sustainability principles.
Glulam is advantageous as a building material because of its strength and performance. Denis Lefebvre, senior associate at Stantec who served as discipline manager, designer, and examiner during construction of the Mistissini Bridge, used glulam wood in part to overcome the project’s unique challenges. Construction needed to be completed under strict guidelines: The Mistissini Bridge was required to be environmentally sustainable, carry a carbon negative footprint, and weather the difficult environmental conditions of the region.
Gracefully spanning the Uupaachikus Pass, the bridge was commissioned on behalf of the local Cree Nation to expand socio-economic development in the region by allowing easier access to a commercial gravel quarry and residential zones. Lefebvre sought a bold new design based on the unique geography and resources available in the Mistissini region.
Lefebvre began with a unique geometric design. Laminated wood was formed into four sections of straight beams. Each beam was supported by a series of semi-continuous arches with pivot-type connectors, and then attached to the arches with concrete pilings with structural trunnions. A waterproof road deck was created from a bituminous coating, marine plywood, and many sheets of membrane to prevent damage from water penetration and long-term exposure to harsh weather. Finally, at the request of the Cree Nation, a steel guardrail was installed for safety along the perimeter.
By using glulam beams, Lefebvre eliminated the need for expansion joints over the span of the bridge. He instead opted for fixed bearings, which proved advantageous in several ways: they reduced seismic effects, provided a more economic price point for construction costs, and are projected to provide a higher level of durability in the long run.
Every opportunity was taken to minimize the bridge’s ecological footprint. Stantec evaluated three design proposals to compare wood with steel-wood and steel-concrete mixes. In a study released by Stantec, the CO2 equivalent emissions for using wood came to -497. Equivalent emissions for a steel-concrete bridge were calculated at +969. A comparison of the available options using the Athena Sustainable Materials Institute standards showed that the Mistissini Bridge “represents 1,472 tons of CO2-equivalent emissions less than steel and concrete, an amount equal to the CO2 emitted in the combustion of 640,000 liters of gas.” The result was a structure that carried a carbon negative footprint (http://nordic.ca/data/files/article/160-Metre-Long-Wood-Bridge-IHF2014_FINALE_Stantec.pdf).
According to Lefebvre, “Wood can be considered a carbon sink only if it comes from a sustainably renewed forest and the life expectancy of the structure is sufficiently high (generally 100 years).”
Chantier Chibougamau, sister company of APA-member Nordic Structures and located in northern Quebec, manufactured and supplied the lumber for the project. Chantier Chibougamau was chosen, in part, because its headquarters are only about 56 miles from the Mistissini Bridge, ensuring that all wood used was locally sourced from nearby sustainable forests.
Ultimately, the Mistissini Bridge will play an important civic and cultural role by increasing mobility and access for local communities. The bridge achieved the goal of marrying innovative design, sustainability practices, and a long-term investment in local business.
It also offers a striking visual connection to the land around it. “The bridge reflects nature around Mistissini,” said Lefebvre. “Constructing a wood bridge is more symbolic to the community than other kinds of bridges, such as steel or concrete.”
The Mistissini Bridge garnered several awards, including the l’Association des firmes de génie-conseil – Québec “Laureat” for infrastructure and transport and the Association of Consulting Engineering Companies’ “Engineering a Better Canada Award.”
Marilyn Thompson is market communications director and corporate secretary for APA-The Engineered Wood Association (https://www.apawood.org). She also represents APA on the board of the Canadian Wood Council.