By Marwan Nader and Hayat Tazir, Contributing Authors
Montreal’s new Samuel De Champlain Bridge stretches more than 2 miles across the Saint Lawrence River. Building the cable-stayed bridge provided many challenges, and when it opened in 2019, the project had provided several lessons about recent trends in bridge design, planning, construction, and operations.
And, of course, the weather.
Montreal winters are brutal, with temperatures that often don’t go above freezing. Being outside for extended periods can be uncomfortable and hazardous, which means, when it comes to working outdoors, employee recruitment and retention can be an obstacle.
Carrying out precision work, such as welding and concrete pouring, is also a challenge. Yet, the project’s tight timeline meant that we needed to keep moving forward, even during the winter.
Three ways in which the team met the project’s winter-specific challenges were:
Maximizing the Use of Precast Structural Members
The decision to use precast concrete was driven by the accelerated construction schedule. For such a large-scale bridge, the trade-off between the use of precast concrete segments and the difficulty in transporting these large loads to the construction site through congested downtown streets required careful consideration.
For the Samuel De Champlain Bridge, which is colloquially known as the Champlain Bridge, the team employed both a precasting yard and an on-site precast plant.
The on-site pre-cast plant was facilitated using specially configured barges that were equipped with a crane to carry the heavy precast foundation elements from the plant to the bridge site.
This required an upfront investment in a shop and equipment, as well as a plan to build the plant and have it certified in time.
Having a plant on-site allowed the use of massive concrete segments that could never be delivered through Montreal’s surface streets from a remote facility. Even using a plant located elsewhere on the St. Lawrence River would have been problematic because of the risks posed by transporting large, heavy elements long distances by water, and because the river is not easily navigable for several months out of the year.
The benefits of the on-site precast plant were numerous for workers and their handling of the materials inside a heated building, where pouring concrete and placing rebar could be controlled.
The lesson: plan, plan, plan, and then plan some more and execute. It was important to have the precast plant design, construction, and certification under control. Now, construction could be accelerated.
Protecting the Bridge from Road Salt
Montreal winters require the use of road salt—vital for keeping the streets safe during icy and snowy weather. But road salt can also corrode steel structural members, as well as work its way into cracks in the reinforced concrete, attacking the rebar. It’s like poison for bridges.
Road salt was one of the primary causes that shortened the original Champlain Bridge’s service life before its time. To deal with this threat, the new bridge was designed to protect it from road salt.
One solution was to reduce the presence of salt water through innovative drainage designs. This prevented the water from forming puddles in areas in and around the bridge. Special formulations for concrete were also employed; these formulations incorporated additives that effectively reduced infiltration of water through cracks. All rebars in the deck are stainless steel, which also protected the bridge against salt water.
In all aspects of bridge engineering, a good designer must consider the potential threats, and then plan ways to mitigate those threats.
Ice Fall Protection
Winter in Montreal often means freezing rain. Ice coats everything, including the stay cables of the Samuel De Champlain Bridge.
To prevent ice build-up on the stay cables, which could, in turn, lead to ice sickles falling onto pedestrians and cars, the designers tested a variety of ideas in the wind tunnels and laboratories to estimate the level of ice accretion. The outcome was to use ring ribs (instead of helical) on the stay cables to reduce the size of the ice sickles, posing less threat to the traveling public.
Tight Schedule for Completion
The project was completed on schedule because the team—from the engineers and contractors to the fabricators and project owners—cooperated and communicated.
This teamwork came to the fore when the design-build team recognized that the construction needed to be accelerated by three months to meet the schedule. Having key team members located at the project site helped solve this problem. Engineers and builders put their heads together and came up with about 20 ideas for expediting the schedule; each solution was evaluated, and the most optimal plan was selected.
The new plan involved the construction of the cable-stayed portion of the bridge crossing the Saint Lawrence Seaway. Because the waterway is vital for the United States and Canada, a firm rule had been established – no temporary works in the ship channel. But how could building the cable-stayed bridge be supported without encroaching the waterway?
The team looked for an alternative way to build the cable-stayed bridge quickly. The original plan was to build the deck from just the central support tower, which is located on the north bank of the shipping channel.
The answer? Build the deck from the south side as well, supported by a second smaller, temporary cable-stayed structure. This approach employed a king post that stood atop the deck and was located on the channel’s south bank.
Construction crews placed the deck segments of the bridge, suspending them temporarily over the channel before the stays from the permanent central post, on the north side, were connected. Working on the bridge deck from both direction accelerated the project.
Teamwork was critical to the completion of the bridge. This sort of cooperation sounds easy on paper, but anyone attempting to deliver a project of this caliber would find that it’s not likely to happen if communication is solely dependent upon phone calls, texts, Zoom calls, and email. It’s imperative to get everyone working out of the same room.
Meeting the Community’s Needs
The Samuel De Champlain Bridge is one of the most important transportation links in Montreal, connecting the Island of Montreal to the South Shore of the St. Lawrence River. It’s a major commuting route for workers, seeing an estimated 59 million crossings a year.
But, for large metropolitan communities, signature bridges such as the Samuel De Champlain are far more than just a piece of infrastructure. Consider how the Golden Gate Bridge has, for nearly a century, helped to define the San Francisco.
The planned replacement of the old Champlain Bridge attracted significant community interest from those who were eager to share how they believed the new bridge should express the community’s values.
One way that the new bridge does this is through a multi-use path set aside for pedestrians and cyclists. In addition, the bridge’s center section carries a transit corridor for the city’s famed fully automated and driverless, electric-powered light-rail system, the Réseau Express Métropolitain. R&B
Marwan Nader, Ph.D., P.E., Eng., P.Eng., is senior vice president at TYLin, based in San Francisco. Hayat Tazir, P.E., Eng., is associate vice president at TYLin, located in Montreal, Canada.
