The shifting landscape of bridge design and construction in Canada.
By Jianping Jiang and Keith Holmes
The way we design and build bridges in Canada continues to evolve. The introduction of new technologies and techniques, incorporating active transportation, and the need for greater environmental adaptation, are among the new variables that we now consider. It has forced us to change the way we deliver these vital infrastructure projects for communities across the country.
These factors are helping us build structures that are more efficient in carrying loads, resilient to climate change, and provide greater overall functionalities for all users of our communities. From remote highway river crossings to busy inter-city transit passages, the new generation of bridges are providing greater value than ever before.
Evolving bridge landscape
Many of the bridges you see built in Canada, at first glance, don’t look much different than what has been built in the past. We still see the same primary structural forms, usually girder bridges with the occasional arch or truss or cable-stayed crossing.
However, we are also seeing a shift in designs to suit new priorities. For example, river crossings are trending to longer spans often with no piers in the river channel. This approach can mitigate the environmental impact of a pier foundation in a sensitive water course and reduce the risk of damage associated with extreme flooding events.
Project owners haven’t lost the desire to build bridges that have an aesthetic appeal, but the cost premium that this commands can make it more difficult to justify. Where we are seeing less conventional forms are often with projects of smaller scale, such as pedestrian bridges, where aesthetic design can be achieved without breaking the bank.
With renewed focus on the whole life cycle cost of our structures, we are seeing design solutions that reduce future maintenance. The best example is the reduction in deck joints, a perennial maintenance headache that owners would gladly avoid. Continuous bridge decks and integral/semi-integral abutments are now commonplace in all jurisdictions including those in more northern climates. This means designing to accommodate larger thermal movements and bridge owners accepting some pavement maintenance at the approaches (which is still better than deck joint maintenance).
But in the last 10 years (since the 2014 Canadian Highway Bridge Design Code), the biggest change for bridge engineers is in seismic design. The old “force-based” design approach (i.e., make it strong) has been replaced with a ductility approach (i.e., make it “stretch”) with a focus on post-earthquake performance (what is the damage, and can the bridge still be in service to carry traffic?)
One such example is the increased use of seismic isolator bearings to reduce inertial demands on bridge structures. Outwardly, a bridge may not look all that different, but how the bridge is designed and detailed has changed profoundly to accommodate seismic performance.
There are a few other changes worth mentioning as part of the evolution of our bridge designs:
- the increasing use of prefabricated bridge components to manage the costs, quality, and risks of site work;
- the implementation of a Service Life Design approach, typically for large projects, where the engineers are required to explicitly consider durability limit states to ensure the design will meet the prescribed service life; and
- the reuse of existing bridge foundations for replacement bridges to minimize environmental impacts and reduce construction costs.
Each of these changes has led the bridge design and construction communities to adapt their way of delivering solutions for project owners across the country.
Designing for all users
Accommodating active transportation is one of the biggest recent trends and includes integration of pedestrians, cyclists, and various new personal mobility options. While the loading is less, design for all users’ safety and accessibility is now more important than ever. This means:
- improved accessibility that considers a path’s grade and width for integration of all users;
- improved safety that considers the travelled surface, railings, lighting, and signage;
- improved convenience where alignments prioritize active transportation users; and
- improved comfort including consideration for people-induced vibration of bridges.
These changes not only apply to the finished product but are now also an important consideration during construction. Owners and engineers now engage in dialog with active transportation communities, finding construction solutions that can accommodate the community at each stage of the project.
To support engineers in designing bridges for active transportation, CSA (Canadian Standard Association) is currently developing a new national guideline, the Pedestrian, Cycling and Multi-use Bridge Design Guideline, to be published in 2023. We are fortunate to have a number of our team members actively involved in developing this important new national document.
With municipalities across Canada developing active transportation plans, and government funding being provided to support their implementation, the need to consider and integrate all users into bridge design will only increase in the years ahead.
Technology and innovation
The introduction of new technologies is impacting both the design and construction phases of bridges, creating new insights into the long-term performance and durability of the structure.
In the design phase, the adoption of 3D BIM for large design-build and P3 projects has improved communication, collaboration, optimization, and simulation. Using BIM, team members can work with an integrated model to better resolve the inevitable interdisciplinary challenges. And project stakeholders can access a visualization of the project, providing input on design and construction, and identifying potential stressors.
During the construction phase, the installation of remote sensors is helping contractors detect and monitor movements and vibrations. And once construction is complete, owners are using similar technology to continuously monitor the health of the structure over its service life. There is also a range of new construction materials being introduced that focus on creating a durable and resilient final product. These include high strength and high-performance variations of steel and concrete products, as well as stainless steel and GFRP (glass fiber reinforced polymer) rebar providing long-term durability and service life benefits.
At every stage of bridge design and construction, environmental impacts are being given greater consideration than ever before. Even though legislation is inconsistent in provincial and territorial jurisdictions across Canada, there are enhanced standards in place, and even more are expected.
As an example, right now the BC Ministry of Transportation and Infrastructure and Engineers and Geoscientists BC (EGBC) have mandated that all highway infrastructure including bridges use a climate change-resilient design approach as documented in EGBC’s new guidelines, Developing Climate Change-Resilient Design for Highway Infrastructure in BC. The upcoming 2025 edition of the Canadian Highway Bridge Design Code will further address the impact of climate changes on bridges with new and specific requirements.
Bridge designs, regardless of jurisdiction, are considering the evolving environmental conditions due to climate change. On major projects, such as the new Champlain Bridge in Montreal, we are seeing an extended bridge design life of up to 125 years before replacement. And on all projects, we are seeing creative solutions to “tread lightly” on our ecosystems. As example, girder launches, and demolition “de-launches” are increasingly commonplace and planned well in advance to minimize the impacts on in-water and riparian habitats.
What comes next?
As the focus on delivering bridge structures with longer lifespans and minimal environmental impacts continues, there are two key features that we expect will continue to emerge in bridge development in Canada.
First, we are seeing an increase in the use of Accelerated Bridge Construction. On busy routes that are particularly impacted by prolonged traffic disruption, some project owners are turning to innovative construction solutions. In Ontario, we have seen several projects use a Self-Propelled Modular Transporter to literally pick up and move a bridge superstructure into place in a matter of hours. While the capital investment can be higher, the trade-offs from a community congestion and interference perspective can make it a worthwhile consideration.
Second, there is the introduction of collaborative procurement models such as Alliance Contracting and Integrated Project Delivery. While both are still in their infancy in Canada, especially in relation to bridge projects, they offer an opportunity for greater collaboration among all project partners, and the opportunity for a result that provides the best value to the public.
There continues to be a lot of change in the design and construction of bridges in Canada, as new technologies create more efficient solutions, structures are built to withstand the impacts of climate change, and all team members work in closer collaboration. However, we believe that these changes, and our ability to implement them, will lead to the delivery of better bridges for those who use them.
[This article originally appeared in the July/August 2022 edition of ReNew Canada.]
Jianping Jiang is the national practice leader, Bridges and Civil Structures, at WSP in Canada.
Keith Holmes is the director of Bridges for BC/Yukon at WSP in Canada.
Featured image: The Flora Footbridge, crossing the Rideau Canal in Ottawa. (WSP)