Bridging the gap of weather-testing stay cables

- Ottawa, Ontario

NRC researchers are ensuring that Canada's bridges are resilient to climate change

Canada is home to some of the largest and most heavily used cable-stayed bridges in the world. Bridges such as the Champlain Bridge in Montréal are critical transportation links. The stay cables that secure them are designed to support thousands of tonnes, and their safety has been researched extensively, but climate change is increasing their exposure to adverse weather conditions—ice, rain, snow, and wind. Researchers from the National Research Council of Canada's (NRC) Aerospace Research Centre and Construction Research Centre are working to ensure Canada's bridges remain resilient.

The Aerospace Research Centre has been studying stay cable aerodynamics for more than 20 years. In conjunction with the Construction Research Centre, this recent research on bridge cables will improve the understanding of rain-wind vibrations and will allow development of better simulations, responses, and predictions of the level of damping required to mitigate the observed vibrations. The combination of rain and wind can be especially harmful, and over time, it could have an impact on a bridge's safety and life span.

NRC researchers are addressing this gap in bridge cable research as part of the Climate-Resilient Buildings and Core Public Infrastructure Initiative funded by Infrastructure Canada for $42.5 million. The results of the research will be used to make recommendations on how to integrate climate resiliency into the Post-Tensioning Institute design code for stay cables.

Custom-built structural solution

Vibrations caused by rain and wind are challenging to test in a laboratory setting because rain needs to be tested at full scale. Rain droplets cannot be accurately simulated at sizes that are smaller than a drop of water, so testing requires a tunnel that can accommodate a section of a real size bridge cable. There are a limited number of facilities with that capability, and the Aerospace Research Centre's 9-metre wind tunnel is the only one in Canada.

"Most wind tunnels are limited by the size of their test section. When you introduce rain and wind conditions, you need to scale down the geometry to reduce blockage, but you can't properly scale rain droplets. A wind tunnel with a larger test section can provide a more accurate simulation."

Annick D'Auteuil, Research Officer, Aerodynamics Laboratory, Aerospace Research Centre

In 2017, the Aerospace Research Centre began designing and building a new dynamic rig for the 9-metre wind tunnel. The custom-built steel structure is capable of accommodating a 5-metre-long inclined cable model with diameters up to 0.32 metres, wind speeds up to about 70 km/h and a rain intensity around 10 mm/h. The dynamic rig enables researchers to change the various parameters that affect the cable's aerodynamics, such as the cable's inclination angle and wind yaw angle.

Informing codes for safer transportation

Research using the Aerospace Research Centre's 9-metre wind tunnel will help ensure that new bridges are resilient, and existing bridges can be retrofitted to extend their life. The findings and recommendations stand to inform future bridge and safety codes.

"We want to learn from what we have observed about how vibrations caused by wind and rain can impact bridge cables. We plan to use those results to build safer and more resilient infrastructure."

Marianne Armstrong, Manager, Climate-Resilient Buildings and Core Public Infrastructure, Construction Research Centre

Climate change can increase the severity and frequency of extreme weather events, potentially impacting the structural integrity of key infrastructure. With increased risk, bridge designers are seeking to understand the aerodynamic behaviour of their structures under a variety of weather conditions. The NRC's facilities and expertise enable the testing of inclined stay cables in all weather conditions, helping ensure that our clients' bridge designs are capable of withstanding the rigours of a changing climate.

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