Leveraging Bridge Aerodynamics to Achieve Climate Resilience

Long-span bridges are critical infrastructure in our transportation network. They offer convenient routes for daily commutes, foster economic growth, and provide safe travel over a range of obstacles, amongst many other social and economic benefits. However, the changing climate, including increases in wind hazard intensity and frequency, presents a challenge to long-span bridges: their safety, performance, and serviceability are quite sensitive to it.

In April 2024, IABSE held a symposium in Manchester, United Kingdom. The overall theme of the conference was Construction’s Role for a World in Emergency. 

As part of this conference, RWDI’s own David Hamlyn, Senior Project Manager – Associate, and Tung Nguyen, Scientist Engineer – Associate, presented on how the wind can influence long-span bridges and how understanding potential risks is a crucial component to ensuring their climate resilience. They also discussed the benefits that early-stage aerodynamic and climate consulting provides in achieving climate resilient bridges.

We spoke to both David and Tung to get the most important takeaways from their presentation.

Q: What is bridge aerodynamics and aeroelasticity?

Tung: Bridge aerodynamics refers to the interaction between the wind and various components of the bridge structure, which could generate adverse wind flow behavior leading to instabilities of, for example, the bridge deck or pylons, as well as wind loading issues. Bridge aeroelasticity determines how the bridge reacts to wind loads, such as structural displacement or discomfort for users.

Q: What are the challenges facing the aerodynamic performance of bridges?

David: When designing new bridges, you have to consider the potential for aerodynamic instabilities. Doing so helps minimize the potential for adverse impacts, including the risks of vortex-induced oscillations, flutter, and galloping. If not accounted for in the design, these issues can lead to discomfort for bridge users or excessive loading, and in the worst-case, failure of the bridge.

These challenges are particularly prevalent in existing bridges, as upgrades and maintenance work may affect the shape of the bridge deck and, as a result, the aerodynamics of the structure. This can potentially introduce new wind-related issues onto an existing bridge. A significant portion of existing bridge stock is aging and needs maintenance or upgrades to meet modern standards. Examples are the inclusion of improved traffic separation barriers or taller bridge parapets, all of which have the potential to change the aerodynamics.

When conducting the necessary maintenance and upgrades, the bridge's shape will be impacted potentially both during and after construction. Appropriate testing can help ensure bridge aerodynamics are accounted for in the process so the upgraded bridge continues to perform as intended.

Q: How does climate change affect bridges and their aerodynamic performance?

T: Bridges are designed according to certain wind speeds estimated at the time of their construction. The design wind speeds are determined based on the statistical analysis of historical records of wind speeds measured at meteorological stations. However, we know one of the effects of climate change is shifts in wind behavior, including the frequency and severity of windstorms. As a result, obtaining updated information and designing for resiliency and the potential for future changes in both wind conditions, as well as the overall climate is crucial when rehabilitating existing bridges as well as constructing new ones. We also need to account for climate change increasing the frequency and severity of ice accretion events – this can influence a bridge’s aerodynamic performance, such as when fences are iced up.

Q: What are the benefits of early-stage aerodynamic and climate consulting in delivering climate resilience for new & existing long-span bridges?

D: Aerodynamic and climate consulting provides several benefits in relation to delivering climate resilience. Initially, it helps ensure bridges will perform as expected, pedestrians will not experience discomfort, and the bridge itself will not experience excessive wind loads. Allowing for the changing climate in the design process helps provide resilience against future changes to the wind climate that the bridge structure will experience.

When designing new bridges, leveraging early-stage consulting can ensure bridge aerodynamics feeds into the developing design, allowing for the creation of a more efficient structure. This can reduce the potential for late-stage design changes and streamline construction stage planning and execution. All of this contributes to cost savings as well as a reduced carbon impact through more efficient work or reduced use of materials.

Q: Why is the rehabilitation and retrofitting of existing bridges crucial?

T: Aging bridge stock, in many instances, needs to be retrofitted or replaced to ensure the bridges can meet the current demands being placed on them, which are different and typically larger than the original demands. For instance, many bridges must now support heavier traffic volumes and many standards also require the inclusion of additional traffic and safety barriers.

Building new bridges carries a significant cost in comparison to the cost of retrofitting existing bridges, both from a strictly financial perspective as well as with respect to carbon. 

Bridge rehabilitation, to meet current demands and standards, leverages these existing assets and takes less time than new construction. Of course, efficiency in the rehabilitation and retrofitting process is crucial to ensure the design adjustments can be made smoothly. It’s here that assessment of the aerodynamics of temporary works schemes involving encapsulation using tarping feeds into the process. This helps ensure efficient and safe rehabilitation work on the bridge, minimizing the likelihood of bridge closures and their impacts on traffic and carbon emissions.

Q: What is the number one takeaway from your presentation?

D: Ensuring our bridges meet the demands society places on them as well as applicable standards requires thoughtful and effective design choices. The extent of these choices, including whether the existing bridge will undergo maintenance, a retrofit, or be replaced entirely, can vary.

However, whenever these design choices alter the shape of the bridge, it is vital to consider the potential aerodynamic effects they will have. Aerodynamic testing uses the best available information to make informed decisions and help ensure the bridge performance will meet demands, standards, and expectations.