Extreme events from climate change are impacting bridges all over the world and the safety of its users.
Climatic extremes like intense heat, wildfires, freezing temperatures, and strong winds are straining all parts of the bridge, making it unstable and more prone to service disruptions due to damages or accidents. Making bridges resilient is imperative in the face of increasing threats from climate change.
According to the New Civil Engineer article, the high winds and heavy rain brought by storms that hit the UK have caused the temporary closure of its Queen Elizabeth II Dartford Crossing. The bridge is one of the many built during the bridge-building boom in the middle to the latter half of the 20th century when engineers widely applied steel-reinforced concrete and considered it an engineering innovation.
However, the effects of climate change are not yet embedded into the designs during this time. NCE, Arup fellow Richard Hornby, one of the engineers behind the Queensferry Crossing, says that although these bridges were built to last for 100 to 120 years, the designs considered the probability of events that occur once every 10,000 years, providing some guarantee of the bridge’s sturdiness.
Hornby notes that Eurocodes, established by engineering experts to ensure structures are designed and constructed robustly and safely and followed as the uniform building standards for all European countries, were used to build these bridges. However, the growing knowledge of the impacts of climate change means that these codes will dramatically change with each update.
He presents how extreme temperatures can impact the performance of bridges.
First, vehicles are now heavier, particularly EVs, and will increase the weight demands of bridges and roads.
High temperatures cause thermal expansions, increasing displacement demand on movement joints at the end of bridges. Although these bridges are built with a higher capacity to handle these demands, engineers will need to review the thermal expansion ranges of bridges.
Flooding can also erode the soil surrounding the bridge foundation, a process known as scouring, which can seriously compromise the bridge’s integrity. Hornby notes that threats from flooding will require new flooding and hydrological maps.
Regarding high wind speeds, Hornby says that most bridges were not designed to consider this but rather with large vehicle loads in mind. Bridge closure will likely be necessary in the event of strong winds.
A combination of extreme events occurring all at once, such as strong winds, rain, and freezing temperatures, could be detrimental to the bridge. Lee Cunningham, a University of Manchester reader in structural engineering and a chartered civil and structural engineer, explains, “If you’ve got extra ice formation on bridge suspension cables, you’ve got extra dead load on the bridge, in addition to greater area being presented to the wind, so increased wind pressures.”
This situation could affect new bridges in North America and Canada and should be considered in the design, Cunningham says.
Both engineers say that older bridge designs should serve as inspiration for future and more sustainable structures that can withstand climate extremes.
As for building the most resilient bridges, Cunningham says that brick-made bridges are at the top of the list due to the brick’s durability and the system’s simplicity. However, these are also the costliest to build because of the labor involved.
Both agree that additional infrastructure redundancies built into bridges will protect their lifespans in the face of extreme weather.
Still, it all boils down to how much money clients are willing to pay because the more engineering the bridge entails, the more expensive it is.
Source:
Pashby, T. (2024, January 18). The challenge of making bridges more climate-resilient. New Civil Engineering. Retrieved from https://www.newcivilengineer.com/latest/the-challenge-of-making-bridges-more-climate-resilient-18-01-2024/
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