Climate crisis: US steel bridges could collapse


Earth is now the warmest, it's been in some 120,000 years. Eighteen of the last 19 years have been the warmest on record. And concentrations of carbon dioxide — a potent greenhouse gas — are likely the highest they've been in 15 million years and the consequences of such a globally-disrupted climate are many, and it's understandably difficult to keep track.

The changing climate also takes a physical toll on infrastructure. Materials such as steel expand in hot weather and contract again in cold temperatures but as extreme weather events become increasingly common, designs and materials are being tested to their limits.

US engineers are now turning their attention to the problems this can pose for the structural integrity of the country’s ageing transport network, which includes around 600,000 bridges.

Associate professor Hussam Mahmoud and Susan Palu focused their analysis on about 80,000 “simply supported steel girder bridges,” a design common in the US since the mid 1940s. These bridges suffer frequently from expansion joints. Expansion joints connect bridge spans and allow the structure to expand and contract as the air heats or cools. When joints become clogged, they prevent the bridge from expanding normally in response to higher temperatures. 

The study is the first to quantify the impact of potential temperature changes in conjunction with normal expected clogging of expansion joints. The researchers considered four different seasonal scenarios for temperature at the time of each bridge’s construction, along with projected average temperatures for the years 2040, 2060, 2080 and 2100. 

The projected temperature rises are the “radiative concentration pathway” greenhouse gas warming scenarios adopted by the International Panel on Climate Change in 2014.

Results indicate that bridges located in the northern portion of the United States, including the Northern Rockies and Plains, Northwest and Upper Midwest, are the most vulnerable to more pronounced increases in temperatures. They say one in four bridges are at risk of failing by 2040, and by 2060 this rises to 28 per cent.

“We as engineers must start to look beyond what we have initially been taught on how to analyse systems and start to think about what climate change is going to do to our understanding of component-level behaviour and system-level performance,” Dr Mahmoud said.

“Neglecting possible future climate change can jeopardize the integrity of many US bridges. Efficient maintenance to keep the expansion joints functional, on a regular basis, is vital to avoid undesirable thermal demands that will potentially be magnified due to climate change,” the study says. Learn more about Frederic Michel-Verdier on his profile page.

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