Bridges in the US and other high-income countries are ageing and deteriorating. Last year, a large portion of an Italian bridge built in the 1960s collapsed, killing more than 40 people.
One of the most common problems involves expansion joints. These allow sections of a bridge to swell and shrink in warmer weather without weakening the structure. But they cause major structural problems if they malfunction.
Hussam Mahmoud at Colorado State University and his colleague decided to model the effects of increasing temperatures on steel bridges around the US.
In particular, they focused on what would happen when joints that are clogged with dirt and debris are exposed to the higher temperatures expected in the years ahead as the climate warms. Clogging is a common problem, especially in deteriorating bridges, but it is costly to address.
Bridges at risk
This clogging prevents sections from being able to safely expand and strains parts of the bridge that weren’t designed to withstand the resulting load.
Mahmoud analysed data on the condition of around 90,000 bridges across the US and modelled how the expansion joints would be affected under temperatures predicted for the next 80 years.
They found that current temperatures aren’t extreme enough to cause a problem, but one in four bridges are at risk of a section failing in the next 21 years, rising to 28 per cent by 2060 and 49 per cent by 2080. Almost all are set to fail by 2100.
“These failures are very serious,” says Mahmoud.
Bridges are designed to allow load to be distributed if part of it fails. However, this study focused on failures in the main load carrying part of the structure, meaning the section would either collapse outright or require major work to fix.
Lihai Zhang at the University of Melbourne in Australia says that developed countries around the world are facing similar issues as their infrastructure ages. In the US, two in five bridges are 50 years old or older. Many were never designed to last for so long.
Zhang’s work suggests that, in addition to heat problems, climate change could also make these deteriorating bridges even more vulnerable because of stronger winds, greater rainfall and the effects of corrosive carbon dioxide in the atmosphere.
This is exacerbated by growing populations, more traffic and trucks much heavier than these bridges were first designed to accommodate, he says.