And it's likely to get worse, not simply as a result of time and traffic, but due to climate change.
In a new study, a pair of engineers at Colorado State University
outlined the potential effects of climate change on the structural
integrity of bridges in the U.S.
The duo's research focused on the country's 80,000 "simply supported
steel girder bridges," a design common since World War II that consists
of longitudinal beams spanning two piers.
Girder bridges also feature expansion joints, which link bridge spans
and allow the bridge to expand and contract with seasonal temperature
fluctuations. Because these joints regularly clog with debris and must
be cleaned, girder bridges require routine maintenance.
As a result of poor oversight and limited transportation budgets,
maintenance has been deferred on thousands of bridges around the
country. Clogged joints prevent bridges from properly expanding.
Engineer Hussam Mahmoud and his research partner Susan Palu, who
recently graduated from Colorado State with a master's degree in civil
engineering, reasoned that as global warming continues and temperatures
rise, bridges will be subjected to greater heat stress.
Heat stress can cause bridges to buckle and crack -- structural
defects that can become exacerbated by the stress of passing cars and
trucks. All this stress is made worse by clogged joints.
Using their understanding of thermal heat stress, Mahmoud and Palu
built a model to predict the effects of rising temperatures on the
structural integrity of simple girder bridges. The researchers suggest
bridges built in cooler climates will be most vulnerable to climate
change, as they weren't designed to withstand as much summertime
expansion.
According to the study, published this week
in the journal PLOS One,
bridges in the Northern Rockies and Plains, Northwest and Upper Midwest
are likely to experience the greatest increase in thermal stress.
Bridges in the Northeast and Southeast will be less susceptible.
"We surprisingly find that potentially most of the main load carrying
girders, in the analyzed bridges, could reach their ultimate capacity
when subjected to service load and future climate changes," the
researchers wrote in their paper.
The study's authors hope their findings will move transportation and
infrastructure policymakers to account for the effects of climate change
when prioritizing repairs.
"We as engineers must start to look beyond what we have initially
been taught on how to analyze systems and start to think about what
climate change is going to do to our understanding of component-level
behavior and system-level performance," Mahmoud said.
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