Climate change could damage thousands of U.S. bridges, engineers say

Accra, Jan. 21, (UPI/GNA) – Bridges built
after World War II are susceptible to temperature variations, making them more
likely to fail because of climate change, two civil engineers have found.

Drastic fluctuations in climate, often
blamed on humans, could cause significant deterioration to tens of thousands of
steel-girder bridges across the United States, a study from Colorado State
University civil engineers Susan Palu and Hussam N. Mahmoud concluded.

They studied simple steel-span bridges
constructed with a deck on top of two girders and supported by concrete
pillars. The bridges were mass-produced during the highway boom in the 1950s
and 1960s.

Of almost 90,000 U.S. bridges studied, about
25 percent could fail within the next 20 years. Almost 30 percent of steel-span
bridges could fail by 2060, and nearly all of the bridges will failed by 2100,
the researchers predicted.

Researchers found a weakness in expansion
joints, which allow girders to expand and contract 3 to 6 inches as
temperatures rise and fall. The problem, they said, is that the joints, which
lie on the roadway and work like interlocking fingers, often clog with debris
and dust.

When the steel heats up, “the girder
wants to expand, but the joint is already clogged with debris,” Mahmoud
said.

Axial pressure on the girders, added to the
vertical weight of cars and trucks on the bridge, could cause steel fatigue,
leading to cracks in the deck and steel supports.

“When the steel can’t expand there is a
pushing-back on the girders,” he said.

As many of these bridges reach the end of
their intended life, climate-related stresses could cause them to fail sooner
than expected, authors said in “Impact of climate change on the integrity
of the superstructure of deteriorated U.S. bridges,” published in PLOS
One.

Bridges in the Northern Rockies and Plains,
Northwest and Upper Midwest are the most vulnerable to hastening deterioration.
North and South Dakota were states in which the most bridges were at risk, the
study found.

Expansion joints are a maintenance problem
compounded by the number of bridges with similar features, said Boston-based
Andy Herrmann, former president of the American Society of Civil Engineers and
the Structural Engineering Institute, who was not connected with the study.
Herrmann said regular inspections flag debris-filled bridge components.

“It’s a maintenance problem that could
be accelerated by climate change, and we have to stay on top of it,”
Herrmann said, adding that in old bridge extension joints theoretically could
be replaced or shaved down to adjust to raising temperatures.

The Federal Highway Administration inspects
bridges every two years for damage that could cause catastrophic failure. The
program began after the 1967 collapse of the Point Pleasant Bridge over the
Ohio River that killed 46 people after a suspension bar failed.

Another fatal bridge collapse from a design
flaw came in 1983, when a section of the Mianus River Bridge in Connecticut
gave way because of rust, killing three people.

Almost 615,000 bridges exist in the United
States, and almost 40 percent of them are 50 years old or older. Bearings and
expansion joints get clogged with dirt, grit and salt, engineer Herrmann said.
Engineers designing bridges now cover the joints, allow for expansion in the
bridge’s support or use a design that doesn’t collect debris.

If temperatures in the United States rise by
even 1.8 degrees Fahrenheit, clogged expansion joints will put added stress on
these bridges in some parts of the country that already are at the end of their
useful life, Mahmoud said.

Fixing bridge structural failures increases
commuter time and can cause social and economic losses when bridges are closed
for significant repairs.

The American Society of Civil Engineers’
2016 “Failure to Act” report estimates that from 2016 to 2025,
“each household will lose $3,400 each year in disposable income due to
infrastructure deficiencies.”

“We still have all those old bridges
out there that have to be maintained rehabilitated and eventually
replaced,” Herrman said. “It all comes down to money.”

As for new bridges being built, civil
engineers need to account for climate change and stronger designs that can
withstand increased flooding, seismic activity and temperature fluctuations,
Mahmoud said. Adding these contingencies is a growing area of study in civil
engineering, he said.

Palu was pursuing a master’s degree in civil
engineering when the work was conducted, and Mahmoud is an associate professor
and chair of the American Society of Civil Engineers’ Steel Bridges and Fatigue
and Fracture committees.

“Historically, these steel bridges have
done well, and we have had limited failures, but going forward, engineers need
to factor in extreme weather and higher temperatures,” Mahmoud said.

GNA

Loading...