Monday, 30 January 2012 13:41
January 30, 2012
The U.S. is facing a mounting crisis as more and more bridges are designated as structurally deficient, requiring a significant amount of maintenance work cash-strapped state governments cannot afford.
Bridges throughout the nation are falling into disrepair, having been constructed decades ago during a construction boom. The recession significantly hampered state and local government officials' ability to address such issues, and now the federal government is scrambling to ensure that critical repair work is done to affect bridges and roadways.
More than 18,000 bridges in the U.S. have been classified as fracture-critical bridges, an unwelcome designation that has prompted fears among engineers about the nation's increasingly dilapidated system of roadways. Perhaps more worryingly, some 8,000 bridges in the U.S. are "structurally deficient," according to data from the U.S. Federal Highway Administration.
There is some confusion among the general public about what, exactly, would spur engineers and other safety experts to question the structural integrity of thousands of U.S. bridges. Experts contend that there are myriad potential issues plaguing the nation's bridges, and that corrosion, wear-and-tear and old age are continuing to prompt questions about whether they are safe for traffic.
The burgeoning battle over the nation's bridges is evident in New York, where lawmakers have tussled over the Tappan Zee Bridge. The bridge connects Rockland and Westchester counties and more than 140,000 vehicles travel across it each day. However, it is listed as fracture-critical, meaning that the failure of one of the bridge's major components would essentially destroy the entire structure.
The Associated Press reports that New York Governor Andrew Cuomo has earmarked more than $5 billion to replace the bridge, but critics have questioned whether the state can actually secure such a hefty chunk of financing. The state hopes to construct a replacement bridge that would run alongside the current Tappan Zee, but lawmakers are unsure whether the project will begin as planned.
University of Minnesota College of Design dean Thomas Fisher asserted that fracture-critical bridges require more intensive routine inspections. Unlike other kinds of structures, such bridges need to be routinely inspected by credentialed engineers who can assess whether any safety threats are looming.
"Fracture-critical bridges work fine if maintenance is perfect and everything goes as designed," he said. "But if you start to change anything, they become very fragile. Their fracture-critical nature means they don't give any warning at the point of collapse. It is sudden and catastrophic."
Perhaps one of the most famous instances of the devastating consequences of not properly inspecting a fracture-critical bridge is the fate of Minneapolis' I-35 bridge, which collapsed in August 2007. Thirteen people died during the incident, while another 145 were injured, according to Bloomberg.
Many of the nation's fracture-critical bridges were constructed in the 1960s and 1970s, and some are nearing the end of their projected lifespan. American Society of Civil Engineers president Andrew Hermann said that the average fracture-critical bridge could function optimally for roughly 50 years.
"These bridges have an amazing safety record to this point, but they are getting old and have to be watched," he warned.
However, many state governments are struggling to keep up with regular maintenance and safety inspections. With tax revenue depleted, they have little available funding to pay for the inspections of bridges rated as structurally deficient. The American Association of State Highway and Transportation Officials states that such structures need "significant maintenance and repair to remain in service and eventual rehabilitation or replacement to address the deficiencies."
Fracture-critical bridges must be inspected more often than highway bridges, but they are also more costly than other kinds of assessments.