WASHINGTON (7News) — Baltimore’s Francis Scott Key bridge disaster has highlighted a common structural vulnerability in thousands of American bridges. More than 17,000 bridges lack structural redundancy, just as the Francis Scott Key Bridge did.
Engineers call these bridges "fracture critical," meaning if one structural support fails, the entire bridge can collapse. The National Transportation Safety Board (NTSB) immediately identified this lack of structural redundancy as a factor in the Key Bridge’s failure. When the 116,000-ton cargo ship Dali struck a bridge support column, the entire bridge collapsed in a domino effect captured on camera.
“That would likely cause a portion of or the entire bridge to collapse. There’s no redundancy,” NTSB Chair Jennifer Homendy said.
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Fracture critical bridges, those built without structural redundancy, are scattered throughout the country. Most were built between the 1950s and 1970s as the U.S. completed its interstate highway system.
INTERACTIVE MAP OF FRACTURED CRITICAL BRIDGES ACROSS THE U.S.
The Woodrow Wilson Bridge connecting Maryland and Virginia over the Potomac River and the Chesapeake Bay Bridge are among the busiest fracture-critical bridges in the D.C. area, according to Federal Highway Administration records. Both bridges have ‘adequate’ pier protection systems according to state bridge inspections reviewed by 7 News. Both bridges share the same structural and pier protection rating as Baltimore’s Key Bridge did the day it was hit and collapsed.
“When you’re designing new bridges you may make the piers robust enough that they can take a hit,” bridge and structural engineer Andy Herrmann said.
Herrmann, who served as the American Society of Civil Engineers president, noted that it is increasingly difficult to design adequate and affordable protection for aging fracture critical bridge piers. That work is complicated as the ships passing below these more brittle bridges grow larger and more common.
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“If it was designed today, it probably would have had much more robust protection of the bridge,” Herrmann said of Baltimore’s Francis Scott Key Bridge.
The NTSB chairwoman made a similar statement to Congress, telling the House Transportation and Infrastructure Committee that a bridge that began operations in 1977 – as Baltimore’s Key Bridge did – would be built to a different standard if built today.
“States and bridge owners should be evaluating, especially with older bridges, what is going through their waterways now, what is the risk, and how should they address that,” NTSB Chairwoman Homendy said.
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