U.S. standards for keeping bridges from collapsing when hit by ships hail from a different era.
They rely on half-century-old West German experiments on model ships for a key mathematical formula. Their minimum specifications cite the danger of empty 195-foot barges breaking loose from their moorings and drifting into bridges, a threat that seems quaint compared with the hulking 985-foot container ship that strayed off course after an electrical failure and toppled the Francis Scott Key Bridge in Baltimore last month.
And in 2020, international researchers warned that the standards sharply underestimate the impact of a head-on collision by a big ship into a bridge.
As federal investigators probe what caused the Baltimore collapse that killed six workers and shut down a vital U.S. port, some experts say the tragedy is shining a light on the need to bring bridge safety requirements into the modern era. “The design standards take a while to update,” said Mark Gaines, who oversees bridges as Washington state’s design engineer. “It’s unfortunate, but sometimes it takes something like this as a wake-up call to say, ‘Wow, is this really the right standard?’ ” There was nothing inherently wrong with the West German research, which was published in 1976, said Preben Terndrup Pedersen, a bridge strike expert and emeritus professor at the Technical University of Denmark. That early research had been focused on protecting reactors on nuclear-powered ships, and forms the basis for calculating the “ship collision impact force” on bridge piers in the U.S. specifications.
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Source – Stars and Stripes
But the numerical tools we have developed since then and the experience we have today are so much better,” Pedersen said. In a 2020 study in the journal Marine Structures, he and his colleagues found that U.S. specifications undercount the force of a collision with a large container ship by 40 percent and require far less resistance to ship strikes than the Eurocodes design standards used in the European Union. The study found the specifications were reasonable for calculating the force from some smaller ships. The U.S. bridge design specifications are developed and issued by the American Association of State Highway and Transportation Officials, or AASHTO. Federal regulation requires that bridge designers use them on national highways. Officials at the U.S. Department of Transportation consult on the standards, but don’t have a vote on what they include, which is set by the association of state officials.
Read more at: https://www.stripes.com/theaters/us/2024-04-18/baltimore-bridge-collapse-safety-standards-13589588.html
Source – Stars and Stri
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