But some engineers say Tuesday's collapse in Baltimore could have been avoided if the piers had been able to intercept, deflect or withstand such a collision. Ta. And some engineers questioned whether the bridge's piers had the proper shutoff devices, known by the more descriptive name fenders.
In bridge engineering, fenders range from simple pyramids of stone piled around the perimeter of towers to main structures filled with wooden slats designed to protect the bridge supports from water and collision damage. They range from concrete rings to concrete rings.
It was not clear whether such protection built around the bridge piers would be sufficient to prevent even a glance from the 95,000 gross ton container ship.
And U.S. Transportation Secretary Pete Buttigieg on Tuesday expressed doubts that any bridge could have withstood such a serious crash.
“This is a unique situation. I don't know of any bridge built to withstand a direct impact from a ship of this size,” he told reporters.
But a different perspective emerged in initial comments by investigators who will sort out what happened in the collapse.
National Transportation Safety Board Chair Jennifer Homendy said the protective structure will be part of the investigation into the collapse. “There are some questions about the structure of the bridge, the protective structure around the bridge and around the piers to prevent it from collapsing,” he said in response to a reporter's question.
“We know what the structure should be. Part of our investigation is how this bridge was built. We'll look at the structure itself. Is there some kind of safety? Do we need improvements? All of that will be part of our investigation.”
The Maryland Department of Transportation did not immediately respond to a request for comment on the design of the pier in Baltimore, nor would it say whether fenders were installed to protect the pier.
According to a 2018 report by the World Water Transportation Infrastructure Association, a science and technology organization, between 1960 and 2015, there were 35 major bridge collapses around the world due to ship or barge collisions; As a result, 342 people died.
The worst accident occurred in 1983 when a passenger ship collided with a railway bridge on Russia's Volga River, killing 176 people, according to the report.
Report authors Michael Knott and Mikel Winters said attempts to investigate and address the risks began in the 1980s, when “the frequency and severity of ship-bridge collisions increased significantly.” said.
A widely circulated video of the Key Bridge collapse drew attention to the tragic collapse of the upper bridge structure. However, technicians who reviewed the footage said it did not appear to be the culprit in the disaster. Rather, they said the superstructure failure was likely a secondary effect of collapse beneath the pier after the impact.
Engineers who reviewed images of the bridge before and after the collapse said they did not see any noticeable fender structure. Photos taken at the base of the pier showed only a much smaller structure, and it did not appear to be large enough to hold a large ship, some officials said. They said these structures may have served an entirely different purpose, such as preventing water from washing away and compromising the pier's foundation.
After looking at images of the bridge taken before the disaster, Benjamin W. Schaefer, a professor at the Johns Hopkins University School of Engineering, said, “If you zoom out even further, you can see large columns that seem to be defining the shipping lane. They are for guiding and are part of the bridge structure. Some would say they are protective structures. But I myself have never seen evidence of fenders.”
Shankar Naar, a structural engineer with more than half a century of experience and a member of the National Academy of Engineering, said that in some bridges, engineers are using “the alternative of making the piers very strong” instead of fenders. ” may be selected. But visual evidence so far suggests the pier was not strong enough to withstand the impact, they said.
Some engineers were stunned to see the structure's apparent weakness.
“This is a huge shock,” Dr. Nile said. “There's no way a bridge of that size and importance would collapse after being hit by an errant ship.”
The importance of strong fenders on piers was reinforced by a similar incident in 2013 when a 752-foot tanker collided with a support on the San Francisco-Oakland Bay Bridge. The National Transportation Safety Board's report on the crash said there was $1.4 million in damage to the shock-absorbing fender system, but assistance continued.
In other cases where a collision causes a complete or partial collapse, defects in the fender system are usually involved, says Matthijs Levy, a longtime structural engineer and co-author of Why Buildings Fall Down. he said.
“Usually it's a fender issue,” Levy says. “The fender isn't strong enough.”
According to the American Society of Civil Engineers manual's description of the Key Bridge, the 8,636-foot-long structure in Baltimore opened in 1977. The steel spans on it, a design known as a truss, can be susceptible to impact. Collapse itself – Damage to individual elements of a truss could theoretically cascade into a more widespread collapse. But that didn't appear to be the case in Baltimore, said technicians who reviewed the footage. The truss simply could not remain intact when the pier beneath it was removed.
Donald O. Dusenberry, a consulting engineer who has investigated many bridge collapses, said Tuesday's collapse “reveals just how vulnerable the piers are and what is being done to protect them if something like this happens.” “Was this done or should it have been done?” he said.
Dusenberry pointed to the issue of fender protection and said it is impossible to fully determine what is in place without looking at the bridge's structural drawings.
But images taken before the disaster showed small barriers rising around the bridge's piers, almost at water level, suggesting it was unlikely to be able to stop the large ship, he said. Stated. He said effective fenders must be far enough away from the pier to prevent a large ship's bow from colliding with it, and be large enough to absorb the energy of a collision. Assuming nothing has changed since the previous photo was taken, the visible structure doesn't appear to be doing its job, he said.
“Maybe the ferry or something will stop,” he says. “It's not a giant ocean-going cargo ship.”
One of the catastrophes that brought the issue of bridge collisions under scrutiny was the 1980 collapse of the Sunshine Skyway Bridge in Tampa, Florida.
The structure collapsed when the cargo ship hit the pier, causing part of the main span to collapse, killing 35 people. Seven years later, a shrimp boat crashed into a bumper that had been installed on top of the bridge that had been built to replace it.
While catastrophic collisions get the most attention, ship-bridge collisions are not uncommon and, according to a 2018 report, “can range from minor to major, but do not necessarily involve damage to structures.” They regularly cause damage that does not result in the collapse of buildings or loss of life.
Schaefer, a Johns Hopkins University engineering professor, said there is no doubt that fenders are important in preventing catastrophic collisions, but the size of the vessel hitting the bridge plays a key role.
“When people think of fenders, they think of something similar in scale and size to the supporting concrete structure itself,” Schaefer said. “So if the diameter is he's 30 feet, the fender might think he's 30 feet as well, right?”
He said the problem comes with trying to design protection for something as large as a container ship. “Can we design something big enough to turn a runaway freighter? Yes. Will it be of any practical scale? Probably not.”
Rather than building larger fenders, Schaefer said it's important to change course before the ship gets dangerously close to a pier or fender. “That would be the physical answer,” he said. “The better answer is to have the people and processes in place to ensure something like that never happens.””
