What will we learn from the Key Bridge collapse? Engineers ponder safety lessons

It’s a familiar pattern for engineering experts.

After a major disaster, the National Transportation Safety Board launches an investigation. Conclusions are drawn. Lessons are learned. Often, new regulations and safety protocols follow.

But the Key Bridge collapse, unique in many ways, poses a particular set of questions that could span multiple federal agencies.

It was the result of failures affixed to failures: a ship veering off course, seemingly unable to correct its path away from a support pier that was ill-equipped to repel it, with no tugboats nearby to assist and desperate, last-ditch efforts to warn the construction crew fixing potholes on the road surface. Six of that crew perished in the collapse.

“The Baltimore bridge lies in a special category,” said John Stanton, a professor of civil engineering at the University of Washington.

The Key Bridge spanned a large shipping channel, which made it susceptible to ship impacts and gave it “a particular niche along the curve of probability vs. consequence,” Stanton said.

“We would like to think of it as a low-probability-but-high-consequence event,” Stanton said. “Unfortunately, it was the second but not the first.”

In seeking to better understand the collapse, conversations with nearly a dozen engineering experts have identified scores of potential changes that might follow the Key Bridge disaster.

They include federally mandated reinforcement of support piers for bridges in shipping lanes, stricter rules for ships that pass beneath critical infrastructure on their way to or from port, enhanced requirements for tugboats to escort large ships, and relatively uncommon solutions such as bridge “collision detection systems.”

A bridge too far: Cost of upgrades will factor in

Gongkang Fu, a professor of civil engineering at the Illinois Institute of Technology, said that container ships have increased in volume significantly since the Key Bridge was designed.

“What has changed for bridge design since then? Not that much,” Fu said. “So right there, apparently there’s a gap somewhere.”

Bridge design goes by specifications, last updated in 2007, Fu said, and there’s no expectation for a bridge to be stronger than what those specifications require.

But Fu also questioned whether it would be feasible to design a bridge to withstand the type of allision, a moving object striking a stationary object, that occurred between the Dali and the Key Bridge, given how costly such fortification would likely be. He said the onus should primarily be on updating rules and regulations for ships.

“That doesn’t mean that we shy away from our responsibilities as bridge engineers,” Fu said. “We can improve, but I don’t think it’s going to be feasible to prevent that kind of thing from happening.”

The goal should be to design bridges that do not entirely collapse in the event of a ship strike, Fu said, similar to the way structures are designed to resist earthquakes.

Stanton agreed that financial constraints will be likely be a primary factor when it comes to devising better methods to protect bridges from ships. Physical barriers, such as concrete dolphins, are expensive, but Stanton said they likely protect against a standard human error by a ship operator or tugboat captain.

“Perhaps we should devise a system whereby the ships ... that have the potential for the greatest damage need a more secure approach,” Stanton said. “Maybe they have to post a [returnable] bond before ever coming into the harbor.”

Incoming? Sensors that detect approaching ships

Some experts have pointed to relatively novel “ship collision detection systems” as an inexpensive improvement that could potentially save lives.

Last week, during a Johns Hopkins University panel of experts webinar on the Key Bridge collapse, Susu Xu, an assistant professor in the department of civil and systems engineering, said bridges in shipping channels should be retrofitted with sensors on their decks.

In the event of a ship losing control, as it the Dali appeared to, Xu said the ship’s crew would be able to communicate with a “central system,” which would also be fed information by the bridge’s ship-detecting sensors, used to issue warnings to DOT and alert nearby bridges.

“Once they are activated by collision detection, it would immediately flash and change alarms on the bridge and also change the traffic signals so that people can be evacuated,” Xu said.

Assessing vulnerable bridges

For more than half a century, state departments of transportation have considered impacts from shipping vessels among the design criteria for new bridges over major shipping channels, said R. Shankar Nair, a civil engineering expert.

But Nair said that such considerations may soon become federally mandated, including mitigation measures that could range from strengthening piers enough to resist vessel impact, which he said was more easily done for river barges than big ships, or requiring concrete “dolphins” or man-made islands made of rocks and sand to prevent impact.

“A more immediate issue is what to do about existing vulnerable bridges,” Nair said. “There may (and certainly should) be a push to assess risk and initiate retrofit measures where appropriate.”

Nair added that strengthening piers will “not be practical in most cases.”

“Measures to protect piers from impact,” he said, “are more likely to be effective.”

Ben Conarck

benjamin.conarck@thebaltimorebanner.com

Ben Conarck is a criminal justice reporter for The Baltimore Banner. Previously, he covered healthcare and investigations for the Miami Herald and criminal justice for the Florida Times-Union.

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