BALTIMORE — After a cargo ship took out the Key Bridge, it wasn't long before Johns Hopkins engineering professor Michael Shields and his colleagues started crunching numbers.
“A colleague of mine, Ben Schafer, a co-investigator on this project, sent me an email and said, 'What do you think the actual probability of an event like this happening was?” Shields, an associate professor of civil & systems engineering, recalled. "And I did a quick, back of the envelope calculation and I came to the conclusion that it was probably a higher-probability event than we would've hoped for."
How much higher? Shields explains that the “target risk” set by the American Association of State Highway and Transportation Officials is “exceptionally low,’ - once every 10,000 years.
"So when we say it's higher risk, we say it's not 'exceptionally low.' It's still low; the probability of any given bridge collapsing on a given day is still very low. It's just not as low as we want it to be.”
But for now, that’s just a highly educated guess. Shields, Schafer, Rachel Sangree, a structural engineer and former bridge inspector, and a group of Hopkins students, are leading an “urgent risk assessment” to back that guess up with data.
It’s “urgent,” because we’re about to spend billions of dollars on a new bridge, and possibly on fixing up other bridges.
"And in that process, we need to make wise decisions. We need to have the right information at our fingertips when we make those decisions,”Shields said.
“The team’s findings will be crucial in reassessing and potentially redefining the safety standards for transportation infrastructure,” Schafer, a structurer engineer and professor of civil & systems engineering, said. “Given the estimated $1.7 billion to $1.9 billion cost to rebuild the Key Bridge and the potential billions needed to retrofit existing bridges, accurate risk assessment is vital to ensure the sustainability of society’s critical infrastructure.”
The team is studying bridges near major ports all across the country - including the Bay Bridge here in Maryland.
"You want to look at the traffic that goes under the bridge - what's the volume of shipping traffic -and then what is the probability that one of those vessels is gonna go aberrant, that it's gonna go off-course. And then, given that it goes off-course, what are the chances that it collides with the bridge?” Shields said.
“The U.S. has seen 17 incidents of major bridge collapse between 1960 and 2011, averaging one every three years. Between the exponential growth of mega freight ships and the surge in global shipping traffic, many of our bridges simply weren’t built to withstand the pressures of today’s maritime landscape,” Sangree said.
The U.S. Coast Guard agrees with that assessment. The agency is conducting its own risk assessment. Vice Admiral Peter Guatier told lawmakers during a hearing held by the House Transportation and Infrastructure Committee, "While we look forward to the results of these investigations, it is evident looking more broadly that the size and complexity of ships has grown over the years, placing greater demands on our marine transportation infrastructure that may not have kept pace with the increased risks that these vessels pose.”
The Hopkins investigators hope to report some preliminary results by the end of the summer. The entire study is expected to take about a year to complete. Then, they’ll bring their findings to the Governor’s office, the U.S. Department of Transportation, and any agencies that set design standards for bridges.
The Maryland Department of Transportation is currently doing a study on the Bay Bridge, looking at replacement and expansion options. But the primary purpose of the study is to ease congestion. In 2016, when the project was announced, then-Transportation Secretary Pete Rahn said, "The Bay Bridge can be maintained safely through 2065 with preservation and maintenance work; however, studies show that by 2040, motorists could experience up to 14-mile delays. This is the first step in a long process to address the demand for additional capacity across the Chesapeake Bay.”
After the collapse, current Transportation Secretary Paul Wiedefeld said findings from the Key Bridge collapse would now be considered in the study.
Shields says of his Hopkins study, "Certainly I would hope that the results that we get from this investigation can help to inform those type of decisions."
