NTSB chair Robert L. Sumwalt guest lectures in Forefronts of Civil Engineering graduate course
You know the saying, “He never met a stranger?” That’s Venkataraman Lakshmi. Passionate in his work as a professor in the University of Virginia Department of Engineering Systems and Environment, Lakshmi specializes in hydrologic sciences and is outgoing by nature; he’s the kind of guy who can easily strike up a conversation with the person next to him on a plane.
That very scenario is how National Transportation Safety Board chair Robert L. Sumwalt wound up lecturing in Lakshmi’s Forefronts of Civil Engineering class at UVA. Lakshmi brings a different speaker each week to the graduate-level course.
The chance meeting was three years ago, when the two men were traveling to Washington from Columbia, S.C. At the time, Lakshmi was on the faculty at the University of South Carolina. His office was in the building next to another one named for Sumwalt’s grandfather, a civil engineering professor who became dean of the engineering school and later president of the university.
Engineering, it turned out, was not Sumwalt’s own passion in life, he told the UVA Engineering students and faculty who packed into Olsson Hall 104 on Jan. 30. He chose aviation, flying for commercial airlines for nearly 25 years. Now, he leads the five-member board overseeing the federal agency responsible for investigating accidents related to modes of transportation, from airplane crashes to pipeline spills.
His topic, however, was about civil engineering — specifically what caused a concrete pedestrian bridge to collapse at Florida International University on March 15, 2018.
The bridge’s failure claimed six lives. One was a worker who was on the span attempting to repair massive cracks that engineers with the design firm insisted did not pose a safety risk. They were so confident of their design calculations and so persuasive in a meeting the morning of the collapse with officials from the Florida Department of Transportation, the construction firm, and Florida International that no one pushed to stop work or close the highway below. Five of those who died were crushed in their cars beneath the bridge.
The Safety Board’s investigators found three probable causes leading to the event or contributing to its severity, said Sumwalt, who, as a board member, does not actively lead investigations. First, they found engineers underestimated the load on the span and overestimated its strength. At one joint where two support members, one diagonal and one vertical, came together, the diagonal support exerted enough force to kick out the vertical member.
The resulting collapse was so abrupt, video shows the worker suspended in air as the concrete fell beneath him.
Sumwalt said they underestimated the load on this section of the span by 46%. “As a result, they did not use enough rebar to anchor this member coming down into the deck. They needed close to 18 square inches of cross section of rebar. They only had 4.8 square inches. They missed the requirement by 270%.”
Second, Safety Board investigators concluded that the peer review of the bridge’s design — a step that is supposed to catch the kind of mistakes that caused the collapse — was inadequate and missed the calculation errors.
Finally, there was a failure of every party involved in the project to recognize the danger and act to prevent a tragedy. Cracking in the concrete structure began during casting. As the cracks worsened dramatically in the five days between the time the span was placed on its pier supports and the collapse, engineers recommend repairs but continued to believe there was no safety risk. Critically, did not they seek an independent review to confirm their analysis and proceeded with repairs, despite not knowing the root cause of the cracks.
“Cracks in concrete up to about 16 hundreds of an inch wide are considered acceptable,” Sumwalt said. “There were cracks documented that were 40 times larger in width than the generally accepted tolerances.”
The National Safety Transportation Board announced the probable causes of the accident on Oct. 22, 2019, pending its final report. The design firm disputed the findings, blaming construction errors. The board rejected the design firm’s explanation.
Sumwalt believes arrogance and an overreliance on perceived expertise played critical roles in the loss of life that day.
“I don’t care where you fit on the totem pole, you have a moral obligation to call it when you’re uncomfortable with something,” he said, speaking to students in the room. “You are the future engineers. You have a professional responsibility to speak up.”
Responding to a student’s inquiry, Sumwalt said the most common factor leading to accidents his agency sees is someone not following procedures. “That’s an error that we see across modes, so thank you very much for your question.”
Lakshmi scheduled Sumwalt’s lecture before his regular class time and opened it to the entire department.
“Robert is passionate about improving transportation safety and serving the public, and an excellent communicator,” Lakshmi said of Sumwalt, who was appointed to the Safety Board in 2006 and became chair in 2017. “The themes he addressed are important and universal for all engineers, and I felt faculty and students should have the opportunity to hear him speak.”