The Minnesota Department of Transportation recently announced who will build the replacement Interstate 35W bridge, but the investigation into what went wrong with the original structure continues.
A slew of organizations are working to piece together why the bridge collapsed in August.
Terry Williams, spokesman for the National Transportation Safety Board, said the NTSB is leading the federal investigation and working with other parties involved, including faculty from the University.
One such party is Wiss, Janney, Elstner Associates Inc., a private engineering firm with whom MnDOT recently signed a $2 million contract.
According to MnDOT, WJE was contracted to work in coordination with the NTSB, but both organizations will be issuing separate reports.
Michael J. Koob is WJE’s project manager for the investigation. He said the firm has plenty of experience in conducting structural investigations. He arrived on the scene the day after the collapse and has been working with the NTSB.
“Although we are working with NTSB in the operation, we are retained by MnDOT, and we will issue a report,” he said. “That’s not uncommon. Decisions on who inspects what will be decided jointly. Things are already in the lab.”
Williams said the NTSB began its investigation as soon as it arrived on-scene, and should have people at the collapse site until early November.
“It’s an ongoing investigation that’s going to take approximately a year,” he said.
After the bridge collapsed, on-scene investigation began immediately, he said. As this initial phase nears its end, investigators will continue their work in the lab.
Williams also said the NTSB has worked with people from the University during the investigation.
Taichiro Okazaki is an assistant professor of civil engineering and leads the University’s team of engineers working on the investigation of the collapse.
He said although the team is no longer working at the site, they are still figuring out how to work with the other organizations involved. The team is trying to get pieces of the bridge into its lab in order to study them, he said.
“At the end, people will be doing a lot of computer simulations, but that knowledge would rely on the computers’ assumptions being accurate,” he said. “We are interested in studying the material and the structure itself to see what assumptions we actually should be using.”
Okazaki also said the team will issue some kind of report, but isn’t sure how far it will be able to go with its investigation.
The NTSB and WJE could retain elements of the structure that the University’s engineers would need in order to write a thorough report.
Earlier this month, a joint-venture bid between Flatiron Constructors and Manson Construction won the bid to build the replacement bridge. According to a MnDOT news release, this bid was chosen because it balanced price, time and the “road-user cost.”
None of the investigating organizations have leads or probable causes they are willing to discuss.
There might be more investigations done in the future. Koob said the NTSB is in charge of securing the collapse site.
“There’s really nobody allowed on the site except for the NTSB and us at this time,” he said. “Once the site is released, there’s going to be multiple consultants doing investigations on this.”
