A cone of science has descended over official interpretations about the cause of the March 15 pedestrian bridge collapse at Florida International University (FIU), as the National Transportation Safety Board (NTSB) investigates the incident that killed six people under the glare of national publicity.
The story, however, will likely emerge as an example of how engineering and construction can go wrong, especially in the context of the university’s leadership in construction management and engineering programs, and understanding how innovations in building practices and technologies should be encouraged, but with safety safeguards.
FIU’s president and board of trustees met on April 12 for the first time since the tragedy for a retreat at Coral Gables. Trustees started the meeting with a moment of silent for the collapse victims.
Then there was silence about the incident itself, with FIU president Mark Rosenberg and the university’s lawyer telling local NBC 6 TV that they needed to stay silent under NTSB guidelines.
“There could be a point in time during the investigation that the NTSB begins to lift the shield, but between now and then, we’re cooperating the best way possible . . . and that is to be a party member to the investigation,” the school’s general council, Carlos Castillo, said in the broadcast interview.
“We’re at the table with the NTSB and we’ve made the decision to do that precisely because we want to get to the bottom of what caused the bridge collapse,” he said.
Miami-based contractor MCM, in partnership with FIGG Bridge Engineers, designed and built the structure, part of a $9.3 million project with sidewalks and plazas to connect the City of Sweetwater with the university’s Modesto A. Maidque Campus (MMC).
This was MCM’s first design-build project with FIGG, described in a news release as an award-winning Tallahassee-based firm. FIGG has designed bridges throughout the U.S. including the Leonard P. Zakim Bunker Hill Bridge in Boston and the Sunshine Skyway Bridge in Tampa Bay.
Both FIGG and MCM expressed condolences for the victims and say they are cooperating with the investigation, but not much more, at least in public.
But what caused the bridge to fail?
The Miami Herald has published an extensive investigative report, starting with these questions:
- Did it crack when it was lifted into place?
- Was it a snapping steel support that did it in?
- Or was it a fatally flawed design from the start?
- And what was the doomed construction crew member doing when the bridge buckled under him?
Each of these questions could have different answers, and the newspaper reported about speculations and varying interpretations within engineering forums. But the details of what really happened are stored at the NTSB and it may take a year or more for the investigators to release their findings.
In the most recent news release March 21, the federal agency said: “The next update on the progress of this investigation will likely be the preliminary report. Preliminary reports are generally completed within a few weeks following completion of field work. Preliminary reports do not contain analysis and do not address probable cause.”
In other words, NTSB will likely be totally silent for several weeks, and then will decline to answer (at least for now) the questions about why the tragedy occurred.
In its March public statement, the NTSB said that significant developments in the investigation include:
- Investigators secured a contract to have a company remove components from the bridge that it believes warrant additional examination and testing. These components include sections of the floor, the canopy, a vertical member and a diagonal member; all from the north end of the structure. These components were in the area of where the failure occurred. “In addition to these components, we obtained additional core samples from this area to supplement the core samples we obtained earlier,” the NTSB statement said.
- Shipping the core samples along with some recovered rebar and tensioning rods to the Turner Fairbank Highway Research Center, in McLean, VA, for testing and evaluation.
- The investigative team has obtained an exemplar tensioning rod and hydraulic unit used by the construction crew to make tension adjustments to the tensioning rods. These items are also being shipped to the Virginia research center for evaluation and testing.
- The larger bridge components the investigative team is removing are being stored at a secured Florida Department of Transportation facility, under the control of the NTSB. The additional examinations and forensic deconstruction of these components will occur there.
The investigative team has confirmed that workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge collapsed. They had done this same work earlier at the south end, moved to the north side, and had adjusted one rod. They were working on the second rod when the span failed and collapsed.
The roadway was not closed while this work was being performed.
NTSB says ongoing work includes:
- Removal of the post-tensioning device to a temporary storage area and preparing it for shipment;
- Preliminary comparison of bridge schematics to measurements obtained during the investigators’ examination of the collapsed structure; and
- Interviews with first responders.
The NTSB said that “while segments of the bridge are being transported to and stored at an FDOT facility, there are no plans to reconstruct the bridge as part of the NTSB investigation into why the bridge collapsed. The nature of the structure and the way it failed make reconstruction impractical.”
There have been unofficial speculations about whether the design was properly evaluated before construction began, and whether the contractor had received briefings on how to safely build the structure.
“Outside expert speculation has moved beyond just potential construction error to focus increasingly on possible design flaws that might have made the bridge structurally vulnerable,” the Miami Herald reported.
“I would say they were pushing the envelope,” Nel Hawkins, an emeritus engineering professor at the University of Illinois who specializes in concrete construction was quoted as saying. “The question is, to what extent had the new concepts in this been validated through testing prior to actually putting it in place?”
The Herald reported that the “admittedly speculative consensus has coalesced around a view of the FIU project as a novel design with a high ‘wow’ factor, but also hidden structural risks and vulnerabilities that were probably compounded by a last-minute design change, all brought to a catastrophic conclusion by engineering and construction miscalculations.”
But it will likely be many months – perhaps years – with presumably extensive litigation – before the story can truly come to a definitive conclusion.
The story touches close to the heart of FIU, with nationally recognized programs in engineering and construction management.
The university’s Moss School of Construction, Infrastructure and Sustainability attracts students from across the U.S. and internationally with its programs.
The school is “the preeminent center for advancement and dissemination of construction knowledge,” director Irtishad Ahmad says on the FIU website. “Our undergraduate students get hands on training and high class instructions in all areas of construction. Graduate students take courses in advanced topics in construction and get involved in research with the faculty members. Both groups enjoy excellent employment opportunities by being in South Florida – one of the busiest geographic regions in construction in the country.”