Engineering-News-Record-Southeast by Scott Judy and Richard Korman May 24, 2018
A final determination of the deadly accident's cause could take 24 months
The National Transportation Safety Boardâ€™s preliminary report on the fatal collapse in March of a pedestrian bridge at Florida International University in Sweetwater focuses attention on the widely discussed pre-collapse cracking in the main span. The report also confirms accounts about what the construction crew working on the bridge was doing before the structure fell.
But the report contains no definitive explanation of what occurred and months and possibly years more will be needed to determine the probable cause of the failure, which killed five motorists and one project worker.
Issued May 23, the NTSB report states that while the board â€œis evaluating the emergence of cracksâ€ in diagonal members located at both ends of the bridge, it is also studying â€œthe propagation of cracksâ€ near diagonal member 11, located at the structureâ€™s north end.
A video of the collapse appears to show the failure starting at that part of the concrete truss bridge's main span.
Seven vehicles beneath the 174-ft-long bridge were occupied at the time of the collapse early in the afternoon of March 15. The partially constructed pedestrian bridge was being built by a design-build joint venture called MCM-FIGG, consisting of contractor MCM Construction and FIGG Engineers, both based in Florida.
Following the design plan, construction crews five days prior to the collapse were "de-tensioned the bridge diagonal members on the north and south ends of the bridge," the report states. On March 15, the day of the accident, a construction crew was busy "re-tensioning the number 11 diagonal member connecting the canopy and the deck at the north end of the bridge,â€ states the report.
Photo 2: A second photo of a crack in the region of diagonal 11 of the failed Florida International University pedestrian bridge. The cracks are a focus of federal investigators.
Much speculation about the cracks has been published.
The project teamâ€™s knowledge of pre-collapse cracking in the bridge span was first reported on March 16, when the Florida Dept. of Transportation (FDOT) released the transcript of a voicemail it had received from the bridge projectâ€™s lead engineer prior to the collapse.