The National Transportation Safety Board (NTSB) has determined that load and capacity calculation errors made by FIGG Bridge Engineers, Inc., are the probable cause of the fatal, March 15, 2018, Florida International University pedestrian bridge collapse in Miami.
Review company not qualified
Contributing to the collapse was an inadequate peer review by Louis Berger, the independent consultant hired to verify the bridge's integrity and design by FIGG. According to the NTSB, Louis Berger failed to detect FIGG’s calculation errors in its design of the main span truss member 11/12 nodal region and connection to the bridge deck. The FIGG engineer of record’s failure to identify the significance of structural cracking observed in this node before the collapse, and failure to obtain an independent peer review of the remedial plan to address the cracking, further contributed to the collapse.
The NTSB determined that Louis Berger was not qualified by the Florida Department of Transportation to conduct an independent peer review.
Fatalities and injuries
Six people died and 10 others were injured when the partially constructed FIU pedestrian bridge catastrophically failed, sending the 174-foot-long, 950-ton, bridge span onto SW 8th Street 18.5 feet below, crushing eight vehicles that were under the bridge. Six of the eight lanes of the roadway traveling under the bridge were open at the time of the collapse.
The failure of FIGG, MCM, Bolton Perez and Associates Consulting Engineers, FIU and the Florida Department of Transportation to cease bridge work and close SW 8th Street to protect public safety contributed to the severity of the collapse outcome, said the NTSB during the meeting.
“Errors in bridge design, inadequate peer review and poor engineering judgment led to the collapse of this bridge,” said NTSB Chairman Robert Sumwalt. “The failure of all concerned parties, to recognize and take action on the threat to public safety presented by the significant observed bridge structure distress prior to the collapse, led to the tragic loss of life in this preventable accident.”
Cracks in the structure
Through its investigation the NTSB made 30 findings including:
- Concrete and steel materials used during construction of the bridge were not a factor in its collapse and the hydraulic jack used to post-tension the steel rods in member 11 was operating as expected at the time of the collapse.
- The restressing of member 11 was a manipulation of loads to address structural cracking of unknown origination constituting a change to the FIGG design and should have been independently reviewed by a professional engineer before being implemented.
- FIGG’s bridge design was nonredundant because it provided only a singular load path.
- FIGG’s construction plans inconsistently identified when intentionally roughened surfaces were needed to fulfill assumptions of the bridge design.
- Even if the cold joint surface of nodal region 11/12 had been roughened to a 0.25-inch amplitude, node 11/12 would not have had sufficient capacity to counteract the demand load for interface shear – and the bridge would still have been under-designed and could have failed.
- The rate of premature concrete distress was clear evidence the structure was progressing toward failure and should have alerted FIGG and MCM to the origin of the distress.
- Florida Department of Transportation should have verified Louis Berger’s qualifications as an independent peer review firm as part of FDOT’s oversight of local agency program projects.
Based on its investigation of the bridge collapse, the NTSB issued 11 safety recommendations in total, with one issued to the Federal Highway Administration, five issued to the Florida Department of Transportation, three issued to the American Association of State Highway and Transportation Officials, and two issued to FIGG Bridge Engineers, Inc.
An abstract of the NTSB’s report containing the probable cause, findings and recommendations from its investigation of the FIU pedestrian bridge collapse is available online at https://go.usa.gov/xp3uB. The full final report will publish in the next few weeks.