The US National Transportation Safety Board (NTSB) has released a report saying the probable cause of the collapse of a pedestrian bridge at Florida International University was load and capacity calculation errors by project designer FIGG Bridge Engineers.
The accident occurred in March 2018, when a 174ft, 950-ton bridge fell 18 feet onto eight cars, killing six and injuring 10.
The NTSB says US infrastructure group Louis Berger’s "inadequate peer review" contributed to the collapse, as it failed to detect calculation errors made by FIGG in its design of the main span truss member 11/12 nodal region and connection to the bridge deck.
NTSB diagram shows diagonal member 11 and vertical member 12 (NTSB)
Louis Berger was not qualified by the Florida Department of Transportation to undertake an independent peer review.
FIGG’s engineer of record contributed to the collapse as it failed to identify the significance of structural cracking observed in this node before the collapse, and also failed to obtain an independent peer review of the remedial plan to address the cracking.
The NTSB also cited a failure to cease bridge work and close SW 8th Street to protect public safety by FIGG, MCM, Bolton, Perez and Associates Consulting Engineers, FIU and the Florida Department of Transportation, which contributed to the severity of the collapse.
The NTSB concluded that steel and concrete materials used in bridge construction were not a factor in its collapse, and a hydraulic jack used at the time of collapse was operating as expected.
Robert Sumwalt, the NTSB’s chairman, said: "Errors in bridge design, inadequate peer review and poor engineering judgment led to the collapse of this bridge.
"The failure of all concerned parties to recognise 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."
A synopsis of the NTSB’s report can be read here. A full and final report will be published in the coming weeks.
The NTSB released an earlier report into the collapse in November 2018, and FIGG Bridge Engineers were previously criticised by the US Department of Labour’s Occupational Safety and Health Administration in June 2019.
Top image: Aerial view of the accident site soon after the bridge collapsed (Miami-Dade Police aviation unit via Twitter)