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Report reveals cracks on collapsed Florida bridge

Florida bridge collapse pa 35554090 3to2

Images and the location of cracks found on the Florida International University bridge have been released by the board investigating its collapse.

The images were released as part of an interim report published by the National Transportation Safety Board (NTSB).

The report gave scant new details on the cause or circumstances around the collapse, but did say the ongoing investigation was looking into the “emergence of cracking” found in the end diagonals two days before. The significance of the cracking was dismissed at a meeting of the design team, contractor and the Florida Department of Transportation (FDOT) just three hours before it collapsed. At the time, the team concluded that the crack did not compromise the structural integrity of the bridge.

The 53m long, 862t concrete trussed bridge collapsed on to a live highway on 15 March this year killing six people. The bridge was under construction at the time with works to post tension steel bars in the north end diagonal being carried out when it collapsed.

Works to tension bars in the end diagonal member at the south end had already been successfully carried out.

“The NTSB is evaluating the emergence of cracks in the region of diagonal members 2 (south end of the bridge) and 11 (north end of bridge), and the propagation of cracks in the region of diagonal member 11,” it said.

 

Hwy18mh009 prelim fig3

Elevation view of the pedestrian bridge.
(Source: Bolton-Perez and Associates Consulting Engineers)

Hwy18mh009 prelim photograph 1

Photographic documentation of the crack in the region of bridge diagonal 11.
(Source: Bolton-Perez and Associates Consulting Engineers)

It also said it was evaluating the bridge design, the construction process, and the construction materials with “all aspects” of the collapse remained under investigation.

The board said over the next month, it would be conducting additional forensic examination of several bridge structural components and destructive testing of multiple core and steel samples. It said it hoped to determine the probable cause with the “intent of issuing safety recommendations to prevent similar events”.

The $14.2M (£10M), main span was built offline using a method being dubbed Accelerated Bridge Construction (ABC). It was moved into position by a rig in just six hours on Saturday 10 March.

The bridge was designed by Figg Bridge Engineers and was being built by Munilla Construction company (MCM). Barnhart Crane and Rigging operated the self-propelled modular transporters that placed the bridge on its permanent supports.

Structural engineering experts in the UK told New Civil Engineer an explosive failure of a key joint in the bridge’s concrete truss was likely to have triggered its collapse.

The report also released a list of companies which were helping with the inquiry including Munilla and Figg.

  • Federal Highway Administration (FHWA)
  • FHWA - Turner Fairbank Highway Research Center (TFHRC)
  • Occupational Health and Safety Administration (OSHA)
  • Department of Transportation Office of the Inspector General (OIG)
  • Florida Department of Transportation (FDOT)
  • Miami-Dade Police Department (MDPD)
  • Florida Highway Patrol (FHP)
  • Florida International University (FIU)
  • City of Sweetwater (CS)
  • FIGG Bridge Engineers, Inc. (FIGG)
  • Munilla Construction Management (MCM)
  • Structural Technologies, LLC (VSL)
  • Barnhart Crane & Rigging (BCR)

 

 

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