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The NTSB has released a preliminary report on the March 15 collapse of the FIU pedestrian bridge that killed six
There will be months more of investigation before NTSB releases a final report
More than two months after the FIU bridge collapsed onto Southwest 8th Street, the National Transportation Safety Board is out with a preliminary report that sheds little or no new light on its causes.
The report does confirm what the NBC 6 Investigators revealed the day after the March 15 collapse – that at the moment of collapse, a crew was re-tensioning the steel bars the ran through a diagonal truss on the north end of the span, the area where the collapse originated.
Those bars – called post-tension rods – were de-stressed after the bridge was set into place on March 10, as set out in the bridge design plans.
They were supposed to remain destressed.
But cracks in the concrete – reported by the chief bridge engineer to FDOT on March 13 – had to be repaired, the engineer said.
Two days later, the company that de-stressed the rods on Saturday was called back to re-stress them – something not called for in the original bridge design.
It was during that procedure that failure occurred.
The NTSB report included photographs taken on February 24 of cracks at the point where the diagonal truss being re-stressed on March 15 joined with the bridge deck.
Those cracks were detected after the removal of temporary shoring – used to support the structure as it was constructed on the roadside prior to it being lifted in place on March 10.
On February 6, smaller cracks were noted in a truss adjacent to the one that apparently failed and another on the south end of the bridge, according to records obtained by NBC 6 from FIU. A week earlier, on January 29 and 30, the post-tension rods in the northern- and southernmost trusses were stressed – according to plan — as the bridge section rested on its shoring, according to the memo from bridge inspector Bolton Perez & Associates.
“The intent is to monitor these cracks after the bridge is fully tensioned and the main span is at the final location,” states the memo to the design- build team, Munilla-MCM and FIGG Bridge Engineers.
There will be months more of investigation before NTSB releases a final report.
“In the next month, the NTSB will be conducting additional forensic examination of several bridge structural components and destructive testing of multiple core and steel samples,” report states. “All aspects of the collapse remain under investigation while the NTSB determines the probable cause, with the intent of issuing safety recommendations to prevent similar events.”