What to Know
The FIU bridge collapse on Thursday killed six people.
Authorities are investigating the cause of the deadly bridge collapse.
The NTSB federal agency is focusing its investigation on one part of the bridge.
It emerges on dashcam video about one-fifteenth of a second before the FIU pedestrian bridge collapses – a puff of some kind and what appears to be a protrusion from the deck level of the north side of the structure.
And then it all comes tumbling down.
Whether it’s concrete or steel or something else, the National Transportation Safety Board announced Wednesday it is focusing on the area where that anomaly is seen -- where the last diagonal truss meets the deck and the vertical support beam on the north end of the span.
They are taking for examination and testing “sections of the floor, the canopy, a vertical member and a diagonal member … from the north end of the structure … in the area of where the failure occurred,” the agency said.
Also being shipped to the Turner Fairbank Highway Research Center in McLean, VA: the actual tension rods and hydraulic equipment found in the rubble as well as items nearly identical to those being used in order to test them. The equipment was being used to adjust the tension in rods that passed through the northernmost diagonal truss at the time of the collapse.
Earlier, the subcontractor had done the post-tensioning adjustments to two rods that pass through the diagonal truss at the southern end.
They moved to the north end, adjusted one rod there and were working on the second rod in that truss when the span failed and collapsed, NTSB said.
The original design called for those stress adjustments to be completed before SW 8th Street was reopened to traffic early on the morning of Monday March 12. The road was closed that weekend so that the span could be moved into place.
While the design called for tension to be added to the trusses on the north and south ends during that transport, the force was supposed to be reduced to zero after the bridge was put into place – and it was, according to one source close to the project.
But then cracking was observed – something chief engineer W. Denney Pate of FIGG Engineering reported on Tuesday to Tom Andres, a Florida Department of Transportation state structures design engineer. Andres did not get the voicemail until the day after the collapse.
But an FDOT consultant helping oversee the project was aware of the problem and how Pate was proposing to address it, according to FIU.
But no one called for the road to be closed again when the stress adjustments were being done, with Pate saying he determined the work would not create a safety issue.
Six people died in the collapse including an employee of subcontractor VSL, the firm doing the post-tensioning work.