By: KDKA-TV News Staff
PITTSBURGH (KDKA) -- The Fern Hollow Bridge collapse began on the Squirrel Hill side - or west end - of the structure, according to the National Transportation Safety Board's initial report.
The NTSB's preliminary report was released Monday afternoon and includes more details on the investigation into the failure of the structure.
The full investigation into the collapse will include an extensive look at the surveillance video captured from inside the Port Authority bus that was on the bridge when it collapsed. The NTSB says they will convene a group of specialists to analyze all of the video.
The bus had seven cameras: one forward-facing camera, one right side aft facing camera, and five interior cameras.
Video was recovered from them all, the NTSB said.
"The initial assessment of the video data is consistent with the initial assessment of the bridge components," the initial report said.
The report also contains a detailed description of the structure.
"The bridge was an uncoated weathering steel, three-span, continuous rigid 'K' frame structure with two welded steel girders, welded steel floor beams, and rolled steel stringers. The ends of the structure rested on reinforced concrete caps on stone masonry abutments. Each girder was additionally supported by two inclined, welded steel frame legs, also made of uncoated weathering steel, which rested atop reinforced concrete thrust blocks. Although certain areas of the welded steel girders were identified as being fracture critical, no primary fractures were found in these areas."
The full investigation into the collapse is expected to be a lengthy process while the NTSB gathers evidence and completes the review process.
They are also expected to release safety recommendations to prevent future incidents like the Fern Hollow collapse.
The reports says:
"The NTSB is evaluating the design of the bridge, its condition at the time of the collapse, its maintenance and rehabilitation history, and its inspection and load rating history. As the investigation progresses, the NTSB plans to conduct forensic examination of several of the bridge's structural components. The recovery of evidence, including extraction and documentation, is expected to be a lengthy process. 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."
The Federal Highway Administration, PennDOT, Port Authority and the city are all assisting the NTSB in the full investigation.
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