PITTSBURGH — The National Transportation Safety Board's preliminary report Monday on the Jan. 28 Fern Hollow Bridge collapse indicates the bridge began falling from the Squirrel Hill side of the structure, but it doesn't offer any reason why.
The report, which the agency normally releases about 10 days after a major incident, indicates the agency expects to spend more time at the Frick Park ravine where the bridge debris fell. Its full investigation could take as long as 18 months.
The investigation team, lead by NTSB Chairwoman Jennifer Homendy, has been reviewing the scene since the collapse happened. Construction crews over the weekend began lifting heavy pieces of debris so investigators could look under it for evidence.
The collapse, which occurred about 6:40 a.m., took a Port Authority bus and five other vehicles into the ravine. Ten people were injured.
"Initial assessment of bridge components indicates that the collapse initiated at the west end of the structure," the report said. "Further examination will be performed as debris from the bridge is removed and unobstructed access becomes available...
"The recovery of evidence, including extraction and documentation, is expected to be a lengthy process."
The bridge has been listed in poor condition since 2011, with inspectors raising particular concerns about the condition of steel supports. Cables were installed on the west end to bolster the supports.
The initial investigation found no fractures of bridge beams, the report said.
"Although certain areas of the welded steel girders were identified as being fracture critical, no primary fractures were found in these areas," the report said.
Under federal regulations, a fracture critical member is a "steel member in tension, or with a tension element, whose failure would probably cause a portion of or the entire bridge to collapse."
The bridge, opened in 1973, was considered a K-frame design. That design has the bridge resting on supports set in the ground, but it has no second support if they fail.
The state Department of Transportation has ordered five other bridges across the state with a similar design to be reviewed.
That design will be part of the federal investigation.
"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," the report said. "As the investigation progresses, the NTSB plans to conduct forensic examination of several of the bridge's structural components."
The bridge, owned by Pittsburgh, had been rated in poor condition since 2011, first due to deterioration with its superstructure and later additional problems with its deck. Its inspection schedule was ramped up from every other year to yearly after 2014, but it wasn't scheduled for major repairs until at least 2027.
City officials say they aren't allowed to release inspection reports or discuss its maintenance history because of the federal investigation.
The bridge collapsed slowly in sections, which prevented vehicles from being thrown off violently or crushed in the rubble. The bus was trapped from the rear by another slab of the bridge when the piece it was on fell at about a 45-degree angle, preventing it from falling backwards.
Emergency crews were able to get the driver and two passengers off the bus using a ladder.
The Federal Highway Administration has awarded the state an emergency grant of $25.3 million to design and build a new bridge. PennDOT is leading that effort and has hired HDR Inc. to design the new structure and Swank Construction Co. to build it. They received no-bid contracts for the work so the contractor can build sections as they are designed.
The 497-foot bridge carried Forbes Avenue from Squirrel Hill to Point Breeze in Pittsburgh's East End. President Joe Biden, who was scheduled to be in the Pittsburgh area that day to tout his infrastructure program, visited the scene to lend emphasis to the need for improvements.
