The failure of the city of Pittsburgh to act on repeated maintenance and repair recommendations for the Fern Hollow Bridge for more than a decade was the likely cause of the structure’s dramatic collapse in 2022, the National Transportation Safety Board (NTSB) on February 21, 2024. , meeting. The city owns the bridge.
The NTSB cited poor annual inspections and insufficient oversight by the Pennsylvania Department of Transportation and other agencies as contributing factors to the incident.
The determination was based on a 25-month investigation following the Jan. 28, 2022, collapse of the weathered 52-year-old, 447-foot-long, three-span steel bridge that sent a transit bus and several others . vehicles falling approximately 100 feet into a ravine. There were no fatalities from the incident, but nine people were injured.
The NTSB reviewed evidence that included field studies of the collapse site, materials testing and finite element analysis, interviews with city and state agency personnel and contract inspectors, and a review of design documentation , manufacturing and maintenance as well as transit bus videos. cameras on board.
Inspectors located the failure at a cross-tie plate on the southwest portion of the structure, which had significant corrosion and loss of section due to water and salt runoff from perpetual drains obstructed from the bridge. This prevented the formation of a protective patina around the area.
The board said the city’s failure to respond to inspection reports since 2005 documenting increasing deterioration ultimately caused the leg to lose sufficient structural capacity to support the bridge’s load at the time of the collapse.
The NTSB also failed annual inspection processes, conducted by three separate consulting firms that PennDOT hired and managed on behalf of the city.
In addition to procedural deficiencies, such as insufficient cleaning of corrosion prior to measuring loss of section, “contractors did not properly identify the bridge legs, including the transverse tie plates, as tension members d “non-redundant steel of critical members for fracture,” the NTSB said. found, a determination that would have triggered deeper practical inspections.
“Had the City of Pittsburgh taken adequate steps to repair or strengthen the loss of the fracture-critical bridge leg component section,” the NTSB added, “the collapse of the Fern Hollow Bridge could have to have been avoided”.
PennDOT’s insufficient oversight of the city’s bridge inspection program contributed to the bridge’s continued deterioration, the Board said. Of note were the inaccurate load calculations that did not directly account for the localized effect of section loss, nor had the engineers used the correct K-factor to estimate the axial load capacity.
The city’s poor paving records also failed to document that the bridge’s asphalt wearing surface at the time of the collapse was roughly twice the 3-inch design thickness.
“Had the load capacity calculation properly taken these factors into account, the result would have required the bridge to be closed,” the board said.
NTSB Chair Jennifer Homendy told reporters after the board meeting that while responsibility for the bridge’s failed maintenance rests squarely with the city of Pittsburgh, action could have been taken at any level to address these issues.
“It was failure after failure,” Homendy said.
The board noted that the City of Pittsburgh and PennDOT separately have already taken steps that “have the potential to address the deficiencies found in this investigation,” but stressed that the state agency should take the lead in time to evaluate the effectiveness of the measure to improve the safety of the bridge.
Recommendations were also issued to the Federal Highway Administration and the American Association of State Authorities and Transportation Officials to address safety issues identified in the investigation, including updating inspection guides and inspection programs. training and refinement of bridge load classification practices.
The NTSB also reiterated its May 2023 recommendation that federal and state transportation authorities take immediate action to resolve outstanding maintenance issues for uncoated weathering steel plate structures similar to the Fern Bridge Hollow.
The NTSB’s final report on the collapse will be released in several weeks.
