NTSB Requests Weathering Steel Bridge Action
On Thursday (May 18), the National Transportation Safety Board (NTSB) announced new recommended actions for bridge maintenance, following the ongoing investigation of the 2022 Fern Hollow Bridge collapse in Pittsburgh. The recommendations call for federal and state authorities to review inspection reports and to identify incomplete follow-up actions that need to be resolved for bridges made of uncoated weathering steel.
Uncoated weathering steel requires periods of dryness for a protective oxide coating to form. This coating or patina, usually resists corrosion.
Investigators report that they have found evidence of corrosion, deterioration and section loss on all four of the bridge’s legs as a result of water and debris accumulation. Debris, dirt and leaves were all reportedly blocking the bridge’s drainage systems, resulting in water flowing to the wrong areas and preventing a protective patina from forming.
Investigators have also stated that past inspections on the bridge, performed by the Pennsylvania Department of Transportation, identified issues with drainage but failed to perform regular maintenance.
NTSB urges action on bridges nationwide as part of ongoing investigation into 2022 Pittsburgh bridge collapse:— NTSB Newsroom (@NTSB_Newsroom) May 18, 2023
News release: https://t.co/lIq6KaAnDq
Interim report and early recommendation: https://t.co/GKSC2wMG2f pic.twitter.com/VpWTfGmqcu
Consequently, the NTSB has asked the Federal Highway Administration “to develop a process for bridge owners nationwide to perform necessary follow-up actions on bridges with uncoated weathering steel components.”
Along with the early recommendation, the NTSB also released new documents with photos and 3D-laser scans of the deterioration of all four bridge legs.
“Safe, reliable infrastructure is a top priority of the (Gov. Josh) Shapiro administration, and we are committed to ensuring Pennsylvanians and all motorists can travel across the Commonwealth safely,” PennDOT Spokeswoman Alexis Campbell said in an interview.
“To that end, PennDOT remains proactive in its review, analysis and maintenance of its bridges.”
Bridge Collapse Background
On Jan. 28, 2022, the Allegheny County Police Department was notified about a partial bridge collapse over Frick Park. Emergency crews arrived at the Forbes Avenue Bridge, also referred to as the Fern Hollow Bridge, around Forbes and Braddock avenues.
Initial reports indicated that an articulated Port Authority bus and four passenger vehicles were on the bridge at the time of the collapse, along with a fifth passenger vehicle that drove off the east bridge abutment following the collapse. First responder crews rappelled 100 to 150 feet to reach victims, while others formed a “human chain” to rescue people from the bus.
A preliminary NTSB investigation reported that 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, with each girder additionally supported by two inclined, welded and uncoated weathering steel frame legs on concrete thrust blocks.
According to the release, certain areas of the welded steel girders were identified as being fracture critical, but no primary fractures were found in those areas. Initial assessment indicates the collapse began at the west end of the bridge.
In May of that year, the NTSB provided an update on the recovery of structural components and tests currently being conducted to evaluated materials used when constructing the bridge, as well as a review of new footage recovered from a transit bus camera system.
Investigators reviewed video footage from the time of the collapse from two of the cameras on a Port Authority transit bus. The cameras, one forward-facing and one rear-facing the curbside, were determined to have “investigative value” with frames depicting events of interest.
The first frame, from the forward-facing camera, reportedly shows the bridge deck separating at the east expansion joint. The second frame, from the curbside camera, reportedly shows that, at nearly the same time, the west end of the bridge had already fallen off the west abutment.
Additionally, while the preliminary report listed ten vehicle occupants as being injured during the bridge collapse, further investigation has confirmed a total of nine occupants in six vehicles, including the Port Authority transit bus. Of the injuries, two vehicle occupants sustained serious injuries, two injuries were minor, four were uninjured and the injury status of one is unknown.
That same month, a newly released inspection document revealed that the Fern Hollow Bridge had “major decay” prior to its collapse, including exposed rebar, corrosion, holes in the steel cross-beams and spalling in the bridge deck.
In December, officials opened the new Fern Hollow Bridge, after the construction of the replacement structure was completed less than a year after the original bridge’s collapse in January. The bridge is currently open to a single-lane of bi-direction traffic.
The opening, however, arrived just as the new Comprehensive Bridge Asset Management Program released a report, highlighting structural issues with dozens of bridges maintained by the city that should be addressed within the next six months. The full report can be viewed here.
Local engineering firm WSP, which was unanimously approved a $1.5 million, two-year contract to inspect and evaluate all city-owned bridges in July, conducted inspection reviews of 147 bridges.