Project Overview
In the early morning hours on January 28, 2022, Fern Hollow Bridge collapsed in Pittsburgh, Pa., sending several vehicles and a Port Authority bus into a ravine below. Thankfully, the collapse only resulted in a handful of injuries and no fatalities. However, with the route carrying more than 20,000 vehicles per day, an emergency replacement was needed to restore this critical passage for commuters. Officials with the Pennsylvania Department of Transportation (PennDOT) chose precast concrete for the new bridge, specifying a three-span structure that would use 21 prestressed concrete 33/95.5 PA bulb-tee beams, each weighing more than 100 tons and measuring roughly 152 ft in length.
Fast, Durable, and Safe
Owing to the severity of the situation and the pressing need to install a new bridge at the location, state officials approved an emergency proclamation that allowed PennDOT and the City of Pittsburgh to leverage all available powers, resources, and personnel necessary to rectify the situation. A progressive design-build delivery process was selected, which, when combined with the decision to use precast concrete, accelerated the project schedule from four to five years to just under one year. As a result, motorists could quickly resume using the route made possible by Fern Hollow Bridge, avoiding a congested detour that had added approximately 20 minutes to commute times.
Many aspects of the design of the new bridge, including the existing bridge’s location, right-of-way limitations, traffic volume, and environmental and historical impact, were carefully evaluated. Key objectives included reassuring the public that the bridge would be safe and providing a structure that would reduce maintenance while providing a design to exceed the American Association of State Highway and Transportation Officials’ minimum 75-year design life. The high-quality prestressed beams selected for the project helped address all these considerations.
PennStress of Roaring Spring, Pa., manufactured the beams efficiently, readying them for their intended use within six months of the original steel bridge’s collapse. This time frame was well ahead of those for other potential superstructure options, and using an off-site fabrication process simplified concurrent work taking place at the project site.
Because they prestressed beams were fabricated in a controlled environment and have protective coatings and material requirements that meet PennDOT’s design manual and specifications, the prestressed beams boast a service life of more than 100 years. Thus, the new, 460-ft-long Fern Hollow Bridge will provide a secure route for commuters to navigate the busy Pittsburgh suburbs for years to come.
Read the full Project Spotlight in the 2023 May-June, Bridges issue of the PCI Journal
Mason Nichols is a Grand Rapids, Mich.-based writer and editor who has covered the precast concrete industry since 2013. |