PROJECT OVERVIEW
When the Fern Follow Bridge in Pittsburgh’s Frick Park
collapsed on January 28, 2022, four people sustained non-life-threatening
injuries. Had the bridge collapsed an
hour later, during peak commuter time, it could have been a different story.
Following the collapse, an emergency project team was
assembled and given the green light to start working on the rebuild
immediately. With conventional methods,
replacing a bridge this size typically would have taken three to four years,
plus the time required to redesign the bridge, plan the bridge construction,
obtain approvals, prepare the site, and install substructure elements. Using prestressed concrete beams for the
bridge superstructure assisted the Fern Hollow Bridge completion in less than a
year.
TEAM OVERCOMES
CHALLENGES
One obstacle was related to the design process. “The primary challenge in the design
phase was the accelerated time factor,” says Greg Gorman, president and COO of
PennStress. “The team performed the
incredible feat of redesigning the original 450 ft span steel K-frame structure
to a three-span prestressed concrete beam structure in a few months. Highly expedited shop drawing preparation by
PennStress and subsequent review and approval by the project team were a
success as well.” Production, which was
also critical, did not pose significant difficulties. “We had no out-of-the ordinary challenges in
the production activity for these twenty-one large, prestressed beams since we
are accustomed to producing beams of this size,” notes Gorman.
Delivery turned out to be the greatest hurdle for PennStress
in the process of this bridge replacement. “We worked with the project team immediately after our award to
determine the safest feasible delivery routes for the beams through the city to
the jobsite,” he says. “When it came
time to deliver the super-load beams, the city of Pittsburgh operational
managers, the police, and the motorcycle police did an excellent job of guiding
us safely through the city to the site.”
PRECAST SOLUTION
The project team took a big step in rebuilding the bridge,
opting to replace the old steel bridge with prestressed concrete beams from
PennStress. This decision was made
because of precast concrete’s exceptional strength and flexibility, which
fueled the project’s extraordinary construction rate. Using precast concrete helped the project
team meet critical high-performance measures while reducing the need for other
materials and human resources. Because
precast concrete is fabricated off-site in a factory-controlled environment,
PennStress was able to guarantee consistent, accurate pours every time and
deliver structural components to the jobsite on a just-in-time basis.
Read the full Project Spotlight in the 2023 May-June, Bridges issue of the PCI Journal |