Accelerated bridge construction (ABC) is a powerful tool for rapidly upgrading our nation’s bridge infrastructure using high-performance precast concrete solutions. The Interstate 78 (I-78) Bridge Underclearance Project in Berks County, Pa., is a great example of how ABC delivers tremendous benefits for owners and the community.
Pennsylvania Department of Transportation (PennDOT) Engineering District 5 chose the ABC technique to build six precast concrete structures with spans ranging from 10 3ft to 133 ft over two construction seasons. The decision was driven largely by community input, says Brian Brawand, project manager and senior associate for Alfred Benesch & Company. “During public outreach, community members and bridge users consistently indicated a preference for these bridges to be constructed under brief roadway closures with ABC techniques, rather than with longer-duration conventional staged construction.”
It was a bold decision for PennDOT, which had minimal experience with this construction technique. “At the time of design and construction, ABC projects were atypical across the United States—and even more so in Pennsylvania, where relatively few of them had been completed,” Brawand says.
And while most ABC projects include the replacement of one particular bridge, the I-78 Bridge Underclearance Project had to deliver six bridges in sequential order. It was also was the first Pennsylvania ABC project to incorporate tall cantilevered abutments. “These project characteristics resulted in a challenging project throughout both the design and construction phases of the project,” he says.
But the project team was up the challenge.
45 days per bridge
The updated structures were composed of single-span prestressed concrete bulb-tee bridge beams along with precast concrete substructures accented by a stained, stone-faced formliner. The full-depth precast concrete deck panel pieces were typically 8 in. thick and less than 14 ft wide to facilitate transportation to the project site.
Because the six bridges had significantly different bridge widths, some used precast concrete deck panel components that extended across the full bridge width, while others used two or three precast concrete deck panel components.
The precast concrete detailing for all six structures was completed by PennStress, which used TEKLA 3D modeling software so that no two pieces were the same structural layout or appearance. TEKLA virtually eliminated production material conflicts, enhanced the accuracy of the splice sleeve layouts, and even allowed for a visual representation of the stone-faced formliner layout between pieces to provide the desired look, Brawand says.
To customize the look and feel of each bridge, the precast producer used a random block stone architectural finish on the outside face of the barriers and front face of the abutment and wing wall stems. Five different-colored stains were also applied, providing a natural stone appearance. “These aesthetic features provide a simple, consistent, and visually appealing appearance at the six consecutive overhead bridges along an 8-mile stretch of Interstate78.”
To minimize disruption to traffic, each bridge was individually detoured for a specific duration to allow the demolition and reconstruction to take place, with much of the work taking place at night. Segments of the work included short-term, scheduled interruptions to the traffic flow on I-78, a major interstate in the mid-Atlantic region. This plan “reduced the average construction duration for each structure from one year to just 45 days,” Brawand says. That meant all six bridges could be completed in in two construction seasons, minimizing the project’s social and economic impact on local businesses.
“It was an honor to be a part of the project team for this successful project, working together to achieve these goals and seeing the project progress from preliminary design through construction,” Brawand adds. “Assisting PennDOT District 5 in showcasing the project and their use of innovative design and construction technologies has been a pleasure.”