The Harrison Avenue Bridge has been a fixture in Scranton, Pennsylvania since 1922, when a citizen group’s campaigned for its construction. Library of Congress/HAER
Design work continues on replacing the historically important Harrison Avenue Bridge, in Scranton, Pennsylvania, which crosses the formidable Roaring Brook gorge.
March 5, 2013—Final design work is under way on a replacement for the Harrison Avenue Bridge, a 90-year-old crossing in Pennsylvania considered the “gateway to Scranton.” The elegant, open-spandrel ribbed arch bridge has been a fixture in the city since 1922, when a group of citizens campaigned for its construction.
With a length of 407 ft, the three-span concrete structure was designed by the noted engineer Abraham Burton Cohen and is listed in the National Register of Historic Places. It spans Roaring Brook gorge, a deep, inaccessible ravine flanked by the Central Scranton Expressway and operating rail lines, which the bridge also crosses. More than 15,000 motorists a day use the bridge to travel between the southern and eastern parts of Scranton.
Water draining through joints, cracks, and other permeable areas of its deck has taken a toll, and the Harrison Avenue Bridge needs a number of repairs. Advanced deterioration prompted the Pennsylvania Department of Transportation (PennDOT) to lower the bridge’s weight limit to 15 tons and to begin work on a replacement.
PennDOT hired Dewberry, of Fairfax, Virginia, to design a new bridge for the crucial crossing, placing a strong emphasis on the aesthetic elements of the project. As if replacing an iconic local bridge weren’t enough of a challenge, there is no access into the steep ravine for construction equipment, and the geotechnical conditions at the site are less than ideal in that large rocks are exposed or located near the surface.
The new bridge will be 49 ft wide, including two lanes for traffic and
a 7 ft shoulder and a 5 ft sidewalk on each side. Courtesy of
Dewberry and PennDOT
“Because the project involves replacement of a historical bridge at a prominent location, the architectural and aesthetic characteristics of the new bridge are significant considerations,” said George Parish, a design engineer on the project for Dewberry, in written comments to Civil Engineering online. “Several design features are intended to be reminiscent of the original bridge and the historic characteristics of the surrounding area.”
The design team considered a concrete or steel arch replacement, as well as a structure that would have spliced girders of prestressed concrete. The physical characteristics of the site and the steep gorge, however, would have made these options difficult to construct and prohibitively expensive.
Instead, the new bridge will be a three-span steel girder structure, the webs having multiple haunches to give an arch appearance. The center span will be 205 ft long, and the two end spans will each have a length of 130 ft. The end-span girders will be 54 in. deep at their centers, increasing to 102 in. at the piers. The center span will be 72 in. deep, increasing to 102 in. at the piers. The 49 ft wide bridge will have two lanes for traffic, along with a 7 ft shoulder and a 5 ft sidewalk on each side.
Two massive reinforced-concrete piers—one extending 50 ft and the other 70 ft into the gorge—will each comprise three 7 ft diameter columns. Spread footings, micropiles, and drilled shafts are all being investigated as foundations for the piers; constructability will determine the final decision.
“There is no viable route to the bottom of the gorge for construction equipment,” Parish explained. “The anticipated methods for constructing the piers will require large cranes working from the upper sides of the gorge. The cranes will need to be situated as close as possible to the piers. Temporary crane platforms constructed at the rim of the gorge are anticipated.”
The new alignment will require changes to Duffy Park, which will be
enlarged and enhanced with new facilities as part of the project.
Period lighting and other aesthetic elements will be continued in
the park. Courtesy of Dewberry and PennDOT
The pier caps also will be haunched between the columns to evoke the arches of the existing bridge. “Decorative pillars, reminiscent of those found on the original Harrison Avenue Bridge, will be constructed to rise from the pier cap to above the travel-way,” Parish said.
In addition to those pillars, the design team has specified architectural surface treatments on the faces of abutments and wing walls. A solid barrier with formed reliefs and recesses will evoke the original bridge’s concrete barriers. The project will also include decorative street lighting on the bridge and the approach roadways.
The new bridge will be constructed slightly west of the existing crossing, providing an improved intersection with connecting streets. The proposed new alignment will also enable PennDOT to build the new bridge while the existing structure remains in service.
The new alignment will require the relocation and expansion of Duffy Park, on the west side of the bridge. The design calls for the enhancement of the park as part of the process and the addition of walking paths, benches, irrigation systems, and dedicated parking. The decorative period-style lighting and other elements of the bridge will be continued into the park to provide continuity.
The project is in the early stages of its final design, and construction is expected to begin next year. The new bridge should be completed by the fall of 2015 at a projected cost of approximately $12 million.