An historic bridge in Pennsylvania is transformed into a safe structure for vehicles and a landmark the community could be proud of.
By Bridget McCrea
Replacing a 104-year-old dual, brick-arch bridge in a way that not only makes it functional again, but also preserves its historical qualities, is a tall order. Ready to meet the challenge head-on, a team of engineers, contractors and precast concrete manufacturers transformed a historic bridge in Chester County, Pa., into a structure safe for vehicles that the surrounding community could be proud of for many years to come.
Down in history
The project began in 2004, when the Pennsylvania Department of Transportation (PennDOT) declared the bridge unsafe and closed it. According to Rex Mackey, senior civil engineer and manager with PennDOT in King of Prussia, Pa., the bridge had collapsed in certain spots. Extensive repairs had been performed on the bridge at intervals throughout its life, but its condition slowly deteriorated. Vehicle weight limits were posted at 15 tons in early 2001, and the structure had to be completely closed to traffic in February 2003. “A chunk of the spandrel wall fell out, and there was a large hole up through to the pavement, making it unsafe for travel,” says Mackey.
That posed a problem for the surrounding community, which relied on the historic structure for traffic flow. The fact that two other bridges in the area were also closed only compounded the problem, according to Mackey, who says quick response of emergency vehicles was of particular concern. While the bridge is located in a rural setting, the surrounding region has substantial residential and commercial developments. The road carried by this bridge is an important urban collector, so closure of the bridge shifted commuter traffic onto a lengthy 11-mile detour using the closest available collector roads and onto local roads not meant to carry significant volumes of traffic.
“There were certain areas in the surrounding townships where those emergency responders couldn’t get to without using a lengthy detour,” says Mackey. “Getting this bridge replaced could mean life or death for someone.” Re-establishing this vital link in the regional highway network was of great importance, so the state secretary of transportation issued an emergency declaration to have the bridge returned to service as soon as possible.
The bridge, which is eligible for the National Register of Historic Places for its “uncommon use of building material and structure type” consisted of two 25-foot-long arches spanning separate channels (the main creek channel and a flood relief channel). On each side of the roadway, 65-five-foot long stone masonry spandrel walls connect the two arches, while the stone masonry U-wing walls at each corner of the structure lengthened the bridge to 165 feet. The first challenge, Mackey says, was finding a way to accurately match the existing brick and stonemasonry arches, which dated back to 1901, in a way that would preserve the bridge’s historic qualities and maintain its status on the National Register of Historic Places. For help, PennDOT called on San Francisco-based national engineering firm URS Corp. John Meyers, a project manager in Pennsylvania, worked with a team of engineers to handle the bridge’s highway and structural design, and the environmental work.
“Right off the bat there was a question of whether we were going to be able to replace it at all due to its status,” recalls Meyers. “We went through the process of documenting the existing bridge and coordinating with the Pennsylvania Historic Museum Commission (PHMC), which decided that it wasn’t practical to try to save the existing bridge, and agreed on replacement instead.”
Both PHMC and local officials wanted the new bridge to fit the historic character of the existing structure. The bridge lies within the boundaries of a historic boarding school founded in 1799 by the Society of Friends, commonly known as Quakers. According to Meyers, the bridge itself was historically significant, but also a contributing resource to the boarding school and farm historic district.
“Thus, any modifications to the bridge would have to be in keeping with the historic setting of the 600-acre school facility,” says Meyers. “Upon further investigation, we realized there were proprietary precast concrete arch bridge systems available that could be used to mimic the appearance of the original structure, including the use of architectural form liners and color stains to provide the faux-finish look of brick and stone construction.”
Meyers says precast concrete was the right choice, based on the material’s flexibility, quick installation process and cost savings. Using a combination of form liners and color staining, precast manufacturer Terre Hill Concrete Products of Terre Hill, Pa., was able to re-create the appearance of the original brick and stone.
“We were automatically steered right to concrete, and then right to precast concrete due to cost savings and the ability to be constructed more quickly than with cast-in-place,” says Meyers, whose team selected products from CON/SPAN Bridge Systems, provided by BridgeTek to help mimic the look of the existing structure. “It was a natural fit,” Meyers said.
Nelson Martin, vice president of operations at Terre Hill Concrete Products, says choosing precast helped PennDOT get the bridge back in service as quickly as possible. Precast also provided flexibility, says Martin, and the ability to rework stone patterns and other intricate details on the fly. “If the stone pattern wasn’t correct, it was easy enough to remake it,” says Nelson. “With cast-in-place, you’re either stuck with it, or you have to take some type of remedial repair action to get it right.”
Wall panels, barrier caps, headwalls and two arches spanning 42 feet and 12 feet comprised the precast concrete portion of the project. The overall structure was just over 162 feet long, and included precast concrete spandrel walls between the arches and precast concrete U-wing walls at each corner of the bridge.
By providing a faux-brick finish to the arches and a faux-stone finish to the walls, the new structure had a similar appearance to the original structure, while modified openings beneath the bridge and the channel protection ensured that the new structure would perform much better hydraulically.
“We realized significant savings on the construction cost and duration over traditional cast-in-place concrete construction,” Meyers adds, “while still adhering to all the modern criteria of structural, roadway and hydraulic design and meeting the project’s need to fit within the location’s historic and natural setting.”
Getting the structure replaced in a short period of time and within the historical requirements wasn’t easy, says Rich Tate, Pennsylvania region manager with BridgeTek in Philadelphia. Key challenges included designing the precast retaining wall panels in one piece – from the foundation to the top of the parapet – while maintaining the parapet wall as part of the precast retaining wall panel; constructing a form liner finish on both sides of the parapet and retaining walls; and developing a precast concrete cap that was not only functional but also aesthetically pleasing.
With those challenges behind them, Tate says there were also environmental issues to overcome. A stream had to be diverted, for example, and Mother Nature didn’t exactly cooperate in the wintertime. Overall, he says the project went relatively smoothly and, in the end, “worked out perfectly.”
“The installation was done in stages and the finished product looks terrific,” Tate says. “PennDOT now has a maintenance-free precast structure that should last a very long time.”
Completed in February 2005, the new bridge now carries two full-width traffic lanes with shoulders and meets the safety standards of a modern roadway. Mackey says from start to finish, the project cost $938,000, including $402,000 for the precast components, and exceeded PennDOT’s expectations.
“It worked out much better than we thought it would,” says Mackey, who was especially impressed with how well the precast ashlar stone mimicked the bridge’s original field touch stone. “They almost magically hid the joints between the panels, making it a very attractive structure that fits well with its surroundings.”