By Kevin Wilcox
The High Bridge, which predates the U.S. Civil War, underwent an extensive rehabilitation and now once again links Manhattan and the Bronx.
Custom-made bricks replaced damaged pavers on the recently reopened High Bridge. The historic handrails were refurbished and a cable-mesh safety fence was added. Courtesy of StreetFilms.org
June 16, 2015—The most recently opened bridge in New York City also holds the distinction of being the oldest. The High Bridge—completed 13 years before the start of the Civil War—recently reopened to pedestrian and bicycle traffic for the first time since the 1970s.
"We couldn't be more thrilled. We are hoping that the High Bridge becomes a destination," says Ellen Macnow, the capital project coordinator in the New York City Department of Parks & Recreation (NYC Parks), who likens the structure to the popular High Line Park—but with the added wrinkle of history.
By any definition the High Bridge is a survivor, still towering 123 ft above the Harlem River more than 90 years after some officials first called for it to be torn down. The issue then, at the dawn of the 1920s, was how best to accommodate the larger ships navigating the river that helped to sustain the economy of the rapidly growing city. But to tear down the bridge then would have solved one problem and created another.
At that time the High Bridge still functioned as an aqueduct, bringing water to the city—first via two 36-in. diameter pipes and later through a roughly 90-in. pipe. In the late 1920s engineers reached a compromise and modified the bridge to its unique, Janus-like profile—part Romanesque aqueduct, part elegant steel arch bridge-and thus kept ships moving and the water flowing until 1958. The last of the water pipes to remain in service were left in place as historical relics.
"There was a lot of corrosion in the pipes. Because [they are] historic, we didn't want to damage them further," says Ali Mallick, P.E., the deputy assistant commissioner of the city's Department of Design and Construction (DDC). "What we did was wire-brushed them—very, very lightly. And then we put a coat of paint on."
The historic bridge once again provides a convenient connection between the Bronx and Manhattan. Courtesy of StreetFilms.org
The reopening follows years of inspections, planning, and rehabilitation. Those efforts were spurred by an attempt to reopen the span in time for the 1998 sesquicentennial. But an in-depth inspection commissioned by NYC Parks revealed too much deterioration to put the bridge into service in time for that milestone. "[That] was enough to galvanize us into doing something about it," Macnow says. "We had the idea that it was really time to reopen it. There was really no reason to keep it closed. Nobody can even remember why it had been closed permanently in the first place."
Design work began in 2010 and construction started in 2012. Engineering for the rehabilitation project was provided by the New Jersey office of TranSystems, headquartered in Kansas City. It says something about the remarkably robust nature of the High Bridge that obtaining access for the work was the greatest engineering challenge of preserving the 167-year old span. The bridge, which is 1,450 ft long, now crosses not only the river, but also Interstate 87, a local highway, a local road with sidewalks, and a commuter rail line serving the massive city that grew up beneath it.
"Access was one of our biggest challenges out there," Mallick says. "The access is extremely difficult." The team used plazas on either side of the bridge for staging and moved equipment over park paths. Because portions of the old aqueduct lie beneath that path, the team conducted careful calculations of the weight-bearing capacity and chose equipment that was small enough not to exceed that capacity.
Difficult, rocky terrain presented an additional challenge as the team designed and built the new ramps to make the bridge compliant with the Americans with Disabilities Act. Concrete for the ramp foundations was pumped from the plazas more than 100 ft away. Nightly lane closures were required to site the cranes that placed the approximately 50 ft tall, slender columns that support the steel ramp structure.
The project included extensive repointing of the mortar in the stone arch portion of the bridge, which predates the Civil War. © City of New York
Although the bridge is robust, the years had taken a toll on both the newer steel section and the older stone arches. Extensive shielding and containment were required for the replacement of steel elements and the renovation of the masonry.
"We didn't replace a lot of stones, but we had to do a lot of stone repair," Mallick says. "The historic, deteriorated stone masonry was repaired with 200 square feet of Dutchman and 350 linear feet of crack repair work. The entire surface of the stone masonry was cleaned with a microabrasive process and all of the mortar joints were repointed with natural cement mortar.
"One of the tasks was to clean the masonry span," he adds. "As we cleaned it out, we found more areas where the mortar had come out," crumbling from water pressure. By the time the process was complete, most of the mortar on the bridge had been repointed.
As the rehabilitation began, the team estimated that about 10 percent of the steel would require replacement. After the team completed lead paint abatement on the steel structure, the corrosion was found to be more extensive than originally anticipated; roughly 15 percent of the steel was replaced.
"We had to remove a lot of deteriorated steel members and gusset plates, and all the rivets were replaced with high-strength bolts. And then we had to jack the bridge to replace the bearings," Mallick says. Steel-roller expansion bearings were replaced with new elastomeric bearings; the original granite pedestals were retained.
The High Bridge is listed in the National Register of Historic Places and is also a New York City Landmark. Renovation of such high-profile elements as lighting, brick pavers, and handrails was conducted in a manner "sympathetic to the historic materials," Macnow says.
"Where possible, we restored the original materials. When that wasn't feasible, we matched them," Macnow says. "The bridge is so beautifully designed; both the original, historic section and the 1920s modern section were both really elegantly done and beautifully built. We made an effort to respect that."
The historic handrail was preserved, straightened, and raised two inches to meet current codes. An 8 ft tall safety fence was installed outboard of that. The fence is fashioned from cable mesh to minimize visual obstructions. Custom-made bricks were used to replace damaged units on the walkway.
The rehabilitated bridge features new lighting on the walkway and decorative architectural lighting to highlight the span at night. A series of button lights follow the major elements of the steel span, while flood lights wash the curves of the stone section.
"After years of dedicated effort, the High Bridge now offers a very real connection between neighbors, boroughs, and crucial resources," said NYC Parks commissioner Mitchell J. Silver, F.AICP, at the ribbon cutting ceremony, according to a NYC Parks press release. "Starting today, the people of the Bronx and Manhattan—and indeed all New Yorkers—will once again be able to walk, bike, or simply sit and enjoy this beautiful bridge."