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The spur begins at Callowhill Street and turns counterclockwise to cross above 12th and 13th streets on viaducts. The retaining walls between 12th and 13th streets hold enough soil for trees.
"In the case of [this phase] of the rail park, we knew early on that there was no communal green space in the neighborhood," Hanes explained. "What we hadn't really considered, however, was that most people living here are doing so in these really great old factories and warehouses that have been converted to residential uses. They are solid buildings with great, high ceilings and generous windows, but what they don't have is a backyard, a front stoop, a patio, or a garden.
"Not only is there no communal space in the neighborhood, but few residents have access even to private outdoor space," Hanes said. "As they described their wishes, we realized that what they were really describing was an idealized vision of a residential landscape. That became the inspiration for many of the design elements throughout the project."
What Studio Bryan Hanes and Urban Engineers devised is an elevated park that features trees, shrubbery, walkways, wooden steps to serve as seating platforms, and even a set of unusually large swings, all designed with a character in keeping with the city's history. "Most of this is being fabricated from big, chunky pieces of steel and wood timbers to reflect the industrial heritage of the neighborhood," Hanes said.
Urban Engineers had conducted preliminary studies early in the last decade when the city briefly considered demolishing the spur to make way for structures related to a new baseball stadium for the Philadelphia Phillies. The stadium went elsewhere, but when the rail park idea moved forward, Urban was engaged to determine the structural capacity of the infrastructure and to design any necessary repairs or structural additions to accommodate Studio Bryan Hanes's plan. Andrew Van Schooneveld, a bridge engineer with Urban, says the retaining walls and viaducts that supported the rail line are in remarkably good condition for their age. "There are actually different structures that we looked at," he says. "There are two bridges over 13 th Street and 12 th Street, which are through girders with a floor beam trough system, and then there are piers between 12th and Callowhill. There, it's a four-girder system topped with floor beam troughs. It's sort of a typical construction of the old days—built-up plate girders that are riveted together," he says. Between 12 th and 13 th streets, the structure is supported by a pair of retaining walls rising from grade level that contain fill and soil, he explains.
The engineers found that the infrastructure as a whole is quite robust. "It was designed for the old railroad loading, so the main part of the viaduct is well overdesigned for what we're using it for today," Van Schooneveld explains. The floor beams on the bridges did exhibit some rusting and delamination, however. "We're going to cap that whole system," Van Schooneveld says. "We're going to pour a concrete slab over the entire aboveground structure." A waterproofing membrane will be added to prevent any additional damage from moisture.
Ironically, some of the worst damage sustained by the structure is of recent vintage; a truck hit the overpass above Callowhill Street, damaging the exterior girder. That girder will be replaced as part of the project.
Urban will also make additions to the structure between Callowhill and 12 th , where it will add 5 ft cantilevers to accommodate overlook points and plantings, features that Hanes likens to residential window boxes.
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