100 College Street Parking Structure
The new total-precast concrete parking structure being built adjacent to a new biomedical building in New Haven, Connecticut, featured unique challenges, due to its siting over a connector road to the highway still used for deliveries to nearby buildings and access ramps to the facilities. Fabricating the precast concrete components off site and using other precast concrete components to span the roadway minimized congestion and is speeding construction.
“This was a challenging project because of the tight site and the roadways that run beneath the building that are still active,” explains Todd McCoy, chief operating officer at engineering consulting firm TRC Worldwide Engineering. The design featured a precast concrete structural system with long spans in the first levels to work around the various ramps and roadway, which had to be closed during the work. On upper levels, the design resembled a more typical parking structure, he notes.
The nine-level, 850-car parking structure is designed for use by tenants in the adjacent biomedical building, which also is being constructed. The $100-million project, which connects the downtown area to the nearby medical district, was made possible in part through a $16-million federal Tiger II grant that allowed the city to fill in parts of the unused roadway beneath the complex.
The lateral-load system used for the approximately 325,000-square-foot structure consists of a heavy moment frame of precast concrete columns and beams in one direction. It was fabricated in pieces and brought to the site, where it was spliced together to create a monolithic structure. “It works almost like a bridge format to span the road,” McCoy says. “We discussed having it built in pieces as the structure was erected, but we decided to build the frame at once to gain the full lateral stability.” Unistress Corp. fabricated the components for the parking structure.
The first level features a “maze” of ramps used by the nearby hospital for deliveries as well as for shuttle buses that drop off visitors. The spans over the roadway were designed to handle heavy loads, with a 5-inch topping slab to ensure tight waterproofing. “The first level is far from typical, but after that, it’s a more typical design that we would design,” he says.
A complicating factor arose when the developer decided to create a green roof filled with plantings after design work had commenced. This required the addition of a precast concrete roof, as the structure was initially designed with an open-air top level of parking. “We had to return to our analyses to recalculate the vertical loads and ensure the framing could support the additional load of the new level and soil,” he says. “We had to be sure we didn’t have to redesign the lateral loading and add precast concrete to the design to support it.” As it turned out, the size of the specified columns was sufficient to handle the new load by using 9,300-psi concrete combined with added rebar.
As it turned out, the size of the specified columns was sufficient to handle the new load with some rebar added to the components.
The precast concrete spandrel panels feature a standard gray exterior finish. One side faces the adjacent office building and is mostly hidden from view. On other sides, spandrels were connected outside of the columns using hidden corbels, which allow them to appear to be floating away from the structure. They create a visually arresting addition to the structure that will help it fit with the high-tech nature its adjacent biomedical building.
The project supports the adjacent biomedical building, for which Alexion Pharmaceuticals is the largest tenant. The two structures are part of a larger program intended to completely fill in the Route 34 Connector to create a new street plan and additional developments. This first phase is planned for completion in 2015, when Alexion will transplant its 350-person workforce to the building.