When designers began planning the new six-story U.S. courthouse in Greenville, South Carolina, they wanted a design that would convey the dignified presence of a federal building and deliver enhanced security, durability, and energy efficiency. They initially considered limestone and brick masonry with cast stone accent components, but they recognized that precast concrete was a better option because it offered a feasible means to provide texture and articulation on the significant solid wall areas, while staying within budget requirements and schedule demands.
“The move from traditional masonry to precast concrete aided in streamlining the components that made up the exterior envelope and thus produced cost savings in terms of labor and materials,” says Neil Sondgeroth, architect and senior associate for HBRA Architects.
The final design features a limestone architectural precast concrete facade fabricated to represent Indiana limestone with an ashlar pattern, and traditional stone detailing, with layers of texture, and across large-scale precast concrete panels.
“The historical profiles that we used are often seen carved into materials rather than cast,” Sondgeroth says. “One of the challenges was to fine-tune the pieces and profiles to create elegantly shaped forms that were also technically feasible.”
Filtered light streams in
Throughout the main building, contrasting bands of formed finish and other finishes create a layered composition that, along with the ashlar pattern and profiles, helps balance the scale of the large structure. Formed dentils and reeded profiles accentuate and separate the facade’s high floor-to-floor levels.
The use of high vertical windows for day lighting flanked by articulated precast concrete panels creates a vertical expression for the building’s elevations. This is further emphasized on the north facade with the expression of the central conference room wing, which terminates at the sky with a precast concrete tower element that conceals mechanical rooms and equipment. Deep precast concrete panels with recesses on the sides of the tower create monumental columns that filter daylight indirectly into borrowed light corridors and courtrooms.
To ensure quality and consistency, the precaster modeled and reviewed every precast concrete piece with the architect before finalizing and producing the panel. In production, the precaster used multiple form setups within the precasting facility to stay on schedule and to maintain control and consistency of the finishes and aesthetic features on the project. The use of large panels with minimal and repetitive connections allowed the precast erector to install the panels efficiently.
Once produced, the facade panels had to be secured to the structure’s cast-in-place (CIP) columns, beams, and continuous CIP shear wall without marring the aesthetic. Through close coordination with the contractor, the precaster placed small holes through the shear walls by using pockets at the bottoms of panels that could combine bearing and lateral connections, whereas the top connections face the shear wall. The bearing connections in the pockets feature knife plates to minimize the profile, with a PSA strap for lateral connection. This arrangement helped minimize the required blockout size on most of the structure. In longer spans, intermediate connections were used to resist typical wind loads.
“From the beginning of the shop drawing process, HBRA Architects worked closely with Gate and the construction manager to advance the architectural details in our design drawings in a way that would work successfully in precast concrete,” Sondgeroth says. “The result was an envelope that was both physically durable and architecturally robust.”