High Concrete Group LLC has introduced ThinCastTM, the thinnest precast concrete rainscreen panel available on the market. Designed for use in commercial, institutional, retail, and low- to high-rise construction, this innovation provides architects with the natural beauty and character of concrete in lightweight panels that accomplish their rainscreen design goals.
Size: 116,000 sq. ft. (159 curved architectural wall panels, 118 double tees, 15 beams, 47 columns)
Type of Precast: architectural and structural
Innovation in structural and mix design made all-precast construction the ideal choice for the industrial-age look of COSI.
The unique design of the new Center of Science & Industry (COSI) in Columbus, Ohio, required innovative techniques to clad the building with precast concrete wall panels. Located along the Scioto River, the $125-million, 326,000-sq. ft. project integrates the eastern portion of the classic limestone Central High School building with a modern addition featuring an atrium, an IWERKS large format theater, a space theater/planetarium and 116,000 square feet of exhibitions.
Some of the excitement for this project centers on its internationally renowned architectural designer, Pritzker Prize-winner Arata Isozaki & Associates of Tokyo, Japan, along with Moody/Nolan and lead architectural firm NBBJ, both of Columbus. Ruscilli Construction Co. in Columbus served as construction manager on the project, with High Concrete Group’s Springboro, Ohio plant consulting on the design phase and then designing and supplying the precast concrete components.
The shape of the building itself is a mathematics teaching opportunity. The building’s west façade is designed as an elliptical curve, featuring a discontinuous “clothoid” curve from ground to roof. The curve, defined as a segment of a spiral, required precast concrete wall panels essentially in a shape similar to a tangerine’s sections. Each quadrant of precast panels making up the facade was placed along segments of six circular curves to produce the buildings elliptical shape. All this was accomplished without the benefit of 3D modeling tools, which were not available at time the design was completed.
The architectural drawings and concepts were translated into High’s shop drawings and required considerable discussion and tweaking to complete. Throughout the project High worked closely with the design team and many other prime and subcontractors to coordinate the work. According to Dave Campbell, design coordinator for High’s Springboro, Ohio plant, which produced the architectural panels, the paper correspondence in the engineering file alone stood 20 inches thick, while the stack of design calculations for all the precast products, form design, handling devices and shipping rockers was only five inches thick. There were over 900 requests for information and 150 changes during the project, about six percent involved precast. “At times the phone calls and meetings seemed endless, but everything had to work properly to be a success,” says Campbell.
The back sides of the precast panels consisted of two vertical stems and three or four cross-ribs, with massive steel assemblies and post-tensioning embedded in the concrete for erecting and aligning the panels at the site. The post-tensioning had to be carefully positioned to avoid changing the shape of the panel, Campbell notes. Panels were cast on a one-day cycle of about 11 hours start to finish, requiring significant post-tensioning design to accommodate the handling and erection loads.
With these additional lift points, the erection sequence involved two stages. First, the panel was tilted up in the typical manner, allowing it to hang in the air with the bottom tucked under the top somewhat. “At this point in the erection, as the panel hung in the air, its shape and weight tried to straighten and stretch it under its own weight,” Campbell explains. “We had to add up to 9 post-tensioning tendons to prevent cracking the panel at this stage.”
Because of their 25-foot height, the round precast supporting columns were cast horizontally in two stages. The first half-circle half was cast, then turned over and embedded in the fresh concrete of the second half.
One of the beams measures 52 inches wide, 30 inches deep and has an 11 foot cantilever which required a prestressing force of 1.33 million pounds (at the top), the highest prestressing force High’s Springboro plant had cast to that point in time.