The company's technology makes it possible to prefabricate thin-shell concrete panels that are only two and a half inches (64 millimeters) thick, supported by light-gauge, cold-formed steel framing. Shear-transfer strips join the concrete and the metal framing to create a panel with composite strength.
Bert England, lead designer for the project and senior vice president of Earl Corporation, explains the panels' construction: The shear-transfer strip, he says, "is fabricated from galvanized steel sheet. The strips are screwed onto studs, and their Y-shaped flanges are embedded into the concrete to produce an economical and reliable composite panel."
Using the thin, lightweight panels, England continues, "enabled us to get the aesthetic and functional benefits of precast concrete without the normal limitations of the material. The panels were engineered to move independently from the structural steel frame, to resist cracking due to building movement, yet provide the long-lasting quality and appeal of concrete."
The panels' weight and strength made it practical to transport and erect panels up to 16 feet tall by 40 feet long (4.8 by 12.2 meters), much larger than most other wall panel systems. "It was very aggressive to make precast panels this large," says Bob Konoske, vice president and general manager of precast subcontractor Coreslab Structures, Inc. He explains that precast panels typically do not exceed 8 by 20 feet (2.4 by 6.1 meters).
"If these panels were a more conventional 4-1/2-inch- (114-millimeter-) thick precast concrete," Konoske says, "they would have been much heavier. Practically, we could not have made conventional panels this big; the panels would have had to be smaller, and more joints would have been exposed."
It is estimated that using the thin-shell composite precast panels reduced the length of joints on the Research Center by about 40 percent. Fewer joints, coupled with closed-cell foam insulation spray-applied to the interior of the panels, helped achieve a moisture barrier and thermal break, minimizing air intrusion and maintaining the required environmental conditions.
The large panels had to be shipped on a slanted easel at a 35-degree angle so they would stay under highway height and width limitations. Initial concerns that such large panels would be fragile were allayed after this test of their durability: surviving the 80-mile (130-kilometer) trip from Coreslab's plant to the project site without a single crack. There was also no cracking during installation, which was accomplished with a mobile crane.