The first major federal courthouse built since the 1995 blast in Oklahoma City, the Lloyd D. George United States Courthouse contains features intended to prevent a catastrophic collapse in the event of a terrorist attack.Key components in this defense mechanism are 420 precast panels manufactured by Clark Pacific, a West Sacramento, Calif., producer of architectural and structural precast panels for design/builder JA Jones Construction Co. of Charlotte, N.C. Clark Pacific, owned by James Clark, Don Clark, P.E., and Robert E. Clark, P.E., helped engineer the panels as well as the connection system that ties them to the underlying steel frame.
"What the design team was searching for was a system in which the precast panels could absorb as much of the bomb blast as possible without just destroying the connections that tie them to the structure," says Eve Hinman, P.E., president of Hinman Consulting Engineers.
The panels for the new Las Vegas courthouse were designed to be more ductile than conventional panels so that they would absorb the loads generated by a blast. "The stiffer the panel, the more it transfers load to the connections holding it to the steel structure underneath," explains Kim R. Hammon, P.E., chief engineer for Clark Pacific. "Our task was to design panels that would take the blast without transferring all of that energy to the connections. Thus, the panels would fail individually, but the type of progressive collapse that doomed the Oklahoma City building would be avoided."
Working together, Clark Pacific and Hinman designed the precast panels as well as the connector system that fastens them to the steel frame underneath. The panels feature either of two architectural finishes: limestone cladding or a sandblasted exposed-aggregate finish. The 110,000 square feet of precast panels include 96,000 square feet of exposed-aggregate panels and an additional 14,000 square feet of panels faced with factory-installed limestone cladding.
The huge precast panels feature an integral vertical ribbing system. These ribs, monolithically cast into the panels at the Clark Pacific plant, are spaced about 6 feet apart.