Structural Engineering Award of Excellence: Wilshire Grand Center, Los Angeles

Paul Fu
Senior Principal
Thornton Tomasetti, New York City

Performance-Based Seismic Design Drives an Elegant Form

The Wilshire Grand Center employs a number of structural innovations simultaneously, to achieve a narrow-footprint, mixed-use tower that would meet the stringent seismic requirements of Southern California. Key to all of the elements was a performance-based seismic design (PBSD) approach. In addition to validating the tower’s seismic performance, it eliminated the need for prescriptive perimeter moment frames, which in turn allowed floor-to-ceiling glass for great views and natural light. A mixed structural system minimized weight and construction time. Steel floor beams span from an internal concrete core to the perimeter concrete-filled steel box columns, which, between pairs of hotel rooms, carry the concrete-filled metal deck slabs. The core, a nearly rectangular four-cell cast-in-place reinforced-concrete shear wall tube, provides lateral load resistance. The middle outriggers, consisting of “braced Vierendeel” trusses six stories tall, used extensive modeling to determine peak connection forces and special detailing to accommodate large deformations. The middle outriggers are designed to be “invisible” by fitting within hotel room walls, while avoiding guest-room floor corridors.

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