Millennium Tower in San Francisco—the tallest reinforced concrete structure in California—was topped off earlier this year. This 58-story residential tower reflects the many aspects of the changing world of design and construction of tall concrete structures in regions of high seismicity.

The Millennium Tower rises 654 feet into San Francisco’s skyline, and is the city’s fourth tallest building. Designed as a dual lateral resisting system, the structure combines a 36-inch-thick concrete shear wall core with partial perimeter concrete special moment resisting frames (SMRF).

In the world’s regions of highest seismicity, which San Francisco is one, this new era of taller buildings brings new design and construction challenges as well as new solutions. For example, closely spaced conventional ties and hoops in columns and walls create a challenge to the placement of the high-strength, 10-kips-per-square-inch (ksi) concrete. The solution in the case of Millennium Towers was the proven BauGrid Confinement Reinforcement System, similarly used on several 40-story structures in San Francisco.

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