Base isolation technology makes city hall quake-ready
The 1989 Loma Prieta earthquake cost Hayward, Calif., its city hall. After the quake, the old building was abandoned as unsafe. Consequently, when Hayward, Calif., residents and local officials decided that a new city hall would be a good way to jump-start downtown revitalization, they knew they would have to make it earthquake-proof. (The site selected for the new city hall was just 700 feet from the Hayward Fault, an offshoot of the San Andreas Fault.)
They are pretty sure they got it right this time. Hayward’s new $29 million city hall is constructed on an elaborate three-part base isolation system that will allow it to survive a 7.5 magnitude quake. Buildings atop base isolation systems move with the earth during a quake, while buildings on conventional foundations remain static.
The columns for Hayward’s city hall were placed atop 53 friction pendulum base isolators that are designed to allow the building to move up to 22 inches in any horizontal direction. Fifteen viscose dampers act as shock absorbers, and a 2-foot moat encircles the four-story, 100,000-square-foot building, allowing it to “float” with its structure intact. The concrete, below-grade parking facility is heavily reinforced.
The building’s design required that all mechanical, fire protection, plumbing and electrical systems be flexibly attached to the basement. Furthermore, the elevator and stairs into the parking garage had to be attached to the building above so they could move with the structure during a quake.
Fifty-three 6-foot-square, reinforced concrete columns – each capped with a concave stainless steel plate – rise from the garage slab to the ground level. The building itself sits on top of a separate concrete slab fitted underneath with 53 semicircular, stainless steel friction bearings that fit into the steel plates.
More than $1.2 million worth of recycled materials were used in the construction of the building. Sixty percent of its roof consists of recycled scrap copper; the ceiling’s acoustical panels are composed of recycled paper; and recycled steel was used for the acoustical tile lay-in tracks. Recycled paper drywall was used throughout, and ceramic tiles containing recycled glass were used in the building’s restrooms. All building materials are American-made – most visibly, the Minnesota limestone exterior and the South Dakota granite interior.
The city hall includes a two-story galleria dedicated to the display of community art. The city council chambers, which feature high-tech audio/visual equipment, double as public meeting space, and an outdoor terraced amphitheater provides space for community events and performances.
Heller*Manus Architects, San Francisco, designed the building, which won an engineering award in 1998 from the Golden Gate Branch of the American Society of Civil Engineers, San Francisco. The base isolation system was designed by KPFF Consulting Engineers, San Francisco. The city hall was built by DPR, Redwood City, Calif.