Stacked Up: 185 Berry Street at China Basin
May 1, 2008
Building Design and Construction
Since the first application of base isolators some 23 years ago on a legal
services center in Rancho Cucamonga, Calif., the technology has become a
popular seismic design approach throughout the West Coast. The technique
is fairly simple: construct the building atop a series of elastomeric bearings
or sliding friction plates, thereby separating the structure from its base and
the unstable ground.
Until recently, base isolation applications have largely been limited to
separating structures from the ground. All that changed four years ago when
San Francisco-based real estate company McCarthy Cook commissioned a
Building Team to design and construct a two-story addition atop its three-
story office building at 185 Berry Street in the city's China Basin district.
Construction could not disrupt the activities in the nearly fully leased building
below, where tenants included several University of California, San Francisco,
bioscience laboratories. That caveat all but eliminated the possibility of
applying conventional seismic construction methods, says John Sumnicht,
SE, principal with engineer Simpson Gumpertz & Heger, which teamed with
the local offices of architect HOK and contractor Hathaway Dinwiddie
Construction on the 150,000-sf addition.
“Conventional upgrade approaches would have involved the addition of new
reinforced concrete shear walls throughout the structure,” says Sumnicht.
“That would have been highly disruptive to the bioscience laboratories
operated by UCSF.”
To minimize disruption, the project team devised a solution that involved
constructing the two-story, steel-frame addition on seismic isolation bearings
over the roof of the existing concrete-frame structure. Instead of having the
existing building and the addition work as a single monolithic reinforced
structure, this approach separated the two, with the new structure acting as
a giant mass damper.
“During strong earthquake sh