Rehab Praised For Seismic Ingenuity
Rehab Praised For Seismic Ingenuity
Bronstein, College of Engineering
"An outstanding renovation," is how California Construction Link, a McGraw-Hill Companies magazine for contractors, described the $67.6 million Hearst Memorial Mining Building renovation in its December 1999 issue. Calling the project "an award-winning combination of base-isolated seismic strengthening, critical program improvement, and interior remodeling," the publication chose Hearst for their "Best of 1999" award, praising the project as "taking great care in preserving the building and implementing the kinds of structural strategies to ensure the building will be there for a long time."
The structural strategy designed to protect the campus's most prized historic building is a base isolation system pioneered at Berkeley more than 20 years ago. When completed, 134 base isolators will be installed under the building -- technology to help the building ride out violent quakes with its beauty and structure intact.
Located just 800 feet west of the active Hayward Fault, this 1907 Beaux-Arts masterpiece was likely to be damaged beyond repair from even minor temblors. "The seismic retrofit should reduce the impact of a large quake on the building from almost certain destruction to repairable damage," says Rob Gayle, project manager of the building renovation.
A walk along the building's northwest perimeter reveals a forest of steel piers beyond the mounds of excavated mud. As of last month, 500 piers had been drilled down 30 to 45 feet into the earth. The piers (there will be 600 total) provide a temporary shoring system as the building's load is transferred to the base isolator system. By last month, 11 base isolators were in place in the northwest quadrant of the building (visible from Bechtel), each surrounded by a quartet of cut-to-size piers that form the base isolator foundation. It will take about a year to install the remaining isolators and piers, then transfer the building onto its new foundation.
"We're disconnecting the old rigid connections to the earth," says Jake Skaer, on-site project coordinator. While the base isolator's top and bottom steel plates are fixed, providing a rigid connection to the building and the earth, the central rubber/steel bearing is flexible. A three-foot wide dry moat rings the building, providing a wide berth within which the isolators can move up to 28 inches in any horizontal direction. With this elastic foundation, builders can save the seismically vulnerable brick masonry walls instead of replacing them with shear wall. "This," says Skaer, "allows us to maintain the building's architectural integrity."
While isolators are installed under the building, workers inside are busy on every floor of this four-story gem of a building. On the northwest side of the first floor, workers are refashioning an old ramp into a handicap entrance. On the second floor in the elegant Memorial gallery, the original Douglas fir window frames and doors are being removed for restoration. Each pane of glass in the enormous skylight above has been inventoried, evaluated, then removed for repair.
On the third floor, workers are demolishing an old stairway, torching off re-bar as they tear down some walls and strengthen others -- part of an extensive 1948 renovation. This demolition will restore the building's original light courts, exposing interior walls to natural light for the first time in 50 years. Later this space will be designed as graduate work stations -- 70 of them -- open to the skylight above.
And on the fourth floor, new trusses are being installed, fabricated to match the building's 1907 originals, and the damaged central skylight is being repaired.
Finally, it is hard not to notice the scaffolding erected to reinforce the roofline's chimney system. Workers there are drilling cores through the 20 chimneys, then dropping in high-tension steel strands from the chimney caps to attach to anchor plates at the bottom.
The project is scheduled for completion by fall 2001. For information, send e-mail to email@example.com.