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'Body Brace' on Stilts Keeps Old Building Safe

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Keeping an Art Deco printing plant administration building out of harm's way while a $100-million museum is built under, in and around it requires some fancy falsework and delicate footwork. In October, crews at the University of California, Berkeley site finished installing a "body brace" on stilts to both protect the three-story shoe-box-like structure, which anchors one corner of the museum development, and to make room for new foundations and a new basement gallery space.

Photo by Scott Blair
Crews dug a new basement level underneath the shored-up Admin Building at the site of Berkeley's new art museum.
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"The admin building is retained as a found object that is absorbed by the new construction and repurposed," says Ben Gilmartin, principal with Diller Scofidio + Renfo, New York City, design architect for the Berkeley Art Museum and Pacific Film Archive (BAM/PFA) project.

The repurposing is forcing some careful maneuvers on the part of the building team, led by San Francisco-based Plant Construction Co. For starters, the 125-ft x 37-ft admin building could not move during construction, so it needed propping in place. Complicating matters further, the old building shares a new mat foundation with the rest of the project. "Whatever temporary structure we put in place to hold the building [will] remain out of the way of the new foundations," says Dylan Berry, Plant's senior project manager.

Conventional internal shoring would have impeded construction of the 33,000-sq-ft mat, which is now complete. But the demand for zero movement and the unconventional shoring system prompted bidders to add a "fear factor" to their prices.

"There weren't a lot of bids on it because it's a scary piece of work, and frankly, not too many contractors could pull it off well," says Berry. "When bids came in for the shoring, they were—surprise—over budget."

As it turned out, Condon Johnson Associates in Oakland—the successful bidder—not only took on the challenge, it saved $250,000 by reusing steel from earlier jobs. The reuse of the steel helped bring the project back on budget.

Condon Johnson "provided measurements of all the material in the yard and said 'Make this work,'" says Andrew Scott, principal in charge for structural consultant Degenkolb Engineers, which engineered Plant's shoring scheme.

The falsework is a three-dimensional gridlike system of 3-ft-deep girders and columns that form a partial jungle gym-like frame through and around parts of the old building. The girder system, which props some areas and suspends others, bears on 70-ft-deep perimeter soldier piles. The horizontal components penetrate the building, spanning as much as 60 ft through opposite window openings. Workers installed most of the girders through the openings to avoid disturbing the architecture.

Since the needle girders were expected to deflect by 2 in. to 4 in. under load, Degenkolb had to find a way to keep the building from sagging with them. "We created an interesting sequence to jack [the girders] into place," Scott says. "We did it in a sequence to basically force that deflected shape into the girders but left the building as it was prior."

Jagged Top

Plans initially called for an adjacent former printing press building, with a sawtooth roof profile, to remain intact during construction of the new basement underneath it and the admin building. The team ultimately rejected that strategy, mostly because the site is about one mile from the Hayward fault.


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