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Tensioning Eases Stress on a 13-Story Sustainability Showcase

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Photo by Michael O'Callahan
Glass-clad 13-story SFPUC building (center) is more costly than a conventional building but is packed with features intended as a model for sustainable design.
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Structural engineer Steven Tipping doesn't often attend industry events, let alone introduce himself to keynote speakers. But he is glad he did just that on Dec. 5, 2007. So is the team for the $145.5-million San Francisco Public Utilities Commission Headquarters, a nearly finished job with a difficult past.

Tipping's actions at the Dec. 5 breakfast—at which a project of his was recognized and he heard Webcor Builders' Phillip Williams speak—inadvertently helped recenter the ailing job. The 13-story showcase for sustainable design and construction owes its existence, in part, to serendipity.

At the breakfast, hosted by McGraw-Hill Construction (ENR's parent) to honor California's "Best of 2007" projects, Tipping was so impressed with Williams' ideas and philosophy that he invited him to come to Tipping Mar's office in Berkeley, Calif.

"I think we are kindred spirits. I'd be tickled to death if we could get together and show you our stuff," the Tipping Mar (TM) president recalls saying to Williams, also a structural engineer.

A month later, Tipping and his partner, David Mar, briefed Williams on TM's performance-based seismic design scheme, adapted from bridge engineering. The concrete shear-wall core system relies on unbonded vertical post-tensioning (PT) in core walls to resist lateral loads and recenter, or re-plumb, the structure after a major earthquake.

TM's scheme is expected to preserve a building, allowing for its immediate reoccupancy. Williams was impressed. "I catalogued it in my brain," he says.

Currently, after weathering three hiatuses, changes in the project team and a cost-cutting design switch from a resilient steel to a resilient PT concrete structure designed by TM, the 277,500-sq-ft building is on course to open at least two months before its late August substantial-completion date.

The decision of the San Francisco Public Utilities Commission to go back to the drawing board midway during construction documents saved $5 million on structural costs alone. And the switch to concrete improved the building, agrees the SFPUC, the architect and Webcor, the job's construction manager-general contractor. "This was that elegant solution," says Williams, vice president of technical systems for the San Francisco-based builder. "One good solution kept on bringing other positive results."

Shaky Start

In 1989, the Loma Prieta quake damaged beyond repair a state building in San Francisco's civic center. In 2000, the city acquired the site for a new administrative building and assembled a design team, led by local architect KMD/Stevens, a joint venture that includes Kaplan McLaughlin Diaz and Stevens and Associates.

The SFPUC put the new building on hold in 2002, following design development, in part because of 2001's dot-com bust, which hit the city's tax revenues particularly hard. Plans had called for a base-isolated building to allow for immediate reoccupancy. The concept engineer was Arup. SOHA Engineers, San Francisco, remains structural engineer of record (EOR).

In June 2006, SFPUC, a city and San Francisco County agency that provides water, wastewater treatment and power, acquired the project. SFPUC's goal was to consolidate 1,000 employees from leased space into a "global model for optimizing energy performance, water conservation and indoor air quality." That meant achieving the top level of the U.S. Green Building Council's Leadership in Energy and Environmental Design rating system: LEED-Platinum.

The SFPUC expects the building, financed by bonds backed by commission assets, to save $3.7 billion in rent over its 100-year life. Besides wastewater treatment and re-use, its green features include power generation via rooftop solar panels and north-facade wind turbines. The facade has daylighting controls, such as fixed sunshades and exterior blinds that move.

In 2006, KMD/Stevens restarted design, with Forell/Elsesser as structural designer for the lateral-load-resisting system. Webcor signed its contract in January 2008, nearly halfway through construction documents. Plans had called for a 12-story building with a steel moment frame with viscous dampers.

Soon, a budget crisis triggered a major value engineering (VE) exercise: Webcor's cost estimate was $62 million over the $133-million "target" budget.

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