Seismic framing technology and smart siting aid a California community college
By Deborah Snoonian, P.E.

	Click images to see larger view
	Lighting animates the health sciences building and emphasizes its angles.
	The triangular roof form of the life sciences building shelters an informal gathering space. Photography: © Milroy & Mcaleer

Several years ago, during a seismic study of the San Bernardino Valley College (SBVC) in California, engineers discovered that a portion of the San Jacinto fault, a branch of the San Andreas fault system, lay right underneath the school’s campus—endangering the integrity of nearby buildings and threatening the safety of students and faculty. With the help of design architect Steven Ehrlich Associates, along with engineers at Arup and associate architect Thomas Blurock Architects, SBVC recently opened three new buildings that employ unbonded brace frames, or buckling-resistant frames, as they’ve come to be known, a Japanese technology that’s been making inroads in U.S. seismic design for the past five to six years. The new buildings are part of a larger master plan and rebuilding effort that reflects and even celebrates the existence of the fault under SBVC’s 60-acre campus.

More strength, less material

The three new structures—a health and life sciences center, a library and learning center, and an administrative and student services building—opened earlier this year. (An arts center and campus center, also designed by Ehrlich and his collaborators, are slated for completion in 2006.) They share a common material language of structural steel, glass and metal panels, and stucco cladding; their angular, dynamic volumes, folded roof plates, and triangular forms are meant to suggest the plate tectonics of the shifting ground planes they sit on. “This was a unique opportunity for the architects and the college to change an entire campus with a consistent voice,” Ehrlich says. He and his collaborators worked closely with the SBVC community to solicit input on what the new structures should look like.

All the buildings are framed in structural steel, made in the U.S., and augmented with the buckling-resistant braces, which were made in Japan. Unlike typical structural steel braces, buckling-resistant braces perform as well in compression as they do in tension. The brace consists of a steel core, typically in a cruciform shape, slipped inside a steel sleeve or tube filled with lightweight mortar. A special coating is applied to the core steel so that it doesn’t adhere to the mortar, meaning the core can slide back and forth, much like a piston, inside the tube. When tension forces are applied, the brace can elongate like a traditional brace as the core slides within the tube. When hit with compression forces, the combination of the mortar and steel core provides enough stiffness and strength to prevent the brace from buckling, which can reduce the stiffness and strength of the entire building, leading to catastrophic collapses.

The buckling-resistant braces have other advantages, as well. They allow the structural frame to be built using less steel overall, but more important, their increased compressive strength simplifies the design of member connections and lowers the foundation’s strength requirements, says Atila Zekioglu, a principal at Arup’s Los Angeles office and the structural engineer on the SBVC project. Although the design team also considered using concrete shear walls for lateral stability, the weight and thickness necessitated by the fault’s location made them infeasible both aesthetically and technically.

The buildings are strong enough to withstand earthquake forces twice the force of gravity in the lateral direction. To put that in perspective, the buildings would be structurally sound if they were turned on their sides and acted structurally as cantilevers, Zekioglu says.

Planning for future growth

Arup’s Los Angeles office has been consulting with SBVC on seismic and geotechnical issues for more than 10 years, and the architects tapped the firm’s expertise not only for engineering the new buildings, but also for finessing tricky siting and planning issues.

As per state code, SBVC had to establish a no-build zone within 50 feet of the fault trace on each side; as a result, seven existing structures were razed. At a design charrette early in the project, Zekioglu explained to the design team that the strongest forces during an earthquake run either parallel or perpendicular to the San Jacinto fault line. He recommended that the master plan require new buildings to be aligned in these directions (rather than the existing campus grid) to reduce torsional forces on the buildings in the event of an earthquake. This decision also uses open land efficiently around the swath of the no-build zone, which is at least 150 feet wide in some areas of campus.

A changing field

The rebuilding effort at SBVC may serve as a template for the design of future buildings in seismically vulnerable regions. The three new structures are the first approved by California’s Division of the State Architect (DSA) that use buckling-resistant braces, and perhaps more critically, the first to employ performance-based seismic design rather than relying on prescriptive building codes. The codes can be troublesome because they don’t always accurately reflect what’s going on at a particular site. “At SBVC’s campus, the general seismic hazard code underestimates the severity of possible seismic activity at the campus by 100 percent,” Zekioglu says. Arup’s design experience with the new braces, which began several years ago when they used them in projects at U.C. Davis and U.C. Berkeley [record, October 2002, page 185], helped convince state officials that they’re a proven method. “Advocating any unique system requires intense investigation and collaboration,” he says, “but DSA is breaking new ground here. We’d be happy to see other projects follow suit.”

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