A Fix for Memorial Stadium
If the Hayward Fault ruptures during a Cal home game, Memorial Stadium fans would be in for a wild ride. But they should be safe—even if they’re seated in the most vulnerable end-zone sections.
That’s the outcome that David Friedman (B.S.’75 CE) envisions for the massive retrofit of UC Berkeley’s landmark but seismically poor football venue. Friedman, senior principal at San Francisco–based Forell/Elsesser Engineers, is the lead engineer for the stadium’s renovation. Built in 1923, Memorial Stadium straddles the Hayward Fault and is in need of seismic upgrades.
Charged with bracing the structure for a massive quake that could trigger a six-foot rip in the earth’s surface, Friedman and his team have taken what they consider a unique—and effective—approach.
They want to carve the two end-zone sections sitting directly over the fault into wedges, each separated from the rest of the stadium bowl by a five-foot gap. Specially built to be sturdy and self-contained, these “fault rupture blocks” are meant to ride out a major quake without collapsing. “It’s going to be a stiff structure, like a bunker,” Friedman says. During a major temblor and possible fault rupture and displacement, “these blocks would do nothing more than rotate and tilt but be life-safe.” The five-foot gaps between the stadium and the fault rupture blocks would be covered by sliding and articulating plates.
Built at ground level, each fortified block would rest on plastic sheets covered by a 30-inch-thick concrete mat. This would allow the structures to be independent of the potentially rupturing fault and move freely from any tearing motion of the ground.
The Hayward Fault stretches for more than 40 miles through the densely populated East Bay. Scientists from the U.S. Geological Survey have described it as a “tectonic time bomb” that is due any time now for a 6.8- to 7.0- magnitude earthquake.
Cracks in the stadium walls have long pointed to the fault’s location, now meticulously mapped by geologists. “The stadium is trying to tell us something about where the fault is,” Friedman says. Bisecting the length of the playing field, the fault runs under Sections AA to WW at the stadium’s north end and Sections K to LL at the south.
Friedman’s firm, which engineered rehabilitations of Berkeley Civic Center, San Francisco City Hall and San Francisco’s Asian Art Museum, began working on seismic corrections to the stadium in 1999. The firm oversaw the removal and temporary replacement of the stadium’s press box in 2002. Just west of the stadium, Forell/Elsesser is also engineering the new Student-Athlete High Performance Center. Following litigation and a 21-month tree-sitting protest, that project is now under way.
Later this spring, Friedman expects to complete schematic designs for the stadium component of the project. The stadium’s west side, which sits off the fault, will undergo a more conventional retrofit to withstand strong ground movements. While the historic outer wall will remain, the structure behind it will get a new foundation, shear walls, press box and stadium bowl. The east side of the stadium is carved into the hillside and doesn’t require retrofitting.
The campus’s Seismic Review Committee (SRC), which includes preeminent earthquake and geotechnical experts from Berkeley Engineering, has endorsed Friedman’s and Forell/Elsesser’s engineering concept.
“They are using good engineering principles to ensure good performance,” says Professor Jonathan Bray, a leading authority in fault rupture mechanics and an SRC member. Bray has studied how bunker-like structures can actually deflect the path of a rupturing fault. “Because they’re strong and the ground around them is weak, the ground fractures go around them,” he says.
Craig Comartin, the campus’s structural and seismic consultant and another SRC member, calls the design approach “very simple and very effective.”
The campus hopes to present the Memorial Stadium plan to UC Regents for approval within the next six months, says Vice Chancellor Edward Denton, who oversees capital projects for the campus. Financing will come from private sources. Denton says the campus would like to start construction in 2011–12.
Although Friedman describes Memorial Stadium as an “engineering challenge,” he has confidence in his response. “After the retrofit is complete,” he says, “if there’s an earthquake on a game day afternoon, I’ll be happy to be in that stadium.” A Bay Area native and holder of Cal football season tickets, Friedman also serves on the Department of Civil and Environmental Engineering’s Advisory Council and the UC Berkeley Foundation.
For a detailed description of the engineering behind the planned retrofit, see Jack Moehle’s 2008 Homecoming talk, The Science Behind the Stadium. Moehle is professor of civil and environmental engineering at UC Berkeley and former director of the Pacific Earthquake Engineering Research Center.