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Golden Nuggets: Memorial Stadium Upgrades Limit Potential Impacts from the Hayward Fault

How do you create a safe, reliable structure that sits directly on top of a fault line?  Thanks to the expertise at the Berkeley Seismological Lab, the architects helping to renovate Memorial Stadium have an answer: create four separate, movable sections that will isolate the impact of seismic activity to prevent total structural damage.

Part of the historic nuance of the stadium is the fact that it was created in one continuous bowl all the way around, a style that is not seismically viable. In the renovated stadium, the bowl will be split into four separate parts.

The East Rim, which includes the student section, will remain the same. But the West Rim is taking on a whole new structure. The designers have reclaimed the space that used to be the hill of dirt under the western rim and, in doing so, have been able to provide a much more flexible base of a complex weave of concrete and rebar.

In between the two sections will be two wedges, with a foot of space separating the wedges from the rim sections. These two wedges, built like bunkers, are positioned right on the fault, so if there is a seismic event, only the wedges will move. Each wedge is constructed with a thick slab foundation and built over layers of sand and High Density Polyethylene plastic sheeting to allow it to move freely in response to the up to six feet of lateral movement occurring below it.

"You don't want to anchor a structure on both sides of a fault. You want to ride above the fault," said Vignos. "But if you make a very stiff, strong structure, almost like a bunker, and the ground breaks underneath it, it will just move. It might tilt, it might rotate, it might shift, but it won't have problems internally. It'll just be out of place when the shaking is over."
The new press box will also be seismically sound. The steel structure, which takes much of its inspiration from the design of bridges, will be placed atop four massive cores that are anchored to the foundation with high strength cables and are only connected to the bowl sections below by large shock absorbers. In the case of an earthquake, these shock absorbers would absorb much of the shock, transferring it to the seating bowl below and allowing the press box to sway back and forth without breaking apart. 

Go here to see a gallery with illustrations of the locations of the stadium's four sections as well as a cross-section of the press box's support columns.

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