Seismic engineers apparently have solved one of the world's great retrofit puzzles: how to keep the University of California at Berkeley's Memorial Stadium from crumbling into a pile of concrete rubble during a major earthquake.
BERKELEY, Calif. — Seismic engineers apparently have solved one of the world’s great retrofit puzzles: how to keep the University of California at Berkeley’s Memorial Stadium from crumbling into a pile of concrete rubble during a major earthquake.
It took decades of research, experimentation and head-scratching, but a team of San Francisco engineers says it has found a way to save the beloved landmark in Strawberry Canyon, which straddles the state’s most dangerous earthquake fault.
“I’ll sleep well at night, even if I have season tickets in Section KK,” said David Friedman, leading engineer on the long-awaited Memorial Stadium retrofit project. “We’ve come up with a unique solution to a very unique problem.”
The plan, which is expected to get under way in the next year or two, calls for portions of the stadium to be sliced into blocks that will rest on plastic sheets. When the earth ruptures, the soil will move under the sheets but, engineers hope, will leave the blocks intact. The price tag for the retrofit is estimated at between $150 million and $175 million.
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“If there’s a quake during a football game, people sitting on those blocks might be seated a little differently after the quake, but they’ll be safe,” Friedman said. “We can’t prevent the building from moving or cracking, but we can save lives.”
Memorial Stadium was built in 1923 atop the Hayward Fault, which the U.S. Geologic Survey said has a 70 percent chance of hatching a 6.7-magnitude or greater quake by 2030. The earth could move up to 6 feet horizontally and 2 feet vertically, presenting a challenge to engineers charged with saving the stadium and the football fans inside.
While plenty of buildings around the world sit atop earthquake faults, Memorial Stadium is unique because of the sheer quantity of people it holds: 75,662. It’s also unique because seismologists know exactly where the fault lies — under Section LL, through both end zones and out Section XX.
Adding to the challenge is the stadium’s architectural and historic merit, which prevent engineers from ordering major overhauls of the building’s exterior. Designed by John Galen Howard, the bowl is on the National Register of Historic Places and is widely considered the most beautiful college football venue in the country.
But it’s also the most perilous. The eastern half is built into the hillside and does not need a retrofit, but the western half, with its Beaux Arts flourishes and spectacular views of the hills and bay, rests precariously on landfill over a creekbed. Its concrete walls are cracked and strained, as the Pacific Plate, which is under Sections M through XX, inches south and the North American Plate, under Sections MM through X, creeps north.
The problem has vexed engineers for decades. At various times, the campus has considered building a giant steel net under the stadium or filling the stands with sand.
But the model the university finally chose is notable for its simplicity, said independent structural engineer Craig Comartin.
“It’s a complex problem but it’s a simple and very effective solution,” he said. “Although it’s no accident. The campus has taken a leadership role in seismic retrofit technology. They’re all earthquake junkies, so to speak.”
At Memorial Stadium, the sections directly on top of the fault will be cut into three large free-floating blocks. The blocks will be separated from the surrounding structure by 5 feet of open space, which will give the blocks room to wobble and twist — but not topple — in the event of an earthquake.
Steel, hinged flaps would prevent people from falling through the 5-foot gaps around the blocks.
The blocks would sit on plastic sheets unanchored to the soil, so when the earth moves, the blocks should stay put, more or less.
“The earth would slide past along that slippery surface,” Comartin said.
Below the plastic sheet, a series of stone columns will stabilize the soil, hopefully keeping shaking to a minimum.
“The blocks might twist and wiggle, but they should retain their structural integrity,” said Loring Wyllie, a structural engineer at Degenkolb Engineers in San Francisco who peer-reviewed Friedman’s plan. “It’ll be like a ship at sea. It might move a little, but the stadium’s a few inches off now anyway.”
The western half of the stadium will undergo a standard retrofit, with bracing, sheer walls and an extra layer of concrete coating the interior. The concrete will have breaks at either end over the fault, so if the stadium cracks, it will crack in a designated and relatively clean way.
The funds for the retrofit must be privately raised. The state Alquist-Priolo Act prohibits retrofit projects from costing more than half the value of the building, which could be a roadblock at Memorial Stadium.
The university values the stadium at $600 million, based on its replacement cost, but the valuation could end up in court if challenged by the plaintiffs in a recent battle over the adjacent athletic training center.