Engineers to quake-proof Cal stadium on free-floating blocks

Published 26 September 2008

Engineers have solved one of the world’s great retrofit puzzles: how to keep UC Berkeley’s Memorial Stadium from crumbling into a pile of concrete rubble during a major earthquake

When Carole King sang “I feel the earth move under my feet / I feel the sky tumbling down …” she was probably singing about something more, er, personal than earthquakes, but a group of San Francisco engineers hope that those who happen to be at the University of California Berkeley’s Memorial Stadium during an earthquake will be able to use these words to describe their sensation (but without the “tumbling down” part). Seismic engineers apparently have solved one of the world’s great retrofit puzzles: how to keep Memorial Stadium from crumbling into a pile of concrete rubble during a major earthquake. The San Francisco Chronicle’ Carolyn Jones writes that 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, lead 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. “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.” Right through the end zones.

Memorial Stadium was built in 1923 atop the Hayward Fault, which the U.S. Geological 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 who might be 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 is 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 historical merit, which prevents 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. It is also the most perilous. The eastern half is built into the hillside and does not need to be retrofitted. The western half, though, 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. The model the university finally chose is notable for its simplicity, said independent structural engineer Craig Comartin, who sits on the campus’ Seismic Review Committee.