Memorial Stadium gets renovated with help from Berkeley’s own

BERKELEY – A massive renovation project at historic California Memorial Stadium is uniting the expertise of seismic engineers and campus experts to make sure that if the Big One strikes, Cal football fans and student-athletes are inside a safe, state-of-the-art and modern facility.

Design features of the stadium, which straddles the Hayward Fault, will include concrete “seismic blocks” at the end zones to keep fans from rocking as a quake rolls, a press box that can sway up to 12 inches in a large-scale temblor, and shock absorbers to prevent the box from crashing into the western seating bowl.

Everything except the outer wall and the eastern seating bowl of the nearly 90-year-old structure, designed by world-famous architect John Galen Howard to resemble the Roman Colosseum, is being rebuilt from the ground up. The renovated stadium is scheduled to reopen in fall 2012.

The novel design is a result of a unique blend of UC Berkeley researchers’ academic knowledge about earthquake effects and what to do about them, their extensive field experience, and the expertise of practicing engineering professionals hired to do the work.

“It’s a really marvelous solution that we can feel comfortable and safe with,” said UC Berkeley professor Jack Moehle, a member of the campus’s Seismic Review Committee.

“Cal is a stellar place in terms of how the collaboration works between this outstanding institution and professional practice,” said David Friedman, a UC Berkeley alumnus and a principal with the San Francisco firm Forell/Elsesser Engineers Inc., which did the structural engineering design.

Digging in together

Long before the $321 million renovation began, several members of the Seismic Review Committee met with the architects, HNTB Architecture and STUDIOS Architecture, and the engineers hired for the job. Composed mostly of UC Berkeley faculty members, the committee works on the seismic review of all campus buildings, including the new Student-Athlete High Performance Center adjacent to the stadium.

“The committee gets involved to bring forth the best science ideas, the best engineering solutions, and to let the engineers think about them,” said Moehle.

“It’s an honor to take your expertise in earthquake engineering and to use that to make sure that the campus and the State are getting the best design for their money,” added Jonathan Bray, professor of civil and environmental engineering and an expert on fault ruptures. Bray, civil engineering professor Nicholas Sitar, and Craig Comartin, campus seismic consultant, also are part of the stadium review team.

The project has been a rare opportunity to implement a combination of design elements that are tried-and-true, said Moehle, but have never before been used in combination in such a setting. “So, the collaboration between the review committee and the engineers was especially important here,” he said.

UC Berkeley hired an outside firm to dig extensive trenches and drill boreholes inside and outside the stadium, to provide data about the soil and rock underlying the old stadium, and to learn the extent of the fracture zone of the Hayward Fault.

The trenching and drilling confirmed that the fault has been slowly moving – a geological process called fault creep.  Over the past 90 years, creep produced a nine-inch gap in Section KK at the south end of the old stadium, cracks in the north tunnel, and offsets in pillars and supports under the now-demolished south end zone seats.

“Knowing where the fault is, you can then design a structure so it has a sliding gap where the fault will break, so the fault is allowed to move without damaging the structure,” Bray said.

These data on the fault helped the design team and the Seismic Review Committee members to settle together on design features including the concrete seismic blocks for the seating areas straddling the fault.

The new design: high-tech, common-sense

The final design divides the stadium into four pieces – north, south, east and west. The eastern seating bowl clustered around the student rooting section is sitting on solid ground and will remain largely untouched. But the western side will retain only the historic concrete façade. The new western bowl will be topped by a two-level press box – media, broadcast crews and game operations on the lower level, and members of the University Club on the upper.

“Though a ‘high tech’ solution, it is also a straight-forward and common-sense engineering solution,” said Friedman. “It will do a very good job of controlling the behavior of the structure to allow the fault to rupture without endangering life safety, which, of course, is our primary design criterion.”

Fans in the north and south end zones, atop two seismic blocks that will straddle the Hayward Fault, will find themselves taking a ride – but a safe one – if a quake strikes, as these blocks, enclosed on all sides, will slide, rotate and tilt with any fault movement.

Even in a 6.7 magnitude or larger quake that could cause the western side of the fault to slide six feet northward and drop up to two feet, the bunkers would remain intact, said René Vignos, principal structural engineer for the stadium project with Forell/Elsesser. A foot of clearance will allow the seismic blocks to slide without crashing into each other and protect the surrounding seating areas.

Forell/Elsesser seismic engineer René Vignos explains how the ground under the stadium’s south wall is supported in preparation for the construction of a new seating bowl. (Robert Sanders)

Under each block will be a four-foot-thick concrete mat, like a raft, sitting on two layers of high-density plastic sandwiched between layers of sand to facilitate sliding.

“One of the safest places to be in an earthquake is on top of a rigid block,” said Moehle, the T.Y. and Margaret Lin Professor of Engineering at UC Berkeley. “You could probably even push it back partially into alignment afterward. This is a very simple and elegant solution to a difficult problem.”

A dramatic press box

Another novel solution for the stadium involves the eye-catching, 300-foot-long press box. The curved, open-steel space frame incorporates cantilevered seats facing the stadium and a cantilevered upper level balcony with a glass floor off the back providing a priceless view of the bay.

“It’s going to be a very dramatic space,” Vignos said. Dramatic in an earthquake, too. The press box will be supported by four massive towers that will enclose the stairs and elevators. These concrete core towers will be vertically compressed by taut steel cables, providing internal stability to the concrete structure during a quake.

The press box projects above the top of the stadium seats and façade and can sway without hitting anything. The towers that support the press box, however, extend through the western seating bowl, and each has a gap around it at every floor, allowing the press box to sway independently of the seating bowl. To slow down the motion of the press box, several heavy-duty shock absorbers connect the towers to the bowl structure to damp out the motion from a quake.

If all goes as planned, the towers will be completed by early October, and then the press box, in five pieces, will be set into place by a massive crane – a dramatic feat.

When the stadium eventually reopens, its renovation will be “a real boost to the campus community,” said Moehle. The popular facility is used by several athletic teams, the Cal Marching Band and, in the summer, by sports camps. On game days, 63,000 fans will fill the seats.

“The stadium’s always been a wonderful place,” said Moehle, “Now, it’s going to be a state-of-the-art facility, the best place to go for a football game, with great views, the best athletics and, on top of that, it will be safe. Who could ask for more?”

The new facade and seating bowl will look like a restored antique, but brought up to modern standards to create a facilty that will significantly reduce seismic risk, and ensure life safety for the hundreds of thousands of fans who attend games every year.