May 24, 2011
Image Slide Show
By Evan Aczon
Contractors and architects are accustomed to racking up shipping charges and sending massive data files of plans and blueprints to experts around the country for structural advice. It takes a lot of patience, and often both sides would be better off if they could visit face to face.
Fortunately for those working on maximizing the structural integrity of Cal's Memorial Stadium, in-person meetings are not only possible, but unavoidable. That's because those same experts who have built their careers studying the activity of the Earth's tectonic plates have probably spent a Saturday or two cheering on the Golden Bears from the stands.
The Berkeley Seismological Laboratory is one of the top labs in the world, mostly because of its proximity to two of the more active faults in the United States, the San Andreas and Hayward faults. In 1922, John Galen Howard and the University decided to construct Memorial Stadium with the latter fault running right through the middle.
"How do you deal with faults? What do people know about dealing with faults?" said Rene Vignos, the project manager for Forell/Elsesser Engineers. "We're fortunate that in Berkeley, the best experts in that field are professors here. We have to bring our design in front of them to be reviewed."
Granted, seismology wasn't the most exact science back when the stadium was built, and the positioning of the stadium in relation to campus took precedence over what may have been going on beneath the Earth's surface.
Given the evidence gathered over the 89 years that Memorial Stadium has been in existence, tectonic activity can no longer be denied. That's made the stadium project a top priority on campus and was also why the project was so meticulous in its undertaking.
Recent major disasters have brought the structural integrity of buildings in high-risk zones into the spotlight. Damage to the freeways in San Francisco and Northridge, the Superdome in New Orleans and metropolitan areas in Japan have shown that planning for the worst can make a difference.
This is the aspect that architects, such as Darryl Roberson of STUDIOS Architecture, have been working on for the better half of the past decade.
"The objective of the engineering is life safety, not limiting damage to the building." said Roberson. "The objective is to save lives so there's no collapse or big failure. In a huge earthquake, the building can deform, but it should stay intact."
Seismology, and therefore structural design, has come a long way in the past 90 years. Because of the development of technologies and their use at the Berkeley lab, the innovations in structural research are paramount in the design of the new stadium.
One of the most important realizations is that building on a fault can be done safely. The stadium, as it is now, is not structurally sound, but it was not necessary to relocate the stadium because of its proximity to the fault. In fact, research has shown that structural damage sustained a few feet from a fault rupture is very similar to the damage incurred over a mile away.
The Hayward Fault runs through both end zones at a diagonal, crossing through the west corner of the south end zone to the east corner of the north. With that in mind, Vignos shared the secret to the success of the new design: moving parts.
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."
All of the simulations done in the lab found that an earthquake would in fact cause these wedges to rotate. The layers of sand and HDPE plastic would provide a flat surface for them to rotate on. Since there is a gap between the wedges and the bowl sections, the worst damage would be at the corners and would be minimal at those points.
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.
When completed, the stadium will be safer than ever. With all the improvements, the stadium will still shake, rattle and roll in the event of a tectonic shift. But most importantly, the separate sections, along with the fans inside them, will all still be in one piece.
