If you drive on the new Bay Bridge's east span after it opens in 2013, you will be safer because of an innovative bridge piece designed to flex, bend and break so the main structure does not in a big earthquake.
Once the inevitable Big One finishes shaking the Bay Area, Caltrans crews can replace any broken fuses to restore the bridge to full strength — much like an electrician replaces a fuse that blows out.
The $6.3 billion east span from Oakland to Treasure Island is the first bridge to use the breakable metal fuses for added protection against earthquakes, Caltrans officials said Monday during a tour for media members that was tied to Saturday's 20th anniversary of the Loma Prieta earthquake.
The 1989 temblor collapsed a section of the upper deck of east span, one of the searing images of the disaster. While the span reopened a month later, state officials decided they needed to replace the structure — 53 years old at the time of the quake — with a new bridge that is now going up just north of the existing one.
"We have several innovations in the east span that have been not be used in a bridge before," Caltrans spokesman Bart Ney said. "Scientists continue to learn more from earthquakes. We're taking advantage of that."
The breakable metal fuses — metal rods — will be used in two places. They will protect the skyway, a 1.2-mile-long already complete bridge deck built on piers, and the self-anchored self-suspension bridge, the yet-to-be built tower that designers say will give the bridge an elegant appearance.
In the skyway, the fuses are built in the center of metal beams that can move back and forth in a sleeve when an earthquake moves the bridge decks.
"The fuses in the hinge pipe beams absorb the motion, taking the stress off the rest of the structure," Ney said. "We can come in fairly quickly after an earthquake and replace the fuses."
A similar application of fuses will be used in the construction of the four metal legs that will support the 525-foot-tall tower of the self-anchored suspension bridge.
Metal pipes called shear link beams will connect the four tower legs, and fuses within those beams will absorb the brunt of shaking to prevent damage to the tower, Ney said.
"All bridges move during an earthquake. The challenge is how to minimize the damage," he said.
Despite all the seismic safety measures, the Bay Bridge is expected to sustain some minor damage after a major earthquake on the San Andreas or Hayward faults. However, Caltrans expects the damage to be minimal enough that the region's most heavily used bridge can be back in operation within a short time — perhaps a day or two — first to emergency vehicles, and then to regular car traffic.
"I would feel safe on the bridge during an earthquake," Ney said. "I would feel safe with my children there."
Reach Denis Cuff at 925-943-8267. Read the Capricious Commuter blog at www.ibabuzz.com/transportation.
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