SAN FRANCISCO (CBS) – It’s the most expensive public works project in California’s history. Every day, 280-thousand cars thump over the reason it all began. It’s at pier E9 where the cantilever meets the incline section. Little do commuters know, they’re rolling over the reason for spending $6 billion.
Back in 1989, the bridge that was designed to withstand a repeat of the 1906 quake was knocked out of service by a quake that was only 3-percent as powerful. It caused serious damage to the bridge and caused part of the upper deck on the east side to collapse onto the deck below.
Commuters might be asking, what’s going to stop the new bridge from falling down? Caltrans bridge engineer Doctor Brian Moroney answers that:
“Why is the bridge not gonna fall down? Because we thought about seismic right from the beginning. I have never made an important decision on this job without my seismologist sitting in the room and my geotechnical engineer,” Moroney said.
Crews are sinking the world’s longest self-anchored suspension span into some of the deepest mud on earth.
According to Moroney, “The soil conditions out on this bridge, it’s the poster child of poor soils, and we’ve had to incorporate that into the design.”
Engineers also took the Hayward Fault into account as well as the Rodger Creek Fault.
“Both are major players in the Bay Area in terms of past and future earthquake activity,” said David Schartz of the U.S. Geological Survey. “Our estimate of the magnitude if both went at once is 7.2 to 7.3. That’s really large. We really haven’t had an earthquake of that size in a modern American City,” said Schartz.
When it snaps, the bridge will react like any other bridge. There will be movement in the superstructure. The cables will bounce around and the cars will feel it. But one thing should happen that didn’t happen before – you will still be able to drive across it.
The roadbed is supported by 160 concrete filled steel piles battered as much as 300 feet deep. Also, seismic shock absorbers act like cushions between the four central towers. They’re called shear link beams and they are designed to absorb the shock of a quake.
And that’s not all, 20 extraordinary hinge-pipe beams absorb the energy of a quake and might get damaged, but the adjoining bridge segments should survive. In short, the new bridge should be usable after the big one.