August 13, 2007 2:11 PM PDT

A seismic shift for San Francisco Bay Bridge

A seismic shift for San Francisco Bay Bridge
Related Stories

Road Trip 2007: Science and tech in the Southwest

August 14, 2007
Related Blogs

Home at last


August 10, 2007
OAKLAND, Calif.--On October 17, 1989, I was sitting in my dorm room at the University of California, Santa Cruz, about to watch Game 3 of the World Series, when it suddenly felt like someone was slamming an 18-wheeler into the building.

It turned out, of course, that it wasn't a truck but rather the Loma Prieta earthquake, a 7.1 temblor that killed dozens of people in the Bay Area and caused a section of the eastern span of the San Francisco-Oakland Bay Bridge to collapse.

In the years that followed, there was a lot of hand-wringing about the seismic safety of the Bay Bridge, the Golden Gate Bridge and many others in the area. And as a result, starting in the 1990s, it was decided that the eastern span of the Bay Bridge needed to be replaced.

After a lot of public discussion and debate, the powers that be chose an innovative design for the project: A 525-foot, self-anchored suspension (SAS) bridge that, upon its expected completion in 2013, would be the world's largest such span.

A self-anchored suspension bridge is one that, instead of having the main cable anchored down into the ground, has the main cable anchored to the roadway itself. The theory, in this case, is that by anchoring the cable to the roadway, it will strengthen the entire construction and, hopefully, stand up to a large earthquake.

For most people who live in the Bay Area, the sight of the construction that followed has been a regular component of the drive from Oakland into San Francisco, though the view of the work, off the north side of the bridge, is stunted at best.

So, as the last stop on Road Trip 2007, I dropped in on Bart Ney, the public information officer assigned to the bridge project for Caltrans (California's transportation public works organization), and got a personal tour of the construction, including a boat ride out to where workers are laying the foundation for the SAS section.

Click for gallery

And as someone who loves bridges, I have to say, this was quite a treat. I had been wanting to get a close-up look at the work for a long time, but since I don't have a boat, and you can't really see much of the work being done when you drive across the existing Bay Bridge, this was the first opportunity I've ever had to get a sense of what's really happening.

For example, I didn't even know until the boat got close to the construction that the new skyway is actually two different roadways, one for eastbound traffic, and one for westbound. And it will be comprised of four separate sections, only one of which uses the SAS approach.

One thing I remembered about the process of getting the construction going was that several years ago, when the final design was still up in the air, there were several roadblocks standing in the way of the SAS approach. First, some were concerned that such a design wouldn't be seismically safe in an area where it is virtually certain that there will be at least one major earthquake within 30 years. Second, there were major budget worries, especially since the expected cost of the bridge, if done with SAS, would come out at $5.487 billion.

Click here to Play

Video: Labor Day bridge makeover
The busy Bay Bridge will be closed as a portion of its eastern span is destroyed. Renderings help explain.

Ney told me that Caltrans administration initially didn't want to go with SAS. Instead, they wanted a giant skyway.

But "that didn't take into consideration what would work best for this area aesthetically," Ney said.

Indeed. The fact is, the project incorporating the SAS section will be one of the world's great bridges, and easily a worthy counterpart to the glorious and famous western side of the Bay Bridge, which connects San Francisco to Treasure Island. Even better, it will be visible largely from the East Bay, an area that tends to get short shrift in great civil engineering projects.

Ney explained that the SAS section's main cable will begin on the eastern side of the bridge, extend up to its tower and then down to its western end, go underneath the roadway, wrap around, head back up to the tower, and then back down again to the opposite side of the bridge from where it begins. The theory is that this creates tension across the entire span of the SAS section that is self-reinforcing and will then be strengthened against an earthquake.

He also pointed out that no known construction method is guaranteed to hold up against a major quake, but that the SAS design is thought to be as strong as any other approach, and therefore should serve the Bay Area well.

Road Trip 2007 promo

One reason for that, Ney explained, is that there are several points along the bridge construction that are intentionally designed to take the force of a big quake. The idea is to direct the force of a quake to these areas specifically because, if they fail, they can be easily repaired without the bridge collapsing or suffering catastrophic damage, as recently happened in Minneapolis.

One such application of this method, Ney explained, is the use of what are called "shear link beams" in the SAS tower, which is really four separate pillars linked together. The shear link beams are designed to move independently of each other in a quake, and can be unbolted and repaired if necessary.

Similarly, the west end of the SAS section has what are known as isolation casings, the largest such casings in the world, Ney said, which are big holes cut out around the columns coming up from the SAS section's foundation. Because the casings are not tied to the soil itself, they can move in an earthquake.

One other example of this design methodology is the use of hinge pipe beams, which connect the eastern skyway section of the bridge to the SAS section. It's sort of like two large dowels, the inside joints of which are designed to allow for some parallel movement in a quake. The hinge pipe beams are actually 60 feet long and 6 inches in diameter. At the beams' center is a "fuse" that can bend in a quake.

"So if the bridge starts moving," Ney said, "that's the weak link. We can replace the fuses with new ones and get the bridge going" again quickly.

As part of my tour, Ney took me out on a boat and we circled around the western end of the new construction. This was great. We moved slowly around the bridge's different sections, coming to a halt right where the new skyway--which will connect to the SAS section--ends, and where the SAS section itself will be built.

There, on a barge, are 13 "gazebos" inside of which the SAS foundation is being created. This is done through 13 "piles," each of which is 10 feet in diameter and 200 feet deep. I couldn't see inside, but I imagined peering down into the depths of the bay.

After this, we turned around and began our trip back towards the Caltrans dock on the eastern side of the bridge. But first, we had to stop and check out what is surely the money shot of the construction.

There, with the existing eastern side of the bridge on one side, the curved double-skyway sits majestically with the East Bay area behind it and the bay in the foreground. For someone who loves bridges, this was a view for all time.

See more CNET content tagged:
SAS Institute, span, roadway, construction, bridge

3 comments

Join the conversation!
Add your comment
Original numbers
When the original plan to replace the bridge was funded under
AB 1171 in 2001, the completion date was to be this year at a
total cost of around $1.3 billion. The added complexity of
including the SAS component, instead of the recommended
continuation of the skyway, has more than quadrupled the
original costs. And, the new budget doesn't include what
Caltrans calls "program contingencies". Still, it's pretty
impressive and I'm looking forward to my first crossing, even
though it may be a decade from now.
Posted by imoretti (5 comments )
Reply Link Flag
2013?
If you start from the beginning of construction of the Golden Gate, to end of the construction of the Bay Bridge, it took less time than for these clowns today to build a little span. <shakes head>

By the time they finish (and this is if it's in 2013) it will have been nearly 25 years since Loma Prieta.

Yeah, America is still a "can do" nation. <rolls eyes>
Posted by anarchyreigns (299 comments )
Reply Link Flag
Earth's Purging
The recent earthquake in Peru got me to thinking about something. I'll say this up front, I'm not in a good mood today, so this will probably not be a peachy piece of writing. So, if you are one of those people who only wants to hear positive things, probably best you go away.

Up until very recently, I belonged to the group of people who said that we humans had very little effect on the planet, on the environment, on nature. Well, I've changed my position, mostly after I began to think about the natural disasters throughout history. Are these happenings coincidence, or the result of cause and effect?

There have been diseases that have killed millions, there has been, and still is famine that kills millions, there are severe earthquakes that have killed thousands in just a few minutes, hurricanes and tornadoes, the killer tsunami that killed all those people in Thailand in 2004, the list goes on.

All this being said, I believe that in this life, some things, well, most things, are random, BUT, on the other hand, there are many things that are not. There is this thing called cause and effect - I am a big believer in cause and effect. I also believe that our planet is a living thing and has a life force of its own. This fact is not as glaringly obvious as it might be in some other living organisms, but if you look closely, you'll see undeniable evidence that the earth does, after all, have a life force of its own.

In recent history, we've seen examples of all of the things I mentioned above. In all the locations where these "disasters" have happened, there is and has been some very bad energy circulating the area. What got me to thinking about this was, I spent the last 15 months in Lima, Peru. I just moved back to the U.S. a couple of weeks ago, so I wasn't there for the earthquake. Well, I'll tell you from first hand experience, something is dreadfully wrong with the general population there. The selfish, rude, filthy attitude of the majority of people there is beyond belief - much worse than anywhere else I've ever been. The nasty energy just sits in the air there. I don't feel the need to go into all the gory details, you'll just have to take my word for it for now. If ever you do, though, get the opportunity to visit Lima, please do it so you can see for yourself. Granted, the quake didn't take a lot of human lives - not this time, anyway, but if I'm right about this, it's only a matter of time before something similar to the Indian Ocean tsunami of last year happens in Peru - well, in lots of other places for that matter.

So, where do we stand in America? We had the quake in San Francisco in 89, we've had tornadoes ripping through places where they normally inhabit, but we've also had them in places where it's not normal for them to happen, we had Katrina last year. AIDS, cancer, and other dreaded diseases are running rampant right under our noses. Auto accidents have killed more people than all the wars in the history of man - and cars have been around for HOW long - a hundred years or so (the car thing is more cause and effect than earth's purging)? Keep in mind that we humans are only using a tiny fraction of the space on the planet - in fact, if you took every human on the planet and gave them a square yard to stand in, you could fit them all in a space half the size of New Hampshire (I did the math myself). BUT, with all that area on the planet that has no people on it, how many natural disasters (hurricanes, tornadoes, earthquakes, tsunamis) occur in uninhabited areas? Yes, there are scientific facts that can explain away why these occurrences happen in highly populated areas, but how did those scientific facts become scientific facts? In other words, was it a coincidence that the 89 San Francisco quake happened close enough to the city to have caused all that damage? Do we know about any major earthquakes hitting uninhabited areas? There is all that California coastline that is very lightly inhabited - why did it not hit those places instead of the highly populated San Francisco area? Was it a coincidence that Katrina blasted the highly populated, underwater city of New Orleans head on? The giant tsunami that hit Thailand - coincidence that it hit where it killed thousands?

How many of you out there think that it's normal to contract cancer, or AIDS, or any of the dreaded diseases that are killing humans by the millions every year? How many think that it's normal for millions of people in Africa to starve to death? How many think it's normal for people to be murdering each other? There are direct causes for every one of these horrible tragedies. The scary thing is, the attitudes of humans in general are not good - never have been, and the result is, the bad energy circulates and causes these killer occurrences. Inherent greed, gross selfishness, and just general bad thoughts and intentions - all contributing to the premature loss of human life.

Well, this brings me to my sad assessment of the human race as a whole. I believe that humans are not good by nature. My proof is, watch just about any kid - he or she will spend much of their time seeing what they can get away with, and very little time seeing what good they can do. As a person gets older, these tendencies become somewhat under control, but the intentions are still there. Someone came up with the idea of a "Higher Power" that we all must answer to - in order to try to keep people from completely being evil, and it seemed to work for a while, but it appears that it is losing its effect. No, not positive thoughts or beliefs, but as I always say, reality is not always pretty.

So, what's the answer? I have no answer. If magically, people's attitudes change for the better, then great, we would all have a much better world to live in, but I don't foresee that happening. Denial, or reality, you choose.

ParadoxianGiant
Posted by ParadoxianGiant (5 comments )
Reply Link Flag
 

Join the conversation

Add your comment

The posting of advertisements, profanity, or personal attacks is prohibited. Click here to review our Terms of Use.

What's Hot

Discussions

Shared

RSS Feeds

Add headlines from CNET News to your homepage or feedreader.