What Happened To the Bay Bridge? 407
farnsworth writes "Tony Alfrey has put together a fascinating page with some history, analysis, and possible explanations for what ultimately went wrong with the recent emergency repair of the San Francisco-Oakland Bay Bridge. The bridge has been closed for days and is not scheduled to open for days to come, hugely inconveniencing more than 250,000 people a day. His analysis touches on possibly poor welding, a possibly flawed temporary fix, and the absence of a long-term fix or adequate follow-up by Caltrans, the agency responsible for the bridge. Slashdot is a great engineering community; what other insights do you have on the bridge situation?"
Re:Lack of redundancy (Score:4, Informative)
There are four bridges running east/west over the bay, it just happens that there is only one in this particular (useful) location. Also, given that the Bay Bridge has to connect to Yerba Buena island, there's not really a lot of room for another one right next to it. So there is redundancy, but you have to deal with the physical realities of the area.
There *IS* redundancy. (Score:4, Informative)
People use other bridges and the bart.
To say there isn't redundancy, is simply silly.
Caltrans Says (Score:5, Informative)
The engineering authority in charge of the bridge and repairs already gave their answer to this on the morning news (yesterday, I think):
They found the crack. They designed the "band-aid": the saddle, T-bar, rods, etc. They had it fabricated and installed.
In subsequent days, they went back up to look at how it was doing. They found that it was vibrating more than they thought it should: it wasn't as rigid as it was designed to be. They recognized that this would lead to fatigue and failure.
They began designing the improved "band-aid" and planned to install it sometime in coming weeks.
To their surprise, *perhaps* related to unusually high winds, the system failed sooner than they thought it could.
The completed their improved design and are now installing it. (And they are counting their blessings that nobody was killed: they got lucky, that way.)
-t
Re:Lack of redundancy (Score:5, Informative)
Actually, they are currently building another bridge right next to it. These fixes are all to a structure that they hope to retire in a few years.
Re:My insight (Score:5, Informative)
The Oakland Bay Bridge isn't much of a landmark, really. In any case, it is *extremely* important to note that the western span of the Bay Bridge, which is a suspension bridge, is perfectly sound, as is the landmark (but less used) Golden Gate Bridge. All of these problems are with the eastern span, which is a cantilever bridge.
What happened indeed (Score:5, Informative)
Raids of Public Transportation Funds [transformca.org]
nearly $2.5 billion was diverted away from transportation programs [transportationca.com]
Re:Lack of redundancy (Score:5, Informative)
The Bay Bridge is not the only way from Oakland to San Francisco, there's the Richmond-San Rafael bridge to the North and San Mateo bridge to the south. There's also BART and various ferries and worst case scenario a trip through the South Bay and then up the peninsula. There's lots of ways into the city even if one of the bridges is out of service for some reason. The past two labor day weekends the Bay Bridge was shut down for repairs (the latest of which apparently caused the current problems).
The positioning of the Bay Bridge is limited by the layout of both San Francisco and Oakland. The Bay Bridge already spans one of the narrowest points between the cities and is bisected by Yerba Buena Island to reduce the effective length of the individual spans. There's nowhere else to really put another bridge in the area. There's no other spots with convenient freeway locations on both sides of the bay which would require whole new sections of freeways be build which means buying out a whole bunch of land that people already live on and a host of other problems. This construction would be in addition to building a whole new bridge.
Re:Lack of redundancy (Score:3, Informative)
Re:Lets see here... (Score:5, Informative)
"In 2003, Californians sent $50 billion more to Washington in federal taxes than the state received in federal expenditures. Representing a slight increase from levels that have held steady for three preceding years, the Golden State’s imbalance set a new record for any state, surpassing the previous mark (set also by California, in 2000 and 2001) of $48 billion."
http://www.calinst.org/pubs/balance2003.htm [calinst.org]
Maybe if that weren't the case, California wouldn't be so broke right now.
Closed for DAYS? Lucky California. (Score:4, Informative)
Re:Made in China (Score:3, Informative)
Re:Welders are a scapegoat (Score:5, Informative)
I strongly doubt that the welding is the culprit. "Faulty welding" doesn't happen on something of the scale of a bridge.
You're right on. If the author of the article would have watched any of the Caltrans news conferences, they would have answered some of his theories.
The weld that he claims failed was clearly described as only being tacked, not structurally welded. That weld wasn't supposed to hold the structure together, the tie rods were, which failed. One of the improvements they are making now is to replace the tacking with a structural weld, so that even if something broke, these pieces won't come apart. The other improvements center around reducing vibration, especially in the tie rods
Who wrote that article anyway? Some guy on the internet who looks at some pictures of the repair and thinks he knows what a bunch of engineers working on the problem didn't know?
Re:Meanwhile, in Segovia.... (Score:5, Informative)
You have no clue what you're taking about. Roman legionaries (who were paid) and paid laborers were used to build Roman infrastructure.
Re:Meanwhile, in Segovia.... (Score:2, Informative)
Roman Aqueducts were made of stone. The bridges in San Francisco were made of steel.
Stone erodes. This takes a long time. The erosion can be seen on the original stones in the aqueduct you mentionned. It is happening, slowly but surely, and eventually, if not properly maintained, the aqueduct will collapse. (parts of it have already collapsed, and been repaired... it's in the Wiki you linked, even.)
Steel corrodes. Unlike erosion, corrosion happens relatively quickly. Again, with proper maintenance, it can be mitigated, but it doesn't take long at all for it to become a significant issue. Like erosion, corrosion happens mostly on the surfaces, but water and other catalysts for erosion have a way of getting into cracks and crevasses, and eroding smaller things like bolts and rivets, which can't really be seen without taking the bridge apart.
When you can show me a way to build a mile-long suspension bridge out of stone, I'll be listening.
Wind usually not a problem. (Score:3, Informative)
It's surprising that they had trouble there. That's a big, stiff truss span, with lots of cross-bracing. Those usually don't have serious wind problems. (The Tay Bridge disaster [wikipedia.org] was, of course, one involving a truss bridge. But it was badly designed and very badly fabricated.) The worst case for wind is a long, narrow, thin span. The Tacoma Narrows Bridge collapsed through that kind of failure, and the Golden Gate Bridge was vulnerable to it. In 1951, during high winds, the Golden Gate Bridge deflected enough that one side of the roadbed was 11 feet higher than the other. Stiffening trusses [flickr.com] were added under the span. (These are big trusses, each over 20' high, but the bridge is so huge that few people noticed the retrofit.)
In the 1989 quake, the Bay Bridge had an upper deck section break at the joint between the high truss span and the lower spans. That was an impedance mismatch - the two sections oscillated in different ways, and the stress at the transition point was enough to break bolts. When the Bay Bridge was designed in the 1930s, those problems weren't well understood, and could not yet be simulated.
The problem seems to be that the quick fix for the crack was underdesigned. That was recognized within days, and a second fix was under construction.
The damaged eyebar could be replaced, but that requires fabricating a new eyebar and some specialized tooling to take off the load from that whole eyebar chain during repair. This span will be torn down in a few years, when the new span is finished, so that may not be worth it.
Re:Don't blame the three caltrans employees (Score:5, Informative)
Instead, they dump cones everywhere, dig holes everywhere, then quickly move on to the next site. Sure, you'll never actually see a CALTRANS guy working but it sure as hell looks like they must have a lot of people doing the work if they can dig up that much crap and have roadworks every couple of hundred yards.
Most highway work gets done at night. Late at night.
If you can figure it out, I have no doubt CA's dot.ca.gov website will show you where and when they're actively doing construction.
I drive around during the day and see cones.
I drive around at night and I see construction crews.
Re:Rushed (Score:4, Informative)
Things like this can't be rushed, plain and simple. Carefully executed planning is what's needed to take on these types of projects.
What XPeter said.
On the gripping hand, they should see if there's anything left of the civil engineering group from the old Hydro-Electric Commission in Tasmania. The collapse of the bridge over the Derwent River when the ore ship Lake Illawara collided with it was repaired by them when the department of roads weren't up to the task. The old Hydro took their sweet time to fix it, but fix it they did and it's better than new (ship-repelling caissons were added). The size and type of that bridge and the treachery of the waters within which they worked make them similar cases.
Re:Wrong audience (Score:5, Informative)
In interviews I've seen, the architects stated that the assumption was that any collision would involve a plane (specifically a 707) lost in the fog, flying slowly and trying to land. Such planes would not be fully loaded with fuel since they would be at the end of their trip, and they wouldn't be piloted by terrorists pegging the throttles at top speed.
The scenario envisioned was more like what happened to the bomber that hit Empire State building in 1945. It wasn't that big of a deal.
Re:Lets see here... (Score:4, Informative)
Re:MY insight, as an engineer (Score:2, Informative)
For starters, would you happen to know of any structural materials that can tolerate corrosion for that period?
Masonry - Many such bridges are hundreds of years old. Some are even thousands of years old!
Reinforced Concrete - Again, 100+ year old RC bridges are common.
Prestressed concrete - Not quite as old as some RC bridges, but again, 100+ year old examples are common.
Steel - Our Sydney Harbour bridge is 70+ years old. No it's not magical gold plated or ceramic, it's plain old steel with a sufficently robust anti-corrosive covering. It will be around for at least another hundred years.
I design structures, and I generally design them for 50 year design life. I don't like it, but it's the economic reality. Make no mistake about it, it's an economic contraint, not a physical contraint. If you don't provide a design solution that shifts costs onto future generations then the customer will find an alternate vendor who does.
Re:Wrong audience (Score:3, Informative)
I'm pulling from memory here, but I think that they did consider fuel. However, the planes today hold more fuel, they did not account for the missing (destroyed) fireproofing, they did not account for the furniture getting piled up in one area and concentrating the fire, and I don't think that they conceived that the inner wall would be breached.
Re:small (Score:5, Informative)
The situation in Afghanistan in 2001 was similar to the situation in Cambodia in 1970. Inside the capital of (Phnom Penh/Kabul), the (Royal Family/Taliban) ran things. Outside the city limits, the countryside was controlled by (the Khmer Rouge/various 2-bit warlords like the Northern Alliance). (The Royal Family/The Taliban) had effectively zero power and influence outside the capital.
The reason why bin-Laden was so far out in the boonies (couple hundred miles!!) in Afghanistan was, even the Taliban didn't like him. Pre-Soviet Invasion, he was just some radical kid with a big checkbook, nobody really important other than having close family ties with the Saudi royals. Even the mujahadim thought he was a nutball. His real influence? About as far as the distance between his pen and his checkbook. And of course when the US demanded the Taliban immediately turn over bin-Laden, the Taliban, having just enough police to clamp down on Kabul and about as much real military to provide a couple hours' target practice to the Northern Alliance, told the US they just couldn't do that. Not wouldn't, couldn't, as in, having no capability of doing a particular thing, in this case, handing bin Laden over. The US of course instantly informed the entire planet of the 'Afghani government's refusal to hand over bin-Laden. About the only people to really listen were inside the US. Everybody else already knew that 'Afghani government' is one of those contradiction in terms like 'military intelligence' and 'jumbo shrimp'.
Re:Wrong audience (Score:5, Informative)
During a botched takeoff, the first thing a pilot does is to begin dumping fuel as fast as he safely can. Jet fuel is similar to kerosene, which evaporates quickly in the atmosphere, usually before hitting the ground.
Most aircraft cannot survive a landing with fully-loaded fuel tanks (unless the plane itself is carrying an unusually light passenger/cargo load).
Also, the flight patterns around Newark, JFK, Teterboro, and LaGuardia would all avoid lower manhattan, even in the event of a severe failure or navigational obstacle. Odds are, they'd end up in the meadowlands, the hudson river, or a residential area. Briefly browsing takeoff-related aviation accidents around NYC seems to confirm this.
The odds of a fully-laden jumbo jet hitting a building in lower Manhattan by accident are close to nil.
Re:small (Score:2, Informative)
Let me introduce you to block grants. Sayeth the wik [wikipedia.org], "Since the 1980s, the United States government has provided large sums of money through block grants, under a policy that has come to be known as 'devolutionary' or 'new federalism.'"
Nope. Rural states have plenty of poor people receiving federal benefits, plus of course there are all those farm subsidies. Most "blue states" pay more in taxes then they receive in federal spending [taxfoundation.org]. It's the smaller, more rural states -- the "red states" -- that generally take more then they give. There are exceptions: D.C. and Maryland are quite "blue", but with the federal government right there of course a lot of federal spending happens. Still, the correlation is strong.