Posted on 03/27/2013 9:25:11 AM PDT by NormsRevenge
At least 30 of the giant bolts that hold together the new, $6.4 billion eastern span of the Bay Bridge have snapped.
As a result, Caltrans is considering replacing all 288 of the bolts on the new bridge before it opens, The Chronicle has learned.
Caltrans insists the new span is safe and that plans to open it the day after Labor Day are still on track.
However, officials say it's too early to determine how long it will take to fix the problem - or the cost.
Toll Bridge Program Manager Tony Anziano said engineers are "pretty confident" the problem with the bolts is not a design issue or a construction problem but related to the quality of the steel bolts themselves.
"This isn't exotic - this isn't some wild issue," Anziano said.
Unlike the Chinese-built deck sections, the bolts - some as long 17 as feet - were produced in the United States.
"It appears to be a type of materials problem - the presence of hydrogen in the metal," he said. The hydrogen makes the metal brittle.
(Excerpt) Read more at sfgate.com ...
This poster claims it is sheer insanity to spend millions of dollars on bolts and not QC them.
Bolts made in China?
Or thermal expansion. The longer a bolt is, the more it grows and shrinks in response to heating and cooling, and these were 17'.
Sounds like in the former Soviet Union....
The nail factory made their quotas every year....
increasing the size of the nails....(big ones are easier to make)
Ended up with a huge pile of 50cm long nails that nobody brought.
It is standard to bake the bolts at about 600f after plating to remove the hydrogen
May have been hard if they did not have a 18 foot long oven
Can be both. However design of bolt- or rivet-connected bridge spans is a very well known process. Bridges of this type were built for more than a hundred years, entirely without computers; all you need is printed tables. Steel made in China, on the other hand, with no quality control and no incoming inspection, is a very likely culprit. An engineer doesn't claim that "the steel has too much hydrogen" until he has the lab test results in hand.
A comment above mentions that some bolts were loose. If the holes are too large this can result in uneven loading of bolts - and then indeed some will be sheared off, and then the rest follows. If the bolts are not tight then they will experience axial stress instead of shear stress, and the thread will be torn off. It's all very obvious when you look at the bolt, and the guys who are investigating are usually experienced troubleshooters.
Caltrans insists the new span is safe...
I still distantly miss the beaches once in a great, great while.
About seven years ago, the oil field went through a period of buying Chinese drill pipe. Failure after failure after failure.
ASTM specs.
Not that hard to contract out. Friend of mine works in a place with an industrial oven several hundred feet long.
When you torque a bolt, even the toughest alloy, it stretches almost like a rubber band. It has to hold that state of tension without elongating beyond a certain point and loosening, or breaking, and it must hold this property over time. Design involves choosing the proper material for the expected load but sometimes the best calculations fail in practice.
The problem in California is not the bolts, it’s the nuts.
Considering what happened with the Nimitz Freeway pancaking during an earthquake, going above-and-beyond should be done in a place like San Francisco.
The reference to the pancaking of the Freeway was that the freeway had two layers. The earthquake caused the top layer to come down on the bottom layer. Some folks were crushed in their cars as a result, as I recall.
They will all fail, given time. You can extend the time but it will affect other considerations, appearance, cost, etc.
You could, and should, do a simple nondestructive hardness test on the material being used to make the bolts before the bolts are made and before any other test are done.
You could do a hardness test on enough material to make 288+ bolts in about 2 days max.
That would tell you if the material is up to specs before wasting any more time or money on it.
Too soft or too hard chunk it.
No point in spending any more time or money making a bolt when it’s going to be junk anyway.
You have to understand that this is a Cal Trans project, and Cal Trans is one of the most incompetent organizations within the State of California.
Several years ago in Orange County on a major freeway interchange where Cal Trans was in charge of constructing freeway “flyover” ramps, they discovered at a very late stage that the pre-stressed concrete was below acceptable quality. Initially they thought that the entire set of flyover ramps would have to be torn down. They finally found a way to “rework” them but it took nearly two years to do so.
In the case of this bridge, there was no excuse for both the general contractor and Cal Trans to have strength tests run on those bolts as well as all major steel components. But what the hay, this is California, and that just about says it all these days.
In the 70’s and 80’s it was American steel that was junk.
In one job alone I rejected over 1 million feet of 2 3/8” tubing.
When I’m “pretty sure”, and I often am, I check.
The GG Bridge was built in the early 1930's. In the 1980's, for the 50th year celebration, they allowed a mass of people to walk the bridge, completely filling it with people (jammed together weighing much more than any load of vehicular traffic). The bridge flattened out from it's arch but everything held together, and engineers were able to relax from their fear of a collapse (politicians wanted the people walk). That's 1930's U.S. steel! Nowadays, replacement steel pieces regularly break on the Oakland side of the Bay Bridge, some having damaged cars. Part of the reason for the new section.
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