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 ...
I was in that business for about a decade. Structural grade bolts are subject to stringent requirements. In fact about 20 years ago cheap Chinese counterfeit bolts were the cause of a collapse in a shopping mall in St Louis IIRC.
Selling counterfeit or mismarked fasteners is now a Federal crime.
Thank you most kindly for your informative response.
You must be a youngster.
All I remember is 12,000 mile spark plugs, 20,000 mile brakes, and 20,000 mile tires.
A 100,000 mile car was a real outlier. Now that's the average car on the road.
I am an electroplater and metal finishing engineer.
I do not know of any plater in the USA with a 17’ oven. If the bolts are 147KSI in tensile or harder than RC32, they should have been baked for at least 4 hours before plating and a number of hours after plating. The post-plating bake is determined by hardness or tensile. I would have adjusted the bake for the thickness of the part since you have to bake the hydrogen out of the center.
The plater could have sent the parts out to a heat treater with a larger oven, but this has to be done quickly after plating before the hydrogen in the part has a chance to embrittle/damage the steel.
It is possible that the steel could have been embrittled by hydrogen before the parts got to the plater. Certain cutting oils can release hydrogen or it could have been pickled/de-scaled using acid which introduces hydrogen. However, the most common source of hydrogen is corrosion. Letting the raw stock rust is dangerous. After the hydrogen has done its embrittlement dirty work, the stock is ruined. You cannot fix it short of resmelting, reforging, re-heat treating, etc.
I have seen a lot of poor quality steel come through, some of it from U.S. mills, most from China.
As for testing, NASA and the military contractors have to do it, so why not the bridge builders?
This entire incident shows the need to have quality inspectors at every supplier down the line when you are dealing with life-critical parts.
When we built the Space Shuttles, we sent inspectors to the MINES to see where the ore came from and to take samples for the lab.
Let me see here...
“At least 30...”
of
“all 288 of the bolts on the new bridge”
Comes to somewhat over 10%, doesn’t it?
So...
“Caltrans insists the new span is safe...”
Suuuuure it is....
Seismic designs today are premised upon strength in ductility. Brittle failures were common in the Northridge quake, which changed many structural codes and design philosophies.
It might be something more fundamental like Min Gauge length or the distance the strain must be transmitted to the bolt for it to behave as a connector.
I wonder if the American factory hired illegal workers.
In any event, between these bolts and the Chinese-made parts, when the Big One hits, this sucker’s going into the water.
Better engineering and quality assurance management would have avoided this.
Good to catch it now, however.
The bolt weren’t specified well enough, in terms of strengths and/or tests were not made prior to installing said deficient parts.
Somewhere in the bureaucracy perhaps too much diversity trumped engineering & construction practices we used to handle fine.
Maybe the bolts came from a government ordered procurement from a minority owned supplier.
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