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PA-NJ Turnpike Bridge Closed due to Fractured Steel Truss 6
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MikeHalloran
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Or, each particular portion of that particular member comprising an uncontrolled and undocumented plug weld and associated HAZ comprise an alloy puddle of uncontrolled and uneven composition, some of which may be cold short, i.e., brittle at the temperatures encountered over the river on the day the big bang was heard.
... Okay, I'm not completely happy with that above, so I'll try again:
Each of the plug welds was not documented, and likely not controlled wrt to electrode selection other than using what might have been available in the shop on very short notice without leaving a paper trail. The remainder of the bridge clearly has a DBT low enough to have survived a fair number of NJ/PA winters, but the plug welds in the failed member presumably have a DBT a bit higher than would be suitable.
If a brittle fracture starts in a localized area like that, will it be stopped when it propagates into a less brittle portion of the same member? Would the member have failed if there were only one mis-drilled hole? Should there be some sort of transition visible in the fracture surface as a fracture that started in brittle material reaches slightly less brittle material?
I hope they'll preserve the fractured ends for study.
It sounds like the sort of real-world problem that, e.g., AISC, should suggest as a research topic for someone. Those are probably not the only undocumented plug welds in standing riveted bridges.
Mike Halloran
Pembroke Pines, FL, USA
... Okay, I'm not completely happy with that above, so I'll try again:
Each of the plug welds was not documented, and likely not controlled wrt to electrode selection other than using what might have been available in the shop on very short notice without leaving a paper trail. The remainder of the bridge clearly has a DBT low enough to have survived a fair number of NJ/PA winters, but the plug welds in the failed member presumably have a DBT a bit higher than would be suitable.
If a brittle fracture starts in a localized area like that, will it be stopped when it propagates into a less brittle portion of the same member? Would the member have failed if there were only one mis-drilled hole? Should there be some sort of transition visible in the fracture surface as a fracture that started in brittle material reaches slightly less brittle material?
I hope they'll preserve the fractured ends for study.
It sounds like the sort of real-world problem that, e.g., AISC, should suggest as a research topic for someone. Those are probably not the only undocumented plug welds in standing riveted bridges.
Mike Halloran
Pembroke Pines, FL, USA
bridgebuster
Active member
My paper had this story
Link
Two quotes in the story by the Chief Engineer for the Pennsylvania Turnpike bother me:
[quote="It pretty much demonstrated a simple fact — that it's 1956 steel," ][/quote]
He should have qualified what he meant because there are people who will read it and think every 1950's era bridge is in danger.
Another statement that should have been qualified (bold text):
Someone will think they shouldn't cross a bridge on a cold day. Granted, a lay person knows nothing about brittle fracture but as engineers we have to keep in mind how we say things.
Link
Two quotes in the story by the Chief Engineer for the Pennsylvania Turnpike bother me:
[quote="It pretty much demonstrated a simple fact — that it's 1956 steel," ][/quote]
He should have qualified what he meant because there are people who will read it and think every 1950's era bridge is in danger.
Another statement that should have been qualified (bold text):
Someone will think they shouldn't cross a bridge on a cold day. Granted, a lay person knows nothing about brittle fracture but as engineers we have to keep in mind how we say things.
itsmoked... as noted in the information included above, hot short basically means that base steel in the heat affected zones of the weld become 'brittle' when the welded material cools. This can be caused by sulphur being in the original steel 'mix'. This brittleness can lead to a sudden failure of the steel because it has a greatly reduced ductility. Once the failure is initiated, due to the reduced steel section, failure continues and can proceed very rapidly/catastrophically.
Dik
Dik
dik; Thanks much, I learned a bunch on that sword article and see what you're saying.
Glad I took a material science course doing Charpy and yield tests and being taught what 'body centered cubic' was.
Keith Cress
kcress -
Glad I took a material science course doing Charpy and yield tests and being taught what 'body centered cubic' was.
Keith Cress
kcress -
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You are welcome guys,
I learned about hot shortening and cold shortening in Metallurgy class in Technical College. It actually took me a while to find that article that described what I had been taught.
B.E.
You are judged not by what you know, but by what you can do.
I learned about hot shortening and cold shortening in Metallurgy class in Technical College. It actually took me a while to find that article that described what I had been taught.
B.E.
You are judged not by what you know, but by what you can do.
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