PA-NJ Turnpike Bridge Closed due to Fractured Steel Truss 6

[milanov]

http://www.app.com/story/news/traff...3/cracked-nj-pa-bridge-means-delays/96973694/

Engineers will need at least two weeks to get a handle on the repairs required to fix a heavily traveled bridge between Pennsylvania and New Jersey after one of its steel supports fractured cleanly into two pieces, a highly unusual event that had some experts suspecting a flawed, 6-decade-old weld....

http://www.philly.com/philly/busine...ne-off---or-a-hint-of-a-systemic-problem.html

Engineers working on the closed Delaware River Bridge face the task of determining whether a failed beam was an isolated case or something that could happen elsewhere on the structure.

“They’d be interested in knowing if this is a systemic issue,” said Carl DeFebo Jr., spokesman for the Pennsylvania Turnpike Commission.

The crack completely sheared through a truss beneath....

 

[Lomarandil]

Arguably, this is a better location for it... but there's a parallel thread here:

http://www.eng-tips.com/viewthread.cfm?qid=420024

 

[JAE]

Here's the fracture:

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[msquared48]

JAE:

I see what appears to be two horizontal pins in the end of the broken face. each at the third points and centered.

Seems strange...

Mike McCann, PE, SE (WA)

 

[JoshPlumSE]

Those may be the plug welds referred to in the other thread.

 

[djs]

I may be all wet but it looks to like the inside face of the crack is rusted. That would indicate that the crack had been present for some time.

 

[msquared48]

Shear failure in a compression member resulting in brittle fracture from cyclical loading at plug weld locations, welding that crystalized and strain hardened the local mild steel matrix.

Interesting...

Mike McCann, PE, SE (WA)

 

[JedClampett]

That thing broke clean through. Different member, different time and a bunch of people could of been killed.
I consider this a fortunate occurrence in a way.

 

[hokie66]

Freshly painted, so I think the crack is new. And it looks like a tension member, continuous top chord near support. The member is, I think, a wide flange, and we see the outside flange. Maybe all the way through, but not conclusive from the photo.

 

[JAE]

Saw this from two days ago in a news report:

Officials say the 14-inch truss below the westbound lanes cracked suddenly, causing the bridge to sink slightly. It’s not clear when the steel fractured. Scientists with Lehigh University are working to determine the cause and extent of damage.

Karl Frank, professor emeritus of engineering at the University of Texas at Austin, told the Inquirer that, decades ago, workers may have accidentally drilled holes into the bridge’s steel beams and filled them with plug welds, which could have led to the fracture. It’s a quick fix typical of repair work in the 1950’s (the bridge opened in 1956), he said, but something that engineers would avoid doing today."

Here's another overall photo of the fractured wide flange (W14 I think)

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[JAE]

And some repair work underway:

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[appot]

workers may have accidentally drilled holes...and filled them with plug welds...It’s a quick fix...but something that engineers would avoid doing today

How would a hole in a steel beam be fixed today?

I would think fillet welds around a plate plus a plug weld. Is he saying that they only did the plug weld?

 

[JAE]

appot - don't know the answer to that. I think perhaps leaving the hole would be just as bad as the weld infill but maybe not in terms of fatigue.

AISC's Table A-3.1, section 1.4 kicks you into Stress Category C for holes while section 8.3 and 8.4 (plug welds) imply a Stress Category E or F, respectively.

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[msquared48]

I believe the recommended fix is just to fill the hole with a bolt and nut.

Mike McCann, PE, SE (WA)

 

[dik]

They might want to check the sulphur content of the steel... to see if potential for hot short brittle fracture.

Dik

 

[BridgeEI]

Mike is right. In the bridge world we put a bolt in the hole and tension it.

 

[bridgebuster]

A brief report from FHWA.

 

[JAE]

Here's a couple of photos from bridgebuster's linked report and it included the statement:

[blue]Based on the length of time from when the failure is presumed to have occurred to when it was discovered, and the bridge’s continued performance under full live load during that period, it is unlikely that the bridge was in immediate jeopardy of loss of stability. It is clear that the fractured member was carrying no load, and the structure had redistributed the load to stable load paths. It is unlikely that the load paths would suddenly change such that the fractured member would again be relied upon for any load carrying capacity, without restoring the original truss geometry. However, the immediate splice plate repair was necessary to provide the owners and consultants with a level of comfort with the safety of workers accessing the bridge. [/blue]

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[milanov]

http://www.burlingtoncountytimes.co...cle_9167da59-68ea-5ab4-8cca-a9dcd2495370.html

 

[swall]

That is a brittle fracture--no shear lips present at the fracture periphery. I bet it made a pretty good bang when it went.