Salesforce Transit Center closes due to cracked support beam 16

[hpaircraft]

Salesforce Transit Center closes due to cracked support beam

Not exactly a failure yet, but not a good start, either.

 

[dik]

No pictures... steel beam, not concrete... no yielding? possible brittle fracture from some triaxial condition... don't know, not enough information.

Dik

 

[human909]

Roof beam supporting the roof garden.. Who knows at this stage. Possibly a major error in calculating roof loads.... Possibly just cheap steel.. Possibly not a 'crack' at all because reporting this type of thing is notoriously poor.

 

[JohnRBaker]

Perhaps it's some of that Chinese steel that was left-over from when they were doing that Oakland Bay Bridge upgrade a few years ago:

Dang: The Chinese-Made Bay Bridge Continues to Fall Apart

http://www.americanmanufacturing.or...inese-made-bay-bridge-continues-to-fall-apart

Structural work on Bay Bridge complete, but questions remain about subpar steel

https://www.mercurynews.com/2017/08...lete-but-questions-remain-about-subpar-steel/

John R. Baker, P.E. (ret)
EX-Product 'Evangelist'
Irvine, CA
Siemens PLM:
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The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[dik]

Apparently, the steel was 'merican made...

Dik

 

[Pete_K]

From another article

"...said the crack was found near a weld on a stress-bearing horizontal beam. He said he did not know how long the crack was, but he told reporters that American steel was used in the center’s construction."

 

[JStephen]

My guess: welding problems.

 

[MintJulep]

Or weld joint detail that didn't consider fatigue due to springiness of the span.

 

[ldeem]

The article linked in the original post calls it a 6' tall beam. Assuming that is correct it must be a deep plate girder. I wonder if its a flange to web weld? It will be interesting to see pictures when they come out.

 

[dik]

said the crack was found near a weld on a stress-bearing horizontal beam

Didn't know where the crack started. That's what made me think of a tri-axial condition initiating a brittle failure.

Dik

 

[BridgeSmith]

What we've seen most often with that size plate girders is poor connection details that result in rigid restraint in corners (such as a stiffener welded to a flange and web without clipping the corner of the stiffener), leading to massively high stress concentrations. Don't know if it's anything of the sort here, since currently have no information about where the crack, if it even is a crack, is located. At this point, we can only offer wild speculation.

 

[epoxybot]

Wider inspection has discovered a second cracked beam. The beams are in an area that appears to be part of the terminal that spans Fremont Street. What side of Fremont St. is not yet known. SalesForce Tower is on one side of Fremont St, and Millennium Tower is on the other. News: Link
Locale:
Link
Link


Crack 1:
Link

Crack 2: With Fireproofing
Link

Skanska won the Steel Supply & Erection Contract.
Link

Steel Erection crossing Fremont Street
Link

Miscellaneous Steel Erection Photos:
Link
Link
Link

Adjacent to Millennium Project
Link

 

[ImminentCollapse]

epoxybot,
Are you the mayor, chief engineer, attorney general, chief of police and head librarian for San Francisco by chance? Star for you again.

Concerning crack for certain, looks like stiffener/web/flange interface origination as HotRod10 speculated.

IC

 

[human909]

That is a scary looking crack. How much life is left in that beam if the tension flange is gone....


Regarding fatigue cracks around welded stiffeners:

"Approximately 96 percent of the number of cycles to failure were consumed in growing the crack through the thickness of the flange. This was confirmed by visual observations of
a number of beams. The remaining 4 percent of the life was spent in propagating the crack across the flange width and into the web."

 

[JAE]

human909
Is that the beam in question or is that just an example of a cracked beam?

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[bimr]

Is that the beam in question or is that just an example of a cracked beam?

JAE, refer to epoxybot's post and links @ 27 Sep 18 00:50.

 

[dik]

another link:

https://www.on-sitemag.com/construc...ce=482&utm_medium=email&utm_campaign=180926AQ

 

[ldeem]

It looks like a lot weld in that section so may be weld shrinkage cracks? The area close to the weld would have reduced fatigue allowable as well but the structure isn't that old so it doesn't seem like a roof area would get a lot of high cyclic loading.

I reminds me of a torn clip angle I saw recently. I can't be sure but I think the tear happened when the structure experienced a shock load from an explosion in another part of the structure. I wonder if there was some shock to the tower? Maybe a dropped load of material?

Finally, one article mentioned the same crack at two beams – so maybe bad detail at the connection resulting in high weld shrinkage stresses. If that is the problem they would need to make some remedial repair to every location with the detail.

 

[dik]

Ideem: see the second post in this thread... too soon for fatigue...

Dik

 

[JAE]

bimr - thanks...I was just too lazy to look at the links I think.

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