Miami Pedestrian Bridge, Part IX 33

[JAE]

A continuation of our discussion of this failure. Best to read the other threads first to avoid rehashing things already discussed.

Part I
thread815-436595

Part II
thread815-436699

Part III
thread815-436802

Part IV
thread815-436924

Part V
thread815-437029

Part VI
thread815-438451

Part VII
thread815-438966

Part VIII
thread815-440072


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[FortyYearsExperience]

https://www.youtube.com/watch?v=HjSvH9QLbkk

This youtube posting is most revealing. Go to minute 37:23. Linda Figg pronounces that "It's all post tensioned concrete, . . . so everything is in compression."

As the poet said, "A little learning is a dangerous thing. . . " And yet, because we know that Linda Figg is not an engineer, she must have picked this idea up from an engineer on the team.

 

[TheGreenLama]

Common practice for design of post-tensioned concrete box girder bridges is to size concrete cross-section, PT, and cable drape such that concrete section always remains in compression due to axial and bending stresses.

 

[Ingenuity]

And yet, because we know that Linda Figg is not an engineer, she must have picked this idea up from an engineer on the team.

I am not sure if you are being facetious. If not, according to her Linked In profile she graduated from Auburn University in 1981 with a BS Civil Engineering, Structural.

 

[Settingsun]

37yearsexperience

 

[jrs_87]

If anyone is interested, you can view history of hokie66 and FortyYearsExperience (view history by clicking their handle) debating force terms: tensile, compression, shear, and moments. I do not know why it is such a touchy subject. Call me strange, but I enjoy the banter. Actually, there are no such forces, only 42 from which everything else is derived. So when forty years becomes 42, all will be enlighted.

https://en.wikipedia.org/wiki/42_(number)

 

[FortyYearsExperience]

Common practice for design of post-tensioned concrete box girder bridges . . . such that concrete section always remains in compression due to axial and bending stresses.

Funny how huge tensile cracks showed up in the FIU bridge's concrete deck directly after being loaded up under gravity. Also, funny how the FIU bridge is not a box girder bridge.

. . . according to her Linked In profile she graduated from Auburn University in 1981 with a BS Civil Engineering, Structural

Funny how Linda Figg cannot place a licensed Professional Engineer ("PE") qualification behind her name. This is a professional certification/licensing requirement in every state for a person selling professional engineering services to the public. Funny how the investigation has not touched on this point.

 

[BridgeSmith]

Funny how Linda Figg cannot place a licensed Professional Engineer ("PE") qualification behind her name.

As the owner of a multi-billion dollar engineering firm, she's obviously far too busy to design anything, so she likely let her license expire. She wasn't the designer for the FIU bridge, so what licenses she holds or held is irrelevant. Her firm has plenty of licensed engineers to do the actual engineering work, which is obviously all that is required in the states where Figg has designed bridges (which is the majority).

Edit: "They [Figg] have built and managed bridges in 42 states and six countries..." Link If there was a requirement that the owner of the engineering firm be licensed to practice engineering in those 42 states, then you can be sure she'd be licensed in those states.

 

[FortyYearsExperience]

so she likely let her license expire.

Funny how a search of the Florida database on Professional Engineers in the historical record of the state shows that she was never licensed. Although, the record does show her father was licensed, deceased in 2003. See below.

Also, funny that, without a professional license, she is heard selling to the public why the bridge is safe because "everything is in compression" -- when clearly that was false information. The point I made, above, is that somebody on the design team with a PE license clearly believed the same thing and fed her that false information.

Now, who on the record from the design team believed that the bridge was safe against all tensile forces? Could it be that the last minute frenzied tensioning of the steel cables in diagonal #11 was motivated by the belief that "more pretension in the steel cables" would put "more compression into the failing concrete." ? Seems like the investigation has gone silent on simple questions like this.

 

[BridgeSmith]

Making a sales pitch doesn't require a PE. Obviously, owning an engineering firm doesn't either; neither does commenting in general terms about a design, I believe.

...a search of the Florida database on Professional Engineers in the historical record of the state shows that she was never licensed.

Did you check the registration lists in the other 49 states and the dozens of other countries that license engineers? Just because she wasn't licensed in Florida, doesn't mean she wasn't licensed. Anyway, it's still irrelevant, as there's no requirement that the owner of an engineering firm be a licensed PE.

 

[jrs_87]

I recommend this book:

https://play.google.com/store/books/details?id=BAzhV4drMsUC&pcampaignid=books_web_aboutlink

Bridges: The science and art of the world's most inspiring structures
David Blockley
February 25, 2010
OUP Oxford

It is written by an engineer, is non-technical but does a good job acknowledging human challenges in bridge building. The chapters on history are very well done. This book is applicable to this thread, however, his writing style for this audience is sure to draw flaming attacks.

 

[BridgeSmith]

BTW, the audio linked and quoted above was recorded in 2015 - well before the design was done. So, the assertion that "she is heard selling to the public why the bridge is safe because "everything is in compression" -- when clearly that was false information." and the speculation that "she must have picked this idea up from an engineer on the team." are also a false assumptions.

 

[samwise753]

Whie I agree with HotRod that her license status is not really relevant to her owning a compnay, it does sound really off for her to say "it's all in compression" when it clearly is and was not. She's representing an engineering firm that specializes in high-level bridge design, so she really needs to know better what she's talking about.

Back to the collapse though. I did a Google search to see if a beam with an open truss-frame web was ever looked at before, and I came across some research done on a beam of this type to be used for a roof. I haven't delved into too deeply yet, but it seems they had a lot of trouble dealing with the force concentrations where the struts met the flanges. They're section was also symmetrical about the midline, and they used consistent strut angles through out. They also had full prismatic sections for the 1st and last quarter (roughly) of the beam. The most telling (and obvious) statement of the paper was:

"The fact that concrete does not work efficiently in resisting tensile stress makes it very
difficult to design a truss made of solely reinforced concrete."

https://digitalcommons.unl.edu/cgi/...redir=1&article=1013&context=constructiondiss

 

[jrs_87]

Here is a concrete truss type that indicates designer was concerned about tying members to deck.

 

[WinelandV]

jrs_87,

In that picture, tying to the deck is important, but that's not what's driving the increase in section as the post approaches the deck. Underneath the deck, at the posts, you can see a beam underneath. This is a "half-through pony truss", otherwise known as a "handrail truss" in my neck of the woods. While the posts and diagonals obviously brace the top chord at the panel points for buckling in the vertical direction, the posts rely on a moment connection with the beams under the deck to provide the out of plane bracing for the top chord (if SlideRule is still reading this thread, I imagine that he will see the obvious need to use Engesser's solution). So, any aggressive tying in to the deck is really a by-product of the posts tying in to the beams underneath.

Really, the deck is spanning between the beams underneath. There's really not going to be the crazy force transfer between the posts/diagonals and the deck as there was in Miami.

At any rate, that is a really cool looking bridge. Were you able to find a location for it?

 

[BridgeSmith]

Obviously as it ended up, in the FIU bridge, the concrete was not all in compression, which contributed to its failure. As designed, the concrete in post-tensioned and prestressed structures is usually supposed to stay in compression. On the occasions where tension occurs in the concrete, it is incidental and not included in the load resistance of the member.

 

[hokie66]

I'm travelling for a few months, so haven't been monitoring this discussion. But just wanted to respond to Ingenuity's facetious comment about me perhaps masquerading as someone else. Not true, but funny. As to the concept of "shear friction", I still don't believe it is well thought out, but have said that many times...

It looks like a lot of people here still can't see the forest for the trees. A bridge built with concrete, even in the form we associate with a truss, inevitably acts as a frame, with all the attendant moments involved.

 

[jrs_87]

winelandv Re "Pony Bridge"

https://historicbridges.org/bridges/browser/?bridgebrowser=california/kilburnroadbridge/

Here it is, in California no less. It is actually a steel truss later encased in concrete.

Posters, question, EOR stated "strut" cracks would be repaired (with epoxy?). Is this yet another questionable assertion from Figg? What good would epoxy do in such a highly loaded member? And the second those deep cracks formed, did Linda Figg's promise of 150 year life span become undeliverable even if the bridge did not fall?

 

[jrs_87]

Brand new high-tech bridge collapse in Canada for which cause will never be found.

https://pressfrom.info/ca/news/cana...pses-hours-after-opening-in-saskatchewan.html

"the bridge was built to Canadian standards"

 

[3DDave]

"The Reeve of the rural municipality (RM) of Clayton says the bridge that collapsed six hours after it opened was built without having geotechnical investigation done on the riverbed it stood on. A bridge building expert calls that approach "irregular." "

https://www.cbc.ca/news/canada/sask...ech-investigation-of-riverbed-reeve-1.4829890

Considering all the elements of the bridge remained unfractured, I'd say it sank.

"You can't drill through water," he said. "You can't do it. You can't take underground samples." (politician Hicks)

James Eads would like a word slipped in on that. His bridge which still stands on the bedrock below the muddy bottom of the Mississippi.

https://en.wikipedia.org/wiki/Eads_Bridge

Looks like they are chasing leads on other bridges done in a similar way -

https://www.cbc.ca/news/canada/sask...t-collapsed-bridge-new-restrictions-1.5087229

 

[jrs_87]

3DDave, Re: Canada Bridge
Upon further research, I have found this collapse to have extreme political overtones, like the FIU bridge.

Local politicians wanted to use inexpensive screw (helical) piles. Defend decision post collapse claiming no proof more expensive structure would have not failed as well.

https://www.cbc.ca/news/canada/sask...g-provincial-cash-for-better-bridge-1.4859394

Helical Piles

http://helicalpilebook.com/Files/Ch_01.pdf

(I'm probably starting to diverge off topic too much.)