Miami Pedestrian Bridge, Part VII 51

[JAE]

A continuation of our discussion of this failure. Best to read the other threads first.

Part I
thread815-436595
Part II
thread815-436699
Part III
thread815-436802
Part IV
thread815-436924
Part V
thread815-437029
Part VI
thread815-438451




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[3DDave]

Greenlama,

The base of 11/12 could be pushed from the deck. The distance from the base of 11/12 to 10/11 is greater than the horizontal distance spanned by 11. As 11 rotates it has to push 11/12 as it aligns with the 1-10 canopy span. The main factor limiting the push is that it is also being subject to a side load, which imposes moment loads at both ends, causing the rupture of the concrete at both ends. Once the joint passes over-center it then pulls the deck and the canopy-12-remains of 11 triangle off the pier.

 

[bimr]

I disagree. There are vastly more non-licensed engineers in the US than licensed ones, probably by multiple orders of magnitude.

Yes, but that is not true when working on engineering design projects for the government where all of your work will be stamped. Civil engineers represent the vast majority (about 70 percent) of licensed professional engineers.

FIGG is an engineering design firm, not a contractor. How would you do project management in an engineering design firm without a PE? Project management in an engineering design firm is supervising PE's preparing specifications and drawings.

The principal (PE is required) of the engineering firm is in charge of the project work, making key decisions and an unlicensed owner would have to defer to the principal.

The fact of the matter is that it is not that difficult to obtain a PE license.

It does not make any sense not to pursue a PE license when your career goal is working for an engineering design firm doing government projects.

When you are selling your engineering design services, you present yourself as a PE.

 

[JAE]

bimr,
I checked with the Florida requirements. Some states require ALL the firm owners/principals to be PE's. Some don't and Florida does not require all to be PE's

Project management in an engineering design firm is supervising PE's preparing specifications and drawings.

Not necessarily - project management, where it is supervising the schedules, tasks, timing, resources,etc. of a project is not necessarily "engineering".
If the PM was making or forcing technical engineering decisions then yes, that would be practicing engineering.
But scheduling project milestones and other such "management" is not engineering.

When you are selling your engineering design services, you present yourself as a PE.

I think there is a difference between an individual engineer selling their services as a licensed professional vs. a large firm like Figg, having a marketing person, or a non-PE principal, selling THE FIRM's engineering services.

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[TheGreenLama]

3DDave,

I agree that 11 can push 12 out, but to do that the 10-11-canopy node must move downwards. For that to happen hinging is occurring nearby in canopy as well as bottom slab. Top of pier is a fixed point, and 10-11-canopy node is a fixed vertical line of descent. In other words, failure has already begun. It was mentioned way back somewhere in this thread that only a small horizontal shear movement at 11-12 base (or along sides of 12 within diaphragm) would lead to catastrophic cascading series of events. Maybe this is what happened: slight movement as horizontal restraining force was removed due to shear failure, followed by massive load redistribution that leads to hinging and collapse.

 

[Stephen Nuchia]

"to get a PE one basically has to find a job working under the supervision of a PE for a significant period of time" yes, that's the main pipeline and for good reason. I happen to have spent most of my career working solo on software so while I passed the POE I never had enough documented PE-supervised time to get a license. But most state still have the "grandfather clauses" on the books. When the laws were written there had to be a way to bootstrap the licensed population so there are provisions for obtaining a license other than by supervised work. I know a non-degreed licensed engineer who did that, I worked for him before he got his license and I applaud both him and his state board for the move. But it is and should be rare.

 

[jrs87]

TheGreenLama is correct, very small movement of 11 lead to collapse. This is counter-intuitive. What allowed for movement is unknown to us at this point. Once 11 moved (or its confinement moved) over a certain tiny threshold the bridge became a machine. No longer static, so now in the discipline of mechanical engineers.

The amount of motion required is proportal to the elasticity of the structure. Here the truss works against the stability of the bridge because its overall ridgedness, combined with 11 not being confined, locally concentrated energy to member 10. Then the 950 ton lever-hinge-parallelogram machine proceeded to wreak destruction. The failure of 11 was very brittle, hence very little deflection before bursting.

All illustrations I see show 11/deck shear motion as large, i.e. Polish youtuber. The best way to understand collapse (not cause) is to just assume 11 is cleanly removed in an instant. This reproduces mechanism of collapse (but not the root cause of failure) :

https://www.youtube.com/watch?v=9pkLhbuS5cU

Truss theory and behavior is actually very involved and something very few understand fully. P.S. Strictly speaking, in technical terms calling this overall structure a truss is a misnomer. But individual sections of it are truss-like. All of this means this one-off design has to scrutinized from scratch and empirically tested.

Ms Figg video reminded me of Feng-shui and Numerology. That's unfortunate. Was March 10 move date based on newspaper Horoscope?

 

[jrs87]

Not about FIU, but interesting bonus material:

http://whlcarchitecture.com/projects/river-center-branch-library-baton-rouge

http://www.theadvocate.com/baton_rouge/news/article_aa9ba804-436c-11e8-a08c-5b653c197b97.html

http://www.theadvocate.com/baton_rouge/news/article_4b56cb6e-4ca2-11e8-94b2-f3c6818e2ea6.html

http://www.theadvocate.com/baton_rouge/news/article_3e2510f0-6835-11e8-bd76-13772bdb038b.html

http://www.jotdown.es/2016/07/la-pasarela-del-pajaro-cachondo/

 

[chris snyder]

It was mentioned way back somewhere in this thread that only a small horizontal shear movement at 11-12 base (or along sides of 12 within diaphragm) would lead to catastrophic cascading series of events. Maybe this is what happened: slight movement as horizontal restraining force was removed due to shear failure, followed by massive load redistribution that leads to hinging and collapse.

Now I understand what you meant by ~"this wouldn't happen unless #11 got longer"
#10/11 drops a bit just before collapse, which is why this man theorizes shearing at #11/12/deck wasn't the cause. He explains/stops it at 13:50.

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

I think I see the surviving worker (Carlos Chapman) to left of the crane boom. Looks like he's crouched down several frames before #10/11 moves, then see his helmet move up likely when he latched his harness. This video can be single-stepped (from ~0:24).

https://www.youtube.com/watch?v=_o019WWA77U

The ZLD slo-mo doesn't show this/him as well (somewhere said this has additional processing - I assume it's the same video).

This might be the referenced post about a minor shift in #11/12 causing catastrophic failure.

https://www.eng-tips.com/viewthread.cfm?qid=437029

29 Apr 18 02:27

Since concrete failure only needs .003/inch compression for failure, the amount #11 would need to slide across deck is only 8" x .003" = .024", Or for a visual, the equivalent of 7 sheets of 20# printer paper. Result, .025 travel = 8,000 psi to fillet = explosion.

Much I don't understand there, but I get the idea.. once a break starts, the whole span comes down.
This after the photos came out (though prestressing was done before the cracks appeared - removing shoring triggered cracks).

https://www.eng-tips.com/viewthread.cfm?qid=438451

2 May 18 03:42

The cracking evidence is that the bottom of #11 slid across the deck, while the lower (4" tall?) side was being held back by a stirrup. Then they prestressed #11 to 560kips, & transported. The next step would place the bridge on pier with full 2,000 kips load at small 1/2 size #11 fillet block. #12 held tight, & #11 slid to crush small undersized fillet. The #4 pict crack is probably 2x the .024" travel I figured was needed to explode fillet.

I'm curious if they didn't tighten #11 rods beyond 560 kips to try to close cracks. The span survived moving with 560, though de-stressing rods (joint would move a bit), then re-stressing (to 560) may have had other effects.

Diagram shows pulverized area (with klugey fix to hold joint..). Cutterhead said "explode" twice and I wonder if this could be literal. Odd that #11 rebar at top of pier isn't bent and duct is still intact (some spalling on #12 as #11 rode up, but I suspect ~half of #11 was off to east side), and the PVC tubes in the deck didn't break up (though one cracked).

This using Meerkat's post and his input data

https://www.eng-tips.com/viewthread.cfm?qid=436802

22 Mar 18 12:04
shows end of #12 (with canopy held at right angle, hinged at #10/11) would move about 6 ft north before it starts moving back, which agreed with an estimate from slo-mo video (only about 2 ft can be seen). A bit odd that pier on north side shows no spalling at top edge - seems #12 was on the diaphram which didn't fall until rotation was almost finished. The "no shear" video at 10:25 cites only one piece of rebar bent on top of pier north of #12.

A better image after collapse using old-school (2nd-grade..) technology. Shows about 20% of #11 chopped by canopy - from video and photos, the canopy broke at north end of blister (a dark spot appears on side of canopy in frame after "worker latches up"). The piece of wire represents lower PT rod - shows about 7 ft of unbroken PT rod would come out.

 

[jrs87]

chris snyder,

Your old-school cutout method is actually commentable.

When all the math on this design is rechecked, it may come back that the triangles in the truss where too large for the behavior of the thin deck and canopy. A Baltimore, X, or double stacked truss may have been better. In addition it should have had two inline truss systems running down the middle. Same or similar total cross-section and weight, just two seperated. Most importantly, the end members could have massive sear walls since they are near pier and would not add that much moment. The pier should be larger too. In the end they stuck with ABC and faux stays, so 11 had to be thin.

This case in textbook example of designers painting themselves into a corner.

 

[bimr]

I think there is a difference between an individual engineer selling their services as a licensed professional vs. a large firm like Figg, having a marketing person, or a non-PE principal, selling THE FIRM's engineering services.

I researched the issues discussed prior to posting them. According to Florida regulations, don't believe that you can have a "non-PE Principal". I also don't believe that it is accurate to describe Figg as a "large firm" either. While Figg Engineering is a privately held firm which limits the available public information, sources have estimated the annual revenue as $14.3 million with 105 employees. The marketing at similar firms of this size is usually done by the management, which is why a PE is useful.

"Figg Engineering Group is located in Tallahassee, Florida. This organization primarily operates in the Civil Engineering business / industry within the Engineering, Accounting, Research, and Management Services sector. This organization has been operating for approximately 29 years. Figg Engineering Group is estimated to generate $14.3 million in annual revenues, and employs approximately 15 people at this headquarters location and 105 total employees across all locations."

The revenue to Figg Engineering from the FIU work is probably in the range of $1 million.

I would describe Figg Engineering as a boutique firm, an organization that provides specialized services for a particular segment of the market.

As someone that has worked for several engineering firms whose business consists of providing government services, my opinion is that it very odd that Ms. Figg (who has a civil engineering degree) never obtained a PE. At the firms that I have worked for that provided engineering services to the government market, the only management employees that were not licensed were employees that went to unaccredited educational institutions and could not obtain a license.

 

[JAE]

bimr,
You don't believe "that you can have a non-PE Principal" in Florida yet I just posted off their website (see table above) that they only require "at least one person" to be a PE.

Is it weird to have non-licensed principals? Yes, somewhat, but many firms have unique leadership/management structures...mine included.
We do work in Florida and have a non-licensed partner in our firm so I know you can do it.




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[TheGreenLama]

chris snyder,

Reading thru your most recent post it's amazing how much of this thread I've already forgotten.

I've never done any forensic engineering before. It feels odd, as if I'm tailoring my answer to fit the observations. Kind of like having the answers to a test before you take it. But maybe that's what forensic engineering is.

Here's a possible sequence of events at joint 11-12 based on observed cracks, and the little we know, borrowing heavily from earlier posts. Cracks noted sequentially by numbers. It's a good story. Whether it bears any resemblance to reality is an open question:
1) Observed crack prior to move, a result of dead load. Story should have ended here. Remedial action should have been taken (if possible?), or bridge destroyed and begun anew. Maybe stressing of temporary PT in 11 partially closed crack; maybe it did nothing other than give a false sense of security.
2) Move occurred. PT rods destressed. Crack reappeared. Temporary PT in 11 was now called on to close crack and save bridge. Assume both PT rods are stressed, possibly above what was done in 1. Tensile cracks may begin to appear behind top PT bar anchor plate.
3) With no dedicated confinement steel in front of anchor plates tensile forces acting perpendicular to the PT rods cause crack to propagate. Dead load also continues to work on crack. Shape and depth of crack beneath 11-12 indeterminate. Two things conspire to separate the top PT anchorage from the slab. Shear force from 11 now pushes horizontally against top rod, and PT force acting on top anchor plate will initially want to pull it upwards. Pictures show a very neat cavity between the nearly undamaged PVC pipes on either side of 12 within the diaphragm, possibly the result of top anchor plate bursting, or shear, or a combination, so crack at deck surface would fall inside of PVC pipes. Stress in top PT bar now goes to zero. Axial load in 11 now generates shear failure along this 1-2-3 plane. This begins collapse sequence. More on this below.
4) Slight movement along 1-2-3 plane causes load redistribution, resulting in hinging at various locations. Hinge points are top canopy, bottom of 11, top of 11, bottom slab, and even base of 12, with the order possibly being as noted. With the tremendous loads acting here, there's no reason to believe 11 would remain attached to 12 for long.
5) Bottom PT rod is torn out as 11 rotates and slides out.
6) Face of 12 is ground away, partially from 11, and partially as it slides downwards and outwards along back edge of diaphragm, once bridge has fallen far enough for 11 to push it beyond diaphragm.

Questions:
--What is the horizontal movement necessary along the 1-2-3 plane before collapse sequence and hinging is initiated? mm or cm? Because bottom PT bar remains attached to slab we're probably only talking mm's.
--Why does bottom PT rod remain in slab? It's sort of obvious when looking at the picture, but still unsure.
--Neither mild steel chevrons placed in deck slab, nor placing longitudinal PT along the centerline of bridge, would have likely prevented this potential failure mechanism from happening as crack 3 could also progress along top of slab to near top anchor plate. Plausible?

 

[bimr]

bimr,
You don't believe "that you can have a non-PE Principal" in Florida yet I just posted off their website (see table above) that they only require "at least one person" to be a PE.

Is it weird to have non-licensed principals? Yes, somewhat, but many firms have unique leadership/management structures...mine included.
We do work in Florida and have a non-licensed partner in our firm so I know you can do it.

Here is a more detailed explanation. I was referring to the Principal (officer of the business) listed on the Certificate of Authorization of which there can be only one Principal. By the way, the referenced table appears to be copied off the Harbor Compliance website, not the FBPE.

Of course there may be more principals as part of the firm ownership. However, Florida requires the other principals to be subordinate to the one Principal officer of the firm that is listed on the Certificate of Authorization.

Here is the application:

Application

Here are the paragraphs:

"Please list the name, business title, Florida PE license number and address of the professional engineer who is the principal officer of the business."

"If the PE named as a principal officer is not named as the President, Vice President, Secretary or Treasurer of the Corporation, or Limited Liability Company (LLC), then the application must be accompanied by documentation from the entity’s charter or bylaws which provides the title of the officer and that the PE named as such officer is empowered to bind the corporation or LLC in all of its activities which fall within the definition of the practice of engineering as that term is defined in Section 471.005(7), F.S."

The other point that I made is that if the owner is not the principal officer of the firm, then it may be an awkward situation where the owner is working under the direction of the principal officer of the business.

Also, I did not say it was weird which implies something supernatural or uncanny. I posted that it was odd which is defined as unusual as engineering firms do not have great career paths for non-engineers.

 

[JAE]

bimr
Thanks for the clarification.


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[chris snyder]

TheGreenLama, I like the sequence - especially the crack pattern. Will think on it more.

I must be wrong about #11 walking up #12 and going east... only 2 pieces of rebar on that side of #12 are slightly bent.

I still wonder if the #11/12/deck joint (brittle concrete?) could literally explode. About 4 ft are gone from the bottom of #11. I can imagine it breaking apart (as did #3), but that area is pulverized like dynamite blew it apart... it would take LOT of concentrated energy to do that.

I looked some, but didn't see much reinforcement/rebar in the blisters or canopy. Neither looks very strong (shouldn't have to be), but there wouldn't be much holding the #10/11/canopy joint together. #10/11 blister popped off, and #9 diagonal punched through.

#11's upper rod anchor plate bugs me - more after reading your crack sequence. This is spec'd at 8"x12" for a 1.75" rod, but it looks ~8" square (~same as the jack's plate).

 

[SwinnyGG]

The other point that I made is that if the owner is not the principal officer of the firm, then it may be an awkward situation where the owner is working under the direction of the principal officer of the business.

'authority to bind the corporation' just means authority to enter into contracts.

Our purchasing department enters into contracts a couple dozen times a day, every day- that does not mean that the CEO works for the purchasing agents.

 

[jrs87]

Mr. Kenneth Jessell, FIU senior vice president for finance and administration and chief financial officer

QUOTE:

“We wanted it to be from the very beginning a signature bridge, because we could’ve easily put in a box bridge…just to get across. We wanted it to be a continuation of the City of Sweetwater and FIU,” said Jessell. “I’m pretty excited about it.”

http://panthernow.com/2016/02/22/new-bridge-to-benefit-student-pedestrians/

 

[bimr]

'authority to bind the corporation' just means authority to enter into contracts.

Our purchasing department enters into contracts a couple dozen times a day, every day- that does not mean that the CEO works for the purchasing agents.

Here is the passage from the application with emphasis added:

"If the PE named as a principal officer is not named as the President, Vice President, Secretary or Treasurer of the Corporation, or Limited Liability Company (LLC), then the application must be accompanied by documentation from the entity’s charter or bylaws which provides the title of the officer and that the PE named as such officer is empowered to bind the corporation or LLC in all of its activities which fall within the definition of the practice of engineering as that term is defined in Section 471.005(7), F.S."

Application

It appears that you are quoting out of context since defining the 3 page application with just the words 'authority to bind the corporation' is foolhardy.

"Quoting out of context (sometimes referred to as contextomy or quote mining) is an informal fallacy and a type of false attribution in which a passage is removed from its surrounding matter in such a way as to distort its intended meaning."

quoting out of context

In this matter, I doubt whether you can find an attorney that will agree with your context as there is little obscurity in the words. In fact, if you review the rest of the entire application, you will find the following:

"This application must be signed by the qualifying engineer in order to process your Certificate of Authorization application.

As the principal officer of this business organization, I understand that I remain personally liable for negligence, misconduct or wrongful acts which I may commit. In addition, I will be responsible for all such negligent acts, wrongful acts, or misconduct commit ted by any person under my direct supervision or control, while rendering professional services on behalf of the business organization. Except as provided in s,558.0035, F.S., the fact that a licensed engineer practices through a business organization does not relieve the licensee from personal liability for negligence, misconduct, or wrongful acts commit ted by him or her.

_______________________________
Signature and License # of Professional Engineer acting on behalf of business"

Even one with full confidence in their own abilities would have to pause before taking responsibility for the acts of hundreds of other employees. That is why the Principal PE is empowered to bind the corporation in all of its activities which fall within the definition of the practice of engineering as that term is defined in Section 471.005(7), F.S..

Some say the ability to quote out of context is not worth much. However, with the skill to quote out of context and an additional 65 cents, one can obtain a senior coffee over at McDonalds.

 

[SwinnyGG]

I wasn't directly quoting anything... 'authority to bind' is a well-defined legal term with a clear definition. This is L1 level discussion.

'authority to bind' means authority to enter into contracts on behalf of the corporate entity. That's it. You will not find a lawyer admitted to any bar in the United States who disagrees with this definition.

Legal Dictionary: Bind

There is a lot of other content in that document you keep linking- but what you're arguing hinges on the phrase "that the PE named as such officer is empowered to bind the corporation or LLC in all of its activities which fall within the definition of the practice of engineering"

The layman's terms version of that Florida requirement is:

"At least one officer of the corporate entity must posses a valid Florida PE license and must be legally capable of entering into contracts on behalf of the same corporate entity, per the corporation's bylaws and/or structure."

Just because an employee of a company is authorized to enter into contracts on behalf of that company does not mean that owners of that company now work for that person, or now have to work under their direction.

Let me quote you out of context:

there is little obscurity in the words.

You can be condescending until your fingers turn blue, if you want. It doesn't make you correct.

 

[dik]

'authority to bind' simply means that he has signing authoruty.

Dik