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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[bimr]

jgKRI (Mechanical)

There you go again.

Providing free legal services in the form of a cliff notes version where you can shorten a 3 page legal requirement into just 3 words. Incredible, and probably made without even reading it. You must have the best experience.

I am really honored frankly to have played such a big role in hopefully, hopefully, getting rid of this issue. We have to look at it, we have to see is it real, is it proper, what's on it, but I hope it checks out beautifully. I am really proud, I am really honored.

Lacking experience working as a professional engineer, it seems that you fail to understand that unlike non-professionals, or individuals whose trades do not require licensure, licensed professionals are deemed to have duties independent of their contracts. The difference between an ordinary contractual duty and professional duty is that professional engineers owe the client an independent duty imposed by law, namely the duty to exercise the skill and knowledge normally possessed by engineers in good standing in similar communities.

That is the reasoning behind the state's act spelling out the requirements for certification of authorization for engineering services. That is why the state requires a single principal officer of the business. If you still fail to understand the issue, talk to an attorney.

 

[SFCharlie]

truss diagonals into the bottom slab and top canopy terminate in a "J" bend

In the photo at the end of chris snyder's (Electrical) post above at 25 May 18 20:18
the lower "J" bend in #11 is leaning intact against the top of the pier.
from this I'm guessing that part of the deck exploded along with the ends #11 and #12.
I don't know what that implies about the order of events, but could the PT rod have crushed the deck and bottom of #11?
Thanks

 

[SwinnyGG]

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

Right... that's the (only) point I'm making.

licensed professionals are deemed to have duties independent of their contracts. The difference between an ordinary contractual duty and professional duty is that professional engineers owe the client an independent duty imposed by law, namely the duty to exercise the skill and knowledge normally possessed by engineers in good standing in similar communities.

This statement is absolutely true. I've yet to make an argument that disagrees with it.

shorten a 3 page legal requirement into just 3 words

That 3 page legal document lists 11 requirements. I simplified exactly one of them, and stated that in my post. Maybe you didn't read it. I don't really know.

Either way, you're now concocting some type of strawman argument about the whole set of requirements when the only part that's really of interest is the one I originally quoted in my last post. I would post a snarky link with the definition of 'strawman' but you've already been condescending enough in this thread for both of us.

If it's ok with you, maybe we can go back to talking about concrete now.

 

[TheGreenLama]

SFCharlie,

According to drawing B-97 the those J-bars (7-S03) extend into the diagonals 5'-9". The bar visible in the photo looks like a side bar from 11, with the top bars resting on top of pier. They look surprisingly straight. The bottom bars near the bottom PT anchor are still in the deck. The fact that the J is still intact demonstrates the isolating effect of using that type of bend to try and anchor the diagonals into the slab. Beyond that I'm not sure.

Because they are so straight might imply there was NO explosion of 11's base. If 11's base exploded prior to 12 being dislodged you'd expect to see deformation in the J-bars, as 11 would've been rammed into 12. The fact that they're straight could mean that 11-12 moved laterally more or less together, with the base of 11 being ground away by 12 only after 12 became separated and slid downwards and outwards. Hard to say.

 

[chris snyder]

Rebar was running the length of #12 (spec of lower area above at 21 May 18 21:37) and likely held #12 together across the cold joint as (I suspect) #12 broke loose at the top of the upper anchor plate (in photo above at 21 May 18 18:40) along crack 6 where it meets crack 2 above (6 Jun 18 21:21).

Speculation... lower end of #11 moved north a bit as #11's lower PT rod was tightened and triggered events - #12 slid down and north, the weak #10/11/canopy connection broke/dropped/hinged, pushing down on upper end of #11 while bottom of #11 hinged toward the deck and PRIED the cage out of the deck, causing the lower end of #11/deck to explode from leveraged tension on the connection (and leaving the PVC tubes ~intact).

Probably need to draw/cut it out, but if #12 was off the north end of diaphragm, and #11 was "laying" on the deck east of #12, the lower end of #11 may not have touched #12 (spalling on south side of #12 from diaphragm instead of #11??)... need to consider only two rods perpendicular to east edge/along #12 are bent a bit, while rod/duct/rebar exposed from bottom of #11 appears intact. Both would have been "laid easy" on top of the pier when the diaphragm slipped off the pier late during north end events.

 

[epoxybot]

chris snyder - Finally, someone else ponders if #11 was pried from the deck. I have been trying to work this out for some time.

Just to stir the pot, ask yourselves if there is more of #11 missing from below the canopy than from the #11/12 node? To my eye it appears there is more missing from the canopy end of #11.

 

[MOJOJOHN]

Respectfully,

Rather than prying at the bottom of #11, I suggest that the sudden explosive failure of the dead end of diagonal #11 at the base may be due to an dead end anchor failure. We can see in the photographs that there appears to be a lack of any type of confining reinforcement in the local zone of the anchor in the Polish blow up of the video. I would have expected to see spirals or some sort of confining ties that remained after the failure, wrapped around the pt bar and duct. Possibly some voids behind the anchor to contribute to weakness? The much discussed shear, cold joint and cracking all could have contributed to this the failure.

Remember, the anchor details in the local zone are by the PT supplier, so we have not seen them yet.

The anchor plate does also look small, not 8 x 12 as specified, but this is hard to tell from the photograph. I calculated about 1 3/4" thickness for the plate with 45 ksi steel, which looks about right for the threaded bar and nuts.

The cleanness of the bars and pt suggest an sudden failure under great force (280 kip released suddenly, maybe another 280 kips right behind it in the top pt bar.)

After the anchor failure, the lightly reinforced #11 diagonal, with no shear reinforcing and minimal column reinforcing failed catastrophically. The member was also designed for compression only with little room left for moment that may have occurred due to uneven pt force at failure.

With member 11 gone, member 10 went from tension to small compression (only local, not truss forces) and member 9 remained a compression member putting its full force on the deck which was no longer a truss, but a beam to the north and sudden and total failure occurs.

Respectfully submitted

 

[3DDave]

Prying on #11 can't really happen until very far into the collapse. A feature to note is that the deck was clean of #11 even though there should be a lot of rebar in place. If #11 was pried loose those rebar pieces would be sticking up like dandelions similar to the way that they stuck out where the bottom of #11 was torn out by the post-tension bar. Instead it appears they were sheared clean off, even with the top of the deck.

The anchor at the bottom of #11 retained enough grip to tear through a significant amount of reinforcement in #11; that suggests that there was no damage to the anchorage. I believe any load through the lower post-tension bar was relatively slowly relieved due to the inertia of the concrete mass.

A significant amount of damage was done to the upper end of #11 as the axial load that it was supplying was lost and it was converted to a cantilever, along with the canopy, temporarily sharing the load until they too succumbed as the rest of the bridge rotated from the south platform due to unbalanced gravitational loads. The load transfer to the canopy was delayed because the reaction was through #12, but #12 was displaced from the deck by the movement of #11.

I think the critical movement was less than a few inches, perhaps as little a one inch of shear, at the bottom of #11.

 

[jrs87]

Denney Pate - Linda Figg - MCM designs for another project:

http://www.fdotmiamidade.com/userfiles/files/Signature Bridge Renderings_Fluor-Astaldi-MCM.pdf

Bonus Pate articles:

http://ravenelbridge.net/cable_stay_cradle.pdf

http://www.structuremag.org/wp-content/uploads/2014/08/D-Spotlight-GlassSkyway-Oct091.pdf

https://roadsandbridges.s3.amazonaws.com/s3fs-public/38_JordanBridge_1112RandB.pdf

Linda Figg:

http://www.dot.state.mn.us/stcroixcrossing/pdf/figg.pdf

Jose Mejia "[bridge] had some opposition" 2:14

https://www.nbcnews.com/ali-velshi/...ollapse-recounts-the-experience-1186883139724

Who is Jose Mejia? (Even innocent bystanders are questionable there.)

http://www.miamiherald.com/news/local/community/miami-dade/west-miami-dade/article160749219.html

http://forums.leoaffairs.com/showth...inal-Mejia&s=c8a43026ad52a94606d9824837b8d880

 

[SwinnyGG]

MCM stated the bridge design was efficient. What does that mean?

In my mind 'efficient' with regard to a structure means that the structure does its job with a minimal amount of excess material.

Efficiency can be attained by either using design elements that handle specific situations very well (for example- steel cables for tension-only members instead of heavier sections).

It can also be attained by getting the real-world structure as close to the actual required safety factor as possible such that the structure is as light/slender as it can be while still doing the job.

 

[Alpha Kai]

Deck hinged 11/12 and fulcrum upward and backwards before deck was pulled out from underneath it.

https://www.youtube.com/watch?v=9X8FIFPnDh0

This video will resolve your questions on why the PVC pipe presents with ''no damage'' and the reinforcement being in such great condition. Also, explains why some of the bottom of 12 and 11 are ''destroyed''.

Further, the "Polish guy's video" has the top of the canopy ''pivoting in mid air!" - that video should totally be discounted.

 

[CCW1]

OK, so we know that sooner or later some rich Caribbean Playboys returning home from a trip to Disney World, will decide to leave a memorable departing maneuver by flying their Lear Jet under the FIU Pedestrian Bridge Tamiami Trail Clear Span, about 2:00AM when traffic is light and only a few homeless camper tents and parties going on the overpass.

They misjudge. According to AASHTO will the "vehicle impact" exceed the design requirements for vehicle impact loads on the structure?

 

[SFCharlie]

This video will resolve your questions

I have followed "Philadelphia Construction Engineering" and "Construction Engineering and Photography" since his first video on the bridge collapse. Sometimes he thinks so quickly I can't keep up. He also digs up source material that I was not aware of. I believe he has proven that the collapse is caused by a number of different sources in different videos. I haven't watched the entire hour and 20 minute latest video (sometimes, I don't have the patience to listen to his redundant and disorganized narration). I did drop in on it's live broadcast and got totally confused. I'm working on a frame by frame reconstruction from the original dashcam footage, but I'm still in the learning curve, more later.

 

[chris snyder]

Interesting video above. I saw a bit about the fall begin ~30:00, about #12 breaking from deck ~31:35, and more about the fall ~40:00. I didn't watch entire video, so missed explanation of exploding concrete. I may watch all later - the author brings up some good points but it takes time to get them...

Been thinking about tension cables maintaining deck and canopy length while providing hinge points, and what happens to the diagonals (esp #11). Video shows a white area on #11's banner - can't tell if this moves much (would need to move north to sheer bottom end). The #10/11/canopy connection and canopy are weak, so it's possible this broke and top of #11 moved south (per epoxybot above) while the rebar held at #11/12/deck until it (maybe?) pried out. In any case, a LOT of weight would transfer to top of #10/11 during collapse, with bottom of #11 ~held at its elevation.

Thanks to MOJOJOHN's and others for input. The only things I'd say are ~definite now are #12 moved off the end of deck, #12/canopy joint stayed at a right angle, and the deck and canopy broke/hinged but stayed the same length.

To do an accurate cutout model (appreciated that video..), the whole span should be set up with a canopy hinge at the north end of #10/11/blister, a deck hinge at north end of #9/10/deck, with the south end of span hinged at the pier (this was on bearings and had moved north about a foot when #9/deck ~touches the ground). Would look at the collapse up to this point - the canopy break is ~touching #11 which is lying ~flat on the deck.

Below is photo of #9 - this had no PT rods, but punched through the canopy and remained ~intact, while #8 diagonal (with 4 PT rods) broke up. The blister at #8/9 shattered. This got hit with different forces, but seems to indicate the blister/canopy/truss areas were weak (may be able to measure photos to estimate how much of upper #11 is buried).

 

[chris snyder]

One other thing (bugged me since someone asked "What happened to the cage?") - is this a welded or wired assembly, and is this the rebar MOJOJOHN said would shear when #11 moved north? Is hard to imagine the cage lifting or shearing without affecting the lower rod anchor (seems cage moving out would break/loosen up the concrete, but lower anchor held tight to strip the lower rod).

 

[3DDave]

It takes a shear movement of less than half the thickness of material to separate it. Since the re-bar is smaller than the clearance of the post-tension bar inside its sheath it is easily possible to cut all the re-bar at the deck surface and leave the post-tension bar unaffected.

 

[bimr]

Denney Pate - Linda Figg - MCM designs for another project:

http://www.fdotmiamidade.com/userfiles/files/Signature Bridge Renderings_Fluor-Astaldi-MCM.pdf

That is an interesting document. Linda Figg is claiming she is an Architect on page 2 but is not listed as being a registered architect in Florida. That is a crime in Florida.

In Florida, an "“Architect” or “registered architect” means a natural person who is licensed under this part to engage in the practice of architecture."

This is a good example of why it is important to be licensed.

481.223 Prohibitions; penalties; injunctive relief.—
(1) A person may not knowingly:
(a) Practice architecture unless the person is an architect or a registered architect; however, a licensed architect who has been licensed by the board and who chooses to relinquish or not to renew his or her license may use the title “Architect, Retired” but may not otherwise render any architectural services.

(c) Use the name or title “architect” or “registered architect,” or “interior designer” or “registered interior designer,” or words to that effect, when the person is not then the holder of a valid license issued pursuant to this part.

(2) Any person who violates any provision of subsection (1) commits a misdemeanor of the first degree, punishable as provided in s. 775.082 or s. 775.083.

​

(d) $1,000, when the conviction is of a misdemeanor of the first degree.

​

f) Any higher amount equal to double the pecuniary gain derived from the offense by the offender or double the pecuniary loss suffered by the victim.

​

(g) Any higher amount specifically authorized by statute.


(3)(a) Notwithstanding chapter 455 or any other law to the contrary, an affected person may maintain an action for injunctive relief to restrain or prevent a person from violating paragraph (1)(a), paragraph (1)(b), or paragraph (1)(c). The prevailing party is entitled to actual costs and attorney’s fees.

(b) For purposes of this subsection, the term “affected person” means a person directly affected by the actions of a person suspected of violating paragraph (1)(a), paragraph (1)(b), or paragraph (1)(c) and includes, but is not limited to, the department, any person who received services from the alleged violator, or any private association composed primarily of members of the profession the alleged violator is practicing or offering to practice or holding himself or herself out as qualified to practice.

 

[CCW1]

to BIMR
Same here. And to be found practicing outside or beyond your professed and demonstrated level of expertise, (say, your stamp and signature was found on an elevator control drawing) even though carrying the PE license, brings on similar sanctions and penalties.

 

[Ingenuity]

That is a crime in Florida.

However, Florida (and many, many other states) permit union craftsman to call themselves "operating engineers": Link

(c) Use the name or title “architect” or “registered architect,” or “interior designer” or “registered interior designer,” or words to that effect, when the person is not then the holder of a valid license issued pursuant to this part.

Give me a break - the name and title of "interior designer" is protected too!

 

[hokie66]

I agree that engineers and architects need to be registered, but in the case of this bridge, I imagine that is the least of the Figg firm's worries.