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Miami Pedestrian Bridge, Part VII
48

Miami Pedestrian Bridge, Part VII

Miami Pedestrian Bridge, Part VII

(OP)

RE: Miami Pedestrian Bridge, Part VII

Quote (dbill74 (Mechanical)15 May 18 13:53 With all the talk of tensionnig of cables and fancy graphics of stresses in the members and what not, there is one aspect of this bridge I have yet to see anyone address.)

Please see:
LittleInch (Petroleum)26 Mar 18 14:18 in:
(Search (control F) for the date is easiest)
In thread 815-436924: Miami Pedestrian Bridge, Part IV

In fact I've read all six parts. I am amazed at how many of the long standing members nailed it back in Part 1.

RE: Miami Pedestrian Bridge, Part VII

Quote (SFCharlie)

I am amazed at how many of the long standing members nailed it back in Part 1.

Ya... two months ago, thereabouts... Some of the long standing members have decades of experience. not at all surprising.

Dik

RE: Miami Pedestrian Bridge, Part VII

I think now though with new testimony it is clear that the rods in no 11 were being tightened to "pull up" the column and close the crack(s) at its base.

I still don't have a clear view whether the top or bottom of no 11 failed first but my probable cause is the bottom.

The design does appear to be at best "non srandard" and at worse poorly analysed.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Miami Pedestrian Bridge, Part VII

Hopefully when the NTSB releases their preliminary report, they will also release the actual Traffic Cam footage. I don't accept that they failed to record and make a copy of the Traffic Cam footage. Indeed, if they in fact failed to record the incident, then that itself requires an investigation. Shortly after the accident, they shut down the public feed of the traffic cam and have since, removed the cam from the public website menu.

RE: Miami Pedestrian Bridge, Part VII

I looked some, but couldn't find how to calculate/estimate self-weight point loads.

Some have assumed a percentage of total weight on upper/lower nodes (33%, 67%), then divided total weight to get kips/foot.
I tried by calculating volume of components, dividing total volume into total weight, then distributing it to each node with canopy, blister weight on upper nodes, and deck, truss, diaphragm on lower nodes. End result (12017 cf/950 kips) yielded 158 lbs/cf - heavy for concrete (150 lbs/cf), but there's steel in the span.

I'd appreciate if someone could give me guidance (if simple) or a link to read.





RE: Miami Pedestrian Bridge, Part VII

I would normally treat the top chord as a continuous beam with supports at the panel points and use the reactions obtained as the point loads.

Dik

RE: Miami Pedestrian Bridge, Part VII

Quote (epoxybot)

Indeed, if they in fact failed to record the incident, then that itself requires an investigation. Shortly after the accident, they shut down the public feed of the traffic cam and have since, removed the cam from the public website menu.

One of my concerns about the report from the NTSB.

Dik

RE: Miami Pedestrian Bridge, Part VII

jrs87 - This is the best I can supply. When I first checked about a week after the bridge collapse, my recollection is that there were 3 traffic cams on US41 and now there are none. Perhaps they are all part of the same feed network. Maybe there is construction work that has disabled them but why the no longer appear on the traffic cam map is odd.

Link

RE: Miami Pedestrian Bridge, Part VII

Another possible sign poor judgement was used designing bridge. Several feet of free passage width were to be used for planters, benches, and tables? If so, to use this much width for non-function use is pure folly. We all know any increase in width for a suspended load comes at a non-linear cost. I hope to run numbers to see what a practical width would be for expected foot traffic. Decided not to bother when I discovered stairway on north end was to be less than 11 feet wide and the elevator is small. So they meant it when they said this bridge was to be "floating public space". This is a world-wide growing trend, parks and gardens on rooftops for example.

We may be a victim of our own success. Failure is so rare, people stop realizing danger is there. Building this bridge was dangerous... because building ALL bridges is dangerous.

RE: Miami Pedestrian Bridge, Part VII

Quote (epoxybot)

If the canopy isn't stressed before #2 & #11 are stressed, wouldn't the canopy crack somewhere between the 2/3 & or 10/11 blisters?

Difficult to say. Members are short so axial deflection would be small. That said, I'd be surprised if any of the diagonals were stressed prior to the longitudinal PT.

RE: Miami Pedestrian Bridge, Part VII

2


Quote (epoxybot (Structural) )

Hopefully when the NTSB releases their preliminary report, they will also release the actual Traffic Cam footage. I don't accept that they failed to record and make a copy of the Traffic Cam footage. Indeed, if they in fact failed to record the incident, then that itself requires an investigation. Shortly after the accident, they shut down the public feed of the traffic cam and have since, removed the cam from the public website menu.


That is a video camera detector for sensing vehicles in the left turn lane. Video camera detectors are a new sensor technology in use at some traffic signals. These detector systems use digital image processing to detect a change in the image at a specific location in the travel lane due to the presence of a vehicle. Video camera technology potentially allows a wider variety of vehicles to be detected than with inductive loop sensors, but the camera must be properly installed and adjusted for this to work.

Will not have a wide vision and most likely would have not picked up the bridge collapse.



A traffic detection camera

RE: Miami Pedestrian Bridge, Part VII

bimr: thanks for confirming that (and 3DDave for the link). In CA they have (old tech) sensors under the pavement to detect traffic/regulate signals. In MO they have these cameras at newer intersections - I'd wondered if they were for red light runners [at a new intersection by my house, after a year the lights were still badly timed.. been in CA 6 months so maybe they programmed them by now].
-----------------------------------------
Below is tensioning sequence for mainspan.

The 2/6/18 memo said hairline cracks only in #3 and #10 showed after stressing rods in #2 (on 1/30/18) and #11 (on 1/29/18).
The 2/28/18 memo said bad cracks at base of #11 showed after the formwork was removed - which is what triggered the cracks (cracks happened before repositioning SPMTs, cantilevering span ends, moving the span, etc - which removes most of the ABC concerns of building elsewhere/moving into position). This should have raised red flags since three of four engineers who only saw the photos said it indicated eminent failure. I'd like to know how far the #11/deck crack in Photo 4 extended toward the north end.

RE: Miami Pedestrian Bridge, Part VII

jrs87 - So many things about this project's stated objectives are nonsense. I watched an interview with an FIU student after the collapse, the student mentions during the conversation that HWY 41 traffic (5 to 6 lanes) is pretty noisy. Now imagine vehicles at a stop, under a bridge and the noise, that generates. The whole idea of a "Public Space" was silly. What above exhaust fumes?

Has anyone checked with major paint manufactures to find out if TiO2 in paint & formulated for concrete behaves in the same self-cleaning manner as these TiO2 parge coats? Parge coats are labor intensive and this bridge is a good example of how variable this kind of application coverage can be.

In the original planning proposal used for directing Design/Build bidders, T.Y. Linn's bridge recommendation was for a steel & concrete truss design because truss structures were recognized as good examples of how a structural element & missile screens could come together in function & architectural presentation. The bid request specifically called for the Missile Fence to be incorporated into the structure rather than free standing. FIGG/MCM seems to have completely ignored this concept and it makes me wonder what the proposals by the other two bidders looked like. The FIU selection committee bares some responsibility for discounting T.Y. Linn's recommendations and choosing a "Never Been Done Before" design, when the entire premise of the project was Safety. Maybe the Miami-Herald should ask to see the other bidder's proposals. Granted Facchina Construction Company the final remaining bidder is now defunct.

RE: Miami Pedestrian Bridge, Part VII

Epoxybot, yes the selection committee was up to something. MCM claims three different proposals and sleepless nights in the announcement of securing another win (Winning!)

http://www.mcm-us.com/news/mcm-awarded-fiu-pedestr...

Don't rule out existence of more dashcam video, even from crushed vehicles.

RE: Miami Pedestrian Bridge, Part VII

Clear (and blocked) view of blister. Is see nothing remarkable. According to Internet, this photo was taken on day of collapse and this worker was on canopy at time of collapse and survived. I have his full name, but choose not to disclose it at this time. My question is, can anyone here determine markings on hardhat? I'm curious who he worked for. It seems to me three people only does not add up if they were trying to mitigate cracking. Who was monitoring cracking as they changed stress?

RE: Miami Pedestrian Bridge, Part VII

I wonder if this is the worker who latched his harness when he heard a crack - I thought he may have been hidden behind the crane with harness suspended from it. Three Structural Technologies workers were there - Mr. Brown, and two went to the hospital, but I never read any more about the third. A couple comments somewhere said no one was watching the cracks, but it'd be logical to do so if rods were tightened to close them (maybe even Denney Pate) - if the road wasn't closed, no one should have thought it hazardous to stand there.
https://wcinsights.com/worker-dies-in-fiu-bridge-c...

This came out a couple days ago about the crane and explains why post-collapse photos only show the bucket lift.
https://nypost.com/2018/05/14/crane-operator-fled-...

RE: Miami Pedestrian Bridge, Part VII

Quote (chris snyder)

"latched his harness when he heard a crack"

Yes, worker in photo is the one reported to latch harness. According to his cousin, he credited it with saving his life.

About the crane operator, he jumped out the crane very quickly and seemed to understandably panic. Media reports he fled scene seem unfair.

Opinion on accident by actual forensic engineer: http://www.hgcornerstone.com/blog/expert-witness-b...

RE: Miami Pedestrian Bridge, Part VII

(OP)
jrs87, there’s way too many unnecessary sentences in that article , but a few comments:

”While the exact cause of this astonishing bridge collapse and horrific tragedy is not yet known” ….
yet:
“Secondly, no new, previously unknown, engineering principle or precept will be learned or discovered here concerning the exact cause or failure mechanism.
We will only learn how known, well-understood, engineering principles or precepts were somehow violated leading to this sudden bridge collapse.”

So the cause is not known yet – but he knows that we won’t learn anything new from it.

“The structural design concept of the bridge decks mainly involved a concrete truss reinforced by post-tensioned steel tendons. A 109-foot high central pylon, yet to be constructed, would have added more steel cables, and thus more stability, to the overall structure.”
The cables were aesthetic – as this series of threads has revealed – so this forensic engineer is discussing something he isn’t very familiar with.

“However, it is entirely fair to begin asking some very crucial questions about what, as engineers and builders, we should be focusing on during the investigation and what things we may need to modify or change as a result of this tragedy to prevent something like this from ever happening again.”
Tragedies won’t be “prevented” by “modifying things” – we only can attempt to minimize the future risk.

“But, the most important and crucial take-away is that this tragedy should never have been allowed to happen in the first place and cannot be allowed to occur again in the future.”
Let’s make a law against this sort of tragedy shall we?


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RE: Miami Pedestrian Bridge, Part VII

chris snyder, Thanks for the post-tensioning sequence. I knew it had to be spelled out somewhere, but I was just too lazy to find it.

Before you posted it I was just assuming that the deck was poured, then all deck tendons were stressed, prior to working up and casting the diagonals. But now I see this is not the case. And it raises an interesting question: Why? Since everything was supported on falsework I don't see the need to wait until entire superstructure is cast before beginning stressing operations on the deck. Does anyone have any ideas as to why you'd want to wait?

The reason I raise this question is the following:


By waiting to stress deck PT, aren't you unnecessarily introducing into the system a shear force at the base region of member 11? This would be locked in, and subsequently added to the shear loads generated from dead loading when the falsework is removed. Wouldn't it, or am I missing something?

We'd expect to see the same "shear lag" effects that have been thoroughly discussed elsewhere in this thread with respect to the dead load. And the deck is much stiffer than member 11. So most PT force will stay in the deck, but some fraction will move into member 11. It's hard to say if this is a significant load. A computer model would tell the tale of the stress history.

RE: Miami Pedestrian Bridge, Part VII

thebard3: The page you linked on MCM's website calls this a cable-stayed bridge. OOPS. Like you, I am also surprised this page is still up.

JAE: "Let’s make a law against this sort of tragedy shall we?" That's my kind of rhetorical question. Unfortunately, legislators (who are mostly lawyers) think this is actually possible. BTW, the Kellogg-Briand Pact attempted to legislate war out of existence. Except for WW2 and a few other minor skirmishes, it seems to have worked quite well. Not. Both ideas--legislating away tragedy and war--are hopelessly naive. i suspect you knew that already. smile

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Miami Pedestrian Bridge, Part VII

jrs87 - Well the hard hat doesn't look like MCM or FIGG's logo. Structural Technologies is part of Structural Group and includes a number of different companies. Their Pompano Beach office includes VSL, Structural Technologies & Structural Preservation Systems, perhaps more. Structural Group is the product licensee of VSL/Bouygues. Structural Technologies prominent use of the VSL on much of their marketing & company property tends to give people the impression they are VSL. VSL/Bouygues does contract worldwide but mostly they license their products in various regions of the world. I don't think Structural Technologies can necessarily contract as a licensed VSL installer. Their is at least one email that mentions that the company performing the Post Tensioning is not VSL.

There is this tweet from Monique O. Madan at the Miami-Herald about an hour after the collapse. It makes me wonder if the construction workers had growing reservations about the bridge as it was getting built. It looks like they spent at least half a day of crane time trying to set the rebar cage for #12.
Link

I shudder at my past experience working with Universities & Healthcare, they turn on a dime making decisions about projects already in the works without a thought to the price already given for the work contracted; while acting like they are a poor as church mice. They really do expect you to shove 10 lbs of fudge in a 5 lb bag, with your head up in the clouds, where they can talk to you.

RE: Miami Pedestrian Bridge, Part VII

JAE: I had a couple of exceptions to his comments, but, for preliminary comments they were a reasonable summary. In addition to your items, my two exceptions were; I would normally think that a forensic guy might be a little more constrained:

...whatever did go wrong here either could have been prevented, or at least could have been better accounted for such that loss of life and catastrophic damage did not ensue.

Although this appears to be a structural issue, with the bridge barely capable of supporting the actual dead load. It is possible that some of the fatalities could have been avoided. What if there had been a crew of 30 construction workers on the deck or canopy?

Secondly, no new, previously unknown, engineering principle or precept will be learned or discovered here concerning the exact cause or failure mechanism. We will only learn how known, well-understood, engineering principles or precepts were somehow violated leading to this sudden bridge collapse.

I would not be making that statement until all the 'dots were on the dice'.

RE: Miami Pedestrian Bridge, Part VII

As to the MCM page linked above still being online, I imagine there is some discord between parties now. The contractor probably prefers to emphasize the role of the engineer, and the photo with the beaming dials of Linda Figg and Denney Pate front and center serves that purpose. Or am I just being cynical?

RE: Miami Pedestrian Bridge, Part VII

How much did the length of the bridge deck change during post-tensioning? I just read several articles about PT, but didn't find anything about how much the concrete would be compressed in a typical case. I'd guess several thousandths of an inch per foot, but I'd like to know for sure.

RE: Miami Pedestrian Bridge, Part VII

If I am reading it** right, modulus of elasticity is about 5 psi/ppm. In #11, the area is nominally 500 inch^2 and the post-tension was 560 kips, so the average pressure is about 1120 psi, so the length change 224ppm. An approximation of the beam is that it is 33 feet long - so about .0074 feet; 0.09 inches. In contrast the total delta on the tension members is 1.40 inches.

I'm not doing this for the deck because I'm lazy and don't care to find the section area, the preload, and the tension that offsets the pre-load when it's installed.

**https://www.engineeringcivil.com/modulus-of-elasti...

(Feel free to check the math, but the ratio seems about right.)

RE: Miami Pedestrian Bridge, Part VII

Greetings to all

Regarding the stressing operations:

All stresssing. deck, canopy and diagonals, were made in 1 phase after the main span was cast on temporary supports at the side of the road.

Mr. Toomas Kaljas, whose analysis was posted in a previous thread, has revised his analysis incorporating the PT based on the existing published contract plans. The analysis show that almost all the load goes to the deck or the canopy because their stiffnesses. The diagonals get only a small load. For practical purposes, worthy of not being accounted for compared with dead load.

Good hunting...

RE: Miami Pedestrian Bridge, Part VII

Hokie... opens up an interesting legal issue. Was the collapse in the realm of the Contractor or the Engineering Firm.

Dik

RE: Miami Pedestrian Bridge, Part VII

Dik-- I'm sure everyone will share in the liability fest sure to follow this, including the University.

RE: Miami Pedestrian Bridge, Part VII

There seems to be a unique osmosis regarding liability in most litigation, it tends to flow toward the deeper pockets.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Miami Pedestrian Bridge, Part VII

ON: That's why I'm curious about the FDOT's involvement... deeper pockets.

Regarding Contractor and Engineer... I was thinking more about criminal proceedings...

Dik

RE: Miami Pedestrian Bridge, Part VII

The worker in photo I posted May 16 is employed by Bolton Perez and Associates. https://www.bpamiami.com/2012-bpa-employee-awards/


Quote (The Mad Spaniard)

"... deck or the canopy because their stiffnesses."

Mad, this has me wondering if the bridge was just a deck and nothing more, would it have been able to stand on its own unloaded? Maybe. Not trying to make an important point here, just a thought exercise. The whole idea of a truss is to replace columns under the deck with members in tension on top. The weight of the canopy and members would not be applied to deck.

RE: Miami Pedestrian Bridge, Part VII

Greetings jr87

Given their thickness, the canopy and the deck can not span the 175 feet by themselves. The system acts mostly as a truss for dead load and live load. Now, it can also be considered as a "beam" the same way that you take a concrete beam and the shear is evaluated using "truss" behaviour having a compression flange at the top and a tension flange at the bottom.

Now, at the ends of the span, we may have a little of "beam" behaviour because the north temporary supports are distributed transversally and we do not have a support directly under member 12. For the south, we have two bearings 5 feet away from the centerline. These two details may have some effects on the "truss" behaviour of the bridge. As I have not done a 3-D analysis, I can not say where we are.

For the longitudinal PT in the canopy and the deck, the results from Mr. Kaljas indicate that the diagonals get very little load and that most of the straight tendon compression force is absorbed directly by the canopy and deck.

Typically, the canopy should not have longitudinal PT because it is in compression. However, because the back span is attached to the main span at the end of construction. the structure acts as a "two span continuous beam" and therefore there are tension forces at the canopy near the pylon due to live load. Also, because the back span is let go after being attached to the main span, this causes negative bending near the pylon with the corresponding tension forces in the canopy. This is probably, why the designer placed PT in the canopy. Also, for symplicity, they may have decided to extend the tendons all the way to the ends. At the ends, I doubt that you need so many tendons...

Best regards

Live long and prosper.

RE: Miami Pedestrian Bridge, Part VII

Mad, thank you. I was thinking how much thicker would deck have to be with no truss or canopy at all. Would a more pronounced v-shape have helped? What kind of moments did this bridge have?

I'm beginning to suspect they really did break something while adjusting bar tension, and like a tiny pin point bursting a balloon, 11 popped. It seems to me for span to fall under dead load only, the defect must have been severe. Too bad water bottle load test was not done. https://www.youtube.com/watch?v=12s42VorvQ4

Why was T.Y. Lin's much sounder concept rejected? It seems ABC was non-negotiable. ABC as advantages, but it does not obsolete older methods. When you're holding a hammer, everything looks like a nail. https://www.youtube.com/watch?v=EfH46DTAkxo

RE: Miami Pedestrian Bridge, Part VII

jrs87: He seemed to have missed the EoR in his list; for financial reasons he may not be a target. In some jurisdictions, you can sue the engineer, the company, and, the engineer and company jointly. This adds to the permutations. Then there are party's within the group that will cross-sue other parties... it' going to be a real 'fuster cluck'.

The Spaniard: There are a few ways of looking at the framing for the bridge, but, at the end of the day, there will be a similar stress condition throughout the bridge. Treat it as a truss, treat it as a beam. A realistic model of the framing will yield similar results.


Dik

RE: Miami Pedestrian Bridge, Part VII

The prosperlaw fellow is a personal injury lawyer, otherwise known as an ambulance chaser. The other side of this is the construction defects civil lawsuit, in which I think FIU would be the plaintiff. And then there is the possibility, as dik indicated, of a criminal action.

RE: Miami Pedestrian Bridge, Part VII

In this locale, lawyers use a 'scattergun' approach... lawyers can be sued if their case fails and there is someone that was missed. Someone they should have sued, and, didn't.

I suspect FDOT will figure heavily into this. I assume they are like most government agencies who disclaim involvement... but are at the table for all morsels and scraps. Governments seem to thrive on involvement. I noticed the lawyer included them in his list of ???

They may have positioned themselves into first place.

Dik

RE: Miami Pedestrian Bridge, Part VII

Greetings jrs87 and SFCharlie

Regarding the Bridge Testing, in Spain , for instance, it is typical to perform a load test on a bridge after construction to everify its behaviour in service. See below some examples.









As you can see, it is done with trucks full of sand. Several arrangements are perform to evaluate the critical load conditions.

In the USA, well... I have not heard of any load test similar to thos that can be sen in the pics.

for the moments in the Miami structure, Mr. Kaljas has shown somenumbers.

Best regards

RE: Miami Pedestrian Bridge, Part VII

Quote (3DDave)

If I am reading it** right, modulus of elasticity is about 5 psi/ppm. In #11,.. 33 feet long - so about .0074 feet; 0.09 inches. In contrast the total delta on the tension members is 1.40 inches.

This relates to what GreenLama brought up about the deck not being tensioned before the members were poured. I (no structural background) never thought about concrete compressing. If relative to 0.09" over 33', the 174' deck would compress about 0.5" which would stress the rigid member connections (along with tensioning in the canopy), to pull in the bottom and open the ~36o angle of #11. It isn't much, but could this add to the problem of a weak 11/12/deck connection?

RE: Miami Pedestrian Bridge, Part VII

(OP)
Mad Spaniard....they must pay those truck drivers a LOT of money to load the bridge and stand their waiting to see if it collapses or not.

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RE: Miami Pedestrian Bridge, Part VII

Quote (MacGyver)

I'm reminded of a Prince Rupert's Drop

Used to make these as a kid... the neighbourhood guys just loved them. So tough and yet so fragile.

Dik

RE: Miami Pedestrian Bridge, Part VII

Quote (chris snyder)

...compress about 0.5"

Modulus of elasticity: AASHTO Load and Resistance Factor Design Manual Sec 5.4.2.4

Tendon stress can easily compress 175 foot span a visible amount. I don't know what PSI they pulled tendons at (6500?), and I don't know what happens as concrete continues to cure after post tensioning. It's correct to be concerned about the effect of this on truss system. It's not related to this accident, but concrete can also creep and stretch.

RE: Miami Pedestrian Bridge, Part VII

Harry Pepper in Florida can do load test:

RE: Miami Pedestrian Bridge, Part VII

greetings again jrs87

I am 100% sure that the designer made an analysis accounting for the time dependent properties of concrete (creep, shinkage, increased strength with time) and post-tensioning (relaxation) with a computer program that accounted for the changes in structural scheme during the relevant construction phases. This is typical of such structures in the State of Florida and there are many commertialy available programs that so so (SAP2000, LUSAS, LARSA, etc...)

We can expect that the analysis would have results at the times of casting the main span, post-tensioning the main span, moving the main span, placing the main span in the supports, casting the back span, stressing the back span tendons, stressing the continuity capony tendons, releasing the falsework, casting the pylon and attaching the stays, end of construction and 10,000 days after the end of construction (and potentially several other intermetiate time and construction phases).

The computer program would have accounted for the fact that the PT was stressed when the strength was 6500 psi and would have given very slightly different results (but not of the magnitude that would cause failure) if it was instructed to streess when the strength would have been 8500 psi.

So, let's see what the designer's calculations tell us or what some brave soul out there like Mr. Kaljas has gotten for all of us.

And BTW, I am sure that they moved the span when they were sure that the concrete strength was 8500 psi. Even if the Contract drawings do not say so in the erection sheets.

RE: Miami Pedestrian Bridge, Part VII

The Mad Spaniard,

One drawing is missing within the updated work done by Mr Kaljas. There is no drawing showing the loads in ALL members resulting from stressing of the longitudinal PT. Take member 10 for example. If I'm reading his presentation correctly:
Axial-PT = 1570 K
Axial-DL = -862 K
Axial-total = 830 K

However, 1570-862 = 708 K, which is a difference of 122 K. I don't expect Mr Kaljas to redesign this bridge for us, but I was just curious. Thanks.

Dead Loads:


PT Diagonals:


Longitudinal PT:


Dead Load + Total PT:

Link

RE: Miami Pedestrian Bridge, Part VII

Mad Spaniard, despite our picking apart this project, I fully agree designer accounted for all the core details we bring up. Conversely, I do feel the standard to criticize the concept (not the engineering) of this bridge is looser. And no computer program as an output that says you can skip empirical testing of a new concept. I believe the biggest contribution of this thread is providing strong evidence this design concept and building technique combined is untested and unproven worldwide. Kansas City and Columbia both occured while I was in college and made a lasting impression on me.

The rubble fracture is consistent with 8,500 PSI. Aggregate snaped. I have seen some analysis that states over reinforcement with re-bar can be just as bad as too little as it removes what little ductility there is. I don't know.

P.S. Sorry about the load test image.. did not mean to go there. I've tried to quit this thread many times, but it's too intriguing. My son is in high school and the events in Texas this morning have left me stunned, so I think I will quit now for a while.

RE: Miami Pedestrian Bridge, Part VII

Greetings TheGreenLama

The axial PT value (1570 Kips Compression) that you mention is the result of applying diagonal PT bars to the truss. . It does not include the effects of the longitudinal tendons in the canopy or the deck. The dead load effect (862 kips tension) Plus the effect of the PT bars (1570 kips) plus the effect of the longitudinal tendons in the canopy and the deck ( 122 kips compression) provides the total of 830 kips compression.

So what happens is that even if you prestress the heck out off the deck or the canopy , the relative stiffness between the longitudinal members (deck and canopy) and the diagonals causes the diagonals to get very small axial forces out of it.

Best regards

RE: Miami Pedestrian Bridge, Part VII

Greetings jrs87

What has been happening lately in our high schools is very sad. I never had to worry about it very much here in the South when my daughter was there 12 years ago. I understand your distress.

But keep in touch with this thread. At the end, when we learn the reasons for this failure , I am sure that our faith in math and physics (and code requirements) will be rewarded.

Be well.

Live long and prosper.

RE: Miami Pedestrian Bridge, Part VII

The Mad Spaniard,

I don't want to belabor the point about what is likely a rough computer model, but what you're saying about the change in axial load (122 k) from the application of the longitudinal PT amounts to a 15% change in loading in member 10. I don't consider that insignificant. Are there moments generated as well within the system from the PT loads? For me that would be a disastrous by-product, due to the minimal shear reinforcement provided in the diagonals.

Thanks

RE: Miami Pedestrian Bridge, Part VII

A lot about analysis is being discussed here, but not much about design, which is a different part of our discipline. This was a new and flawed conceptual design, and should have been subject to rigorous experimentation and/or load testing.

RE: Miami Pedestrian Bridge, Part VII

hokie66,

As this thread is getting so long, have you ever thought about breaking it up? Say:
1) Analysis of existing as-built structure.
2) Failure mechanisms.
3) Failed design standards.
4) ?

RE: Miami Pedestrian Bridge, Part VII

TheGreenLama: too much work, and when the NTSB report comes out, there will be another flurry of information.

Dik

RE: Miami Pedestrian Bridge, Part VII

No, I see no need to break it up. I think it will proceed in spurts, as more information becomes available, or probably as more brainstorms occur.

RE: Miami Pedestrian Bridge, Part VII

Is this duct from "upper" bar? I would not expect to see it poking out here so far away from other edge without more local damage to beam. Duct for lower bar is shown in other images still around bar going to deck.

See attachment for high resolution.

RE: Miami Pedestrian Bridge, Part VII

JRS87....
That would be a west side view. That is the bottom side #11 tendon conduit, which I believe would be a short conduit section. I believe the tendon broke somewhere near there. When the canopy hit #11 at the top 2/3, it the snapped tendon, & ejected past Mr Brown. The conduit section below this area, terminates in the rubble, & as such, appears intact.

RE: Miami Pedestrian Bridge, Part VII

I agree it's a duct from #11's lower tendon, but suspect it's a section that remained as the rod stripped from the member - not sure what held the duct - it looks like it may be split. As some others here, I suspect the rod got pushed out as the deck fell instead of breaking. I redid the rough 'before/after' diagram using ~arc of the rod (in the bottom photo) - this makes the two rods about the same length, including the portion extending from blister.

Taking a closer look, the duct (from deck) in rubble is splayed on the north side - thinking this happened when the members sheared and the rod bent while the anchor held. The duct that's against this end (in rubble photo) has a rib which appears to be missing from the duct that's still in the member. There are two holes in the duct near the rubble... these could be caused by thread friction as ~6 ft of rod are pushed out.


RE: Miami Pedestrian Bridge, Part VII

Cutterhead, Chris S., thanks. Okay, has to be lower duct. I will check how duct is manufactured to see if it is seamed.

RE: Miami Pedestrian Bridge, Part VII

Another view. A cracked edge of duct is worn through, so there is evidence duct was indeed pushed along bar towards deck. The duct still in the beam must have come from where the separation is around bar. And like Cutterhead said, the other section of duct moved in. Still, this looks odd and I see so obvious sign duct still in beam is split lengthwise. Nor do I have any idea what could have restrained it so neatly. Is there any chance this duct was for something else or is stray?

RE: Miami Pedestrian Bridge, Part VII

Greetings to all

I would appreciate your assistance.

I would like to see if the failure occurred at the interface between nodes 11-12 and the deck. For that, I would like to know if member #12 sheared at that interface. For that to happen (ball park) the length of the member after collapse should be about 15 feet from the bottom of the canopy to the top of the deck. At the back of the member the length should be 17.25 ft to account for the danopy end diaphragm.

At the back of menber 12, the distance from the top of the canopy end diaphragm to the bottom of the deck diaphragm is about (18+ 1.25 + 2 = 21.25 ft).

So if anybody can meassure the length of what remains of #12 using the pictures available, we can know where if failed at the bottom (ball park): at the deck interface (15 feet at the front, 17.25 ft at the back) or below the deck (17 feet at the front and 19.25 at the back) or at the bottom of the deck diaphragm (19 feet at the front and 21.25 ft at the back).

This info may have been noted before by one of you guys. It is just that I have not seen it.


Thanks in advance

RE: Miami Pedestrian Bridge, Part VII

The photos I've seen indicate that #12 is the same length after the collapse as it was before.

The bottom end is torn up from separating, but otherwise it's there

https://www.eng-tips.com/viewthread.cfm?qid=437029, comment timestamp 27 Mar 18 00:32

RE: Miami Pedestrian Bridge, Part VII

After considering gwideman's animated loop
https://www.eng-tips.com/viewthread.cfm?qid=437029, timestamp 28 Mar 18 07:00
and the stuck duct section, I drew out what might have happened.
There would be two causes for stripping the lower PT rod - when #11/#12 members sheer from/move off the deck, and when the deck drops.
Notes are on the drawing. I couldn't add rotation.
Bugged me that the triangle moving north in loop was dark, but it's likely in a shadow (see shadow direction of cars) - last frame shows lightening (moving out of shadow, pixelating, ???).
I estimated bottom of #11/12 would move north about 6' before moving back south - only about 2' is visible (hidden by ~2' of boom on bucket lift - right edge of boom ~lines up with north side of #12).

RE: Miami Pedestrian Bridge, Part VII

Chris Snyder,

Thank you for your postulation. Yes, this section of duct was indeed cut open by sliding bar threads, I see it now. Hope for this analysis to continue. Rotating images so member 11 is in it's precollapse position is a good idea.

RE: Miami Pedestrian Bridge, Part VII

chris snyder,

I'm not advocating one PRIMARY potential failure mechanism over another, but one thing to keep in mind, both in your photo montage as well as gwideman's photo loop, and that is that the total length of member 11 can NOT increase. As I see it, the only way for the base of member 12 to become visible is for member 11 to push it there. But the only way for member 11 to push it there, and maintain the same length, is for the base of member 11 to have, at least loosely, separated from member 12 and begin sliding up member 12. I think it's just geometry.

RE: Miami Pedestrian Bridge, Part VII

The Mad Spaniard - The back side of #12 is full length from canopy to deck. I tried last week to measure this and was not satisfied with the figures I was getting. As you can see on photos, there is only one cold joint on the back of #12. Upon collapse, #12 separates from the diaphragm just above the two rebar extending from #12 at the deck reinforcing plane.



RE: Miami Pedestrian Bridge, Part VII

For anyone interested, something from the vault: VSL Report, "Detailing for Post-Tensioning." [Link]

Too bad they don't discuss our 11-12 joint area. There's a lot of discussion about the tensile forces that develop behind, and between, anchorages using strut and tie diagrams. All this talk of possibly stressing PT in member 11 to close cracks made me think about whether adequate confinement reinforcement was detailed in the already critical zone where 11 intersects deck.

Just one more thing to consider.

RE: Miami Pedestrian Bridge, Part VII

Good reference.

Dik

RE: Miami Pedestrian Bridge, Part VII

For the non-structural engineers in this thread who are trying to follow along...

Can one of the structural gurus kindly define the term "confinement reinforcement"

I'm only about 70% sure that my understanding of that term is accurate.

RE: Miami Pedestrian Bridge, Part VII

2
The picture on page 2 and the diagram on page 8 of the reference TGL posted above might help.



RE: Miami Pedestrian Bridge, Part VII

For PT strand anchorages, the manufacturer provides spiral reinforcement directly behind the anchorage. It is still the responsibility of the engineer to check the zone situated further behind the spiral. For threaded bar systems no such spiral is provided by the manufacturer, so it is solely up to the engineer to detail this region.

RE: Miami Pedestrian Bridge, Part VII

Excellent explanation, thank you both.

RE: Miami Pedestrian Bridge, Part VII

Those picture represent confinement for the axially applied post-tensioning only. Similar to column ties, which confine the longitudinal bars when they are in compression.

In the Florida bridge truss/frame, there was also a lot of flexure and shear in the joints, and I think that was not accounted for.

RE: Miami Pedestrian Bridge, Part VII

That was my next question- so the confinement reinforcement for certain types of PT tendons is defined by the manufacturer of those tendons.

In cases where the confinement reinforcement is (for lack of a better term) 'included' with the PT strand design, how common is it that additional confinement reinforcement is required?

Or, asked another way, how easy is the oversight which appears to have taken place- no additional confinement reinforcement in the 11/12 nodes?

RE: Miami Pedestrian Bridge, Part VII

The type of connection at the 11/12 and deck slab node is unique to this world, so overlooking of development, anchorage, and confinement should not have occurred, whether there was post-tensioning involved or not.

RE: Miami Pedestrian Bridge, Part VII

I wouldn't go so far as to say no confinement reinforcement is provided. As far as I can tell, drawing B-61 [ Link] shows reinforcement details at the truss joints. To me it looks identical for all joints (except for truss member 3-4 where there actually is more). This is just a feeling, but I wouldn't expect this to be the case because loads are likely different at every joint: PT, axial, shear, bending. If anyone has been able to find in the design drawings a detail for additional steel called out for PT anchorages at these joints please post.

RE: Miami Pedestrian Bridge, Part VII

Understood. I apologize if my questions are causing us to go back over material that's been covered before- but for someone not at all versed in the minutiae of concrete design, this thread is like drinking from a firehose. It's terribly interesting but there's an overwhelming amount of information.

Re: reinforcement schedules shown in the post above:

The reinforcement shown looks to me (a non-concrete reinforcement engineer) to be remarkably light, compared to the references.

Much of it appears to be located in the 'general zone' and beyond (as described in TheGreenLama's reference graphic 2.2), especially at the critical 11/12 node.

Is localized crushing under the PT tendon fittings, where there appears to be almost no confinement reinforcement in the local zone, the potential initial failure mode the structural guys are seeing?

In the case of the upper tendon at #12, only the L-hooked bars appear to pass through the 'local zone' at that tendon's fitting, and based on the references I don't see how those bars provide much confinement since they develop tension (and appear to provide confinement) in only one axis.

When reinforcement schemes are analyzed, are bars loaded in bending considered to provide reinforcement, are are they disregarded?

RE: Miami Pedestrian Bridge, Part VII

Hay, I'm a computer scientist, so what do I know, but from what I saw in the drawings, the joint at 1 - 2 had 50% more rebar than 11 - 12. I wish I knew why they beefed up 1 - 2, and why they didn't beef up 11 - 12 at the same time? It's the human factor that throws me.

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

jgKRI,

I'll take a crack at some of your questions.

1) Reinforcement does look remarkably light and uniform.

2) Crushing should never be an issue as plate size will have been designed by manufacturer to transfer specified design load.

3) Circular anchorages for PT strand transfer load to concrete over a different surface area than the flat plate, thus the need for spiral steel immediately around that type of anchor. In other words, flat plates generally don't require spiral steel immediately behind plates.

4) Overall geometry of concrete section plays a role in how load moves from anchorage into structure. In our case it's not simple.

5) Generally, you'd only consider steel perpendicular to strand/bars to contribute. If it crosses at an angle you might consider a fraction of it to be effective, but there's no hard rule on this.

6) In the 11/12 joint area we also have a very large compressive force from dead load. I haven't quite figured how this impacts PT anchorages. I would think a good practice would be to still address anchorage zone issues regardless of other loads.

RE: Miami Pedestrian Bridge, Part VII

Quote (SFCharlie)

...why they didn't beef up 11 - 12 at the same time?

Member 11 was not inline with faux stay, so making it larger would disturb visual design. In another asymmetrical aspect of the design, the deck diaphragm on north end was much smaller than the one on south end.

Concrete bridge construction reference with excellent illustrations and warnings: https://www.fhwa.dot.gov/bridge/construction/pubs/...

RE: Miami Pedestrian Bridge, Part VII

Quote (jrs87)

In another asymmetrical aspect of the design, the deck diaphragm on north end was much smaller than the one on south end.

The south end of the span was designed to float independently on bearings with an expansion joint.
The north end would be fixed to the pier and supported (to a degree) by the backspan after completion.

The south end was a lot stronger, but still only had a rebar cage (no chevron ties, steel reinforcement, etc), thicker truss, larger base for #1/2, thicker diaphragm, #1 wasn't hanging off the deck (like #12), and the 3D stress was much lower (per Mr. Kaljas's analysis). I don't know if #1 had two ~3" vertical PVC pipes on each side and other "protrusions" from the deck (visible in photos). It was strong enough to hold during the collapse.

There was a problem at #11/12/deck because it cracked after initial PT tension and shoring was removed. They moved the span anyway, and first mentioned cracking after the move (those 2/28 photos are rather damning..). No one would have wanted to say or hear the span needed to be redesigned "just" because of that #11/12 node (as said one engineer in the Miami Herald article after he saw the photos). I'm curious if someone sensed it was weak, but that the north end would hold until bridge construction was completed.

RE: Miami Pedestrian Bridge, Part VII

2
Let me just add one more thing before I'm off for vacation. Looking at the geometry of drawing B-61 more closely (detail shown here), what's to prevent a good portion of the PT force of the bottom PT bar from going into the deck slab instead of diagonal 11? (Excuse me if this has already been talked about before by someone else; maybe chris snyder.) My strut-and-tie diagram is not very good, but I think the result would be to induce a tensile force at the inside corner, potentially resulting in splitting in this area. Reinforcement would need to be detailed to prevent this. Now we don't know if they were in fact stressing or destressing this bar at the time of collapse, but as a general rule the anchor location, geometry, and existing detailing is concerning.

RE: Miami Pedestrian Bridge, Part VII

Quote (chris snyder (Electrical))

I don't know if #1 had two ~3" vertical PVC pipes on each side and other "protrusions" from the deck (visible in photos). It was strong enough to hold during the collapse.
Thanks for your insights. #1 has four vertical PT rods, seen at the top and bottom hinges. The hinges also had the side effect of providing access to the PT rod couplings.

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

And then there's that pesky construction joint just above the anchors. We don't know exactly what it looked like because the forms for the truss were in place when the deck was poured, and we don't know how much time elapsed between the pours.

RE: Miami Pedestrian Bridge, Part VII

Quote (chris snyder)

it was weak

Thanks Chris, your post is right on. They had to know north end was... let's say non-optimal while bridge was incomplete as they designed it that way. I'm not saying they had malaise or were negligent, it's more subtle than that. I'm not sure movers knew about any problems because I have seen video of them casually hanging out under span. Comments from residents of area are appearing that pre-collapse called bridge an accident waiting to happen and noted how ugly it was. I digress, the ugliness of bridge is off topic.

The pdf I linked to discusses temporary use of PT bars during assembly.

Keep going Chris, I think all of us are happy with the quality of your posts.

RE: Miami Pedestrian Bridge, Part VII

Quote (TheGreenLama)

Crushing should never be an issue as plate size will have been designed by manufacturer to transfer specified design load.

With the concentrated compression loading, due to the differences in stiffness, with post-tensioning you often develop high tensile stresses. This is one of the reasons for the added reinforcing around the anchorages. It's often not for crushing.

Dik

RE: Miami Pedestrian Bridge, Part VII

I had hoped that the NTSB would release at least photos of the several bridge structural components that they are examining, that would show for example:
the end of the deck diaphragm that had been up against the pier
the end of the 10-11 blister that had been up against the canopy

I also hope that the start date of the embargo could be moved closer to the time of the collapse.

Maybe you who have questions that should and could have been addressed; would post them please.
Thank you all very much,

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII



I am puzzled that they were stressing the PT bars. Why?

Were they trying to close a weak interface plane?

If they found a problem in the design (or construction) that required fixing, why they try to fix it without closing the road until the end of construction?

What happened that morning in the meeting that resulted in doing the fix without closing the road?

This is very troublesome. More than before when I thought that they were following the Construction drawings.

If everything is based on the cracks shown in the Feb 18 memo, why they released the PT bars on March 10 to stress them again the day of the collapse? Why they moved the bridge without fixing the problem on the side of the road?

Why a bridge (non-redundant) that is not meeting code or has a problem is allowed to be above traffic from March 10 to March 15? This does not make any sense.

We need to know more. I hope the Miami Herald gets all the info up to the moment of the collapse.

Best regards

RE: Miami Pedestrian Bridge, Part VII

Nothing new there. We may have to wait a year or more. I still wonder who is actually doing the design assessment, as of the 'Party Members' listed, I don't think there is one who is both technically qualified and not conflicted.

RE: Miami Pedestrian Bridge, Part VII

Re: NTSB Preliminary Report May 23, 2018

My highlights:

the propagation of cracks in the region of diagonal member 11

Department of Transportation Office of the Inspector General (OIG)

Miami-Dade Police Department (MDPD)

Lack of detail in report and OIG involvement (if not routine) indicates to me there is a strong criminal element being investigated.

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

RE: Miami Pedestrian Bridge, Part VII

That NTSB Preliminary Report isn't worth the digital footprint it makes. The Pre-lim Report leads one to believe no work was carried out on the number 2 member but evidence of light chipping debris immediately outside the blister suggests otherwise, along with statements from other parties involved. Why isn't Bolton-Perez and Associates Consulting Engineers included in the list of parties assisting in the investigation? Bolton-Perez and Associates Consulting Engineers should have done a better job of documenting the cracks.

RE: Miami Pedestrian Bridge, Part VII

I sure hope the final report is better... this was a total waste.

Dik

RE: Miami Pedestrian Bridge, Part VII

2
I've read hundreds of full NTSB reports, and thousands of preliminary reports and report synopses, and this one is exactly in line with my expectations based on their past work. Their preliminary reports are never anything more than an expression of the facts available by inspection, and where practical, a statement of what resources (if any) are expected to be engaged in the ensuing investigation. They often contain substantial errors and omissions, and are rarely emended before the final report is released.

NTSB final reports are almost always of a depth commensurate with the seriousness of the accident at hand. For a non-fatal small airplane crash, the final report will usually contain only a little more than what was in the preliminary, plus a statement of probable cause. For a fatal airplane crash, the report will be quite voluminous, and may include recommendations for regulatory change in addition to the probable cause. For an accident such as the one at hand, I think we can reasonably expect that the final report will be quite thorough, will engage all necessary resources, and will evaluate a wide range of contributing factors in arriving at a probable cause.

--Bob K.

RE: Miami Pedestrian Bridge, Part VII

Quote (epoxybot (Structural))

Why isn't Bolton-Perez and Associates Consulting Engineers included in the list of parties assisting in the investigation?
Thank you for pointing that out, I missed it. What makes it seem really weird to me, is that the photos and drawing are credited to them?

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

Maybe we won't have to wait so long after all. "In the next month, the NTSB will be..." Typo maybe?

While learning the results and recommendations of the investigation will be interesting, I'd much rather see what they decide to build in place of the failed project.

RE: Miami Pedestrian Bridge, Part VII

Something in steel, I think, Retiredat46.

RE: Miami Pedestrian Bridge, Part VII

I think it would be sensible to put up a precast double tee bridge, as is commonly done to provide pedestrian access to properties that are otherwise isolated by new expressways. There seems to be a common or semi-standard design, supported by two or three hammerheads, terminated by spiral ramps or stairs, and completely covered by chain link fence.

That 8 foot tall 'projectile barrier' or whatever they call it in the plans is just silly. FIU no doubt has multiple students of both sexes who _could_ loft a bowling ball over it with ease. ... and at least an equal number of local nonstudents and random miscreants who _would_ do it, for no particular reason.

Mike Halloran
Pembroke Pines, FL, USA

RE: Miami Pedestrian Bridge, Part VII

Interesting pre-move local news video not yet seen on this thread. They refer to FIU bridge as largest pedestrian bridge in U.S. history. Note two possible safety violations at 46 and 51 seconds.

https://www.nbcmiami.com/on-air/as-seen-on/Pedestr...

RE: Miami Pedestrian Bridge, Part VII

I would hate to be in a wheel chair and use either of those bridges. That's probably why similar designs lost.

RE: Miami Pedestrian Bridge, Part VII

In case people didn't see this, NTSB released a 4 page preliminary report. That report confirms something important that had seemed an open question, that the PT rods in #2 and #11 were indeed de-tensioned on schedule on March 10 when the span was put into place. The activity taking place on March 15, the day of collapse, was not part of the construction plan, and involved adding tension to those rods.

https://www.ntsb.gov/investigations/AccidentReport...

RE: Miami Pedestrian Bridge, Part VII

<tangent>
Thanks to an accidental collision with a trailer ball that I had just installed and immediately forgotten about, I spent a month in a wheelchair with a bum knee.
I found that the ADA guidelines are not comprehensive enough or strict enough.
- The allowable ADA slope is still _very_ difficult to navigate in a self-propelled wheelchair.
- Conformant bathrooms are equipped with wide doors, with very stiff closers that make it impossible to open the damn door while sitting in a wheelchair.
- I have already complained about the stutter bumps on grade crossings, that are no longer required, but were not removed, and are still occasionally placed in new installations, probably due to the glacial pace of plan reviews.

Oh. $24,000 worth of progressively fancier imaging attempts finally produced a picture of what you might call a 'spall' if you saw it on a bearing ball, and advice to wait for it to heal itself, which it eventually did. I still carry a cane, not so much for support but for reaching things on high shelves and picking stuff up off the floor.
</tangent>

Mike Halloran
Pembroke Pines, FL, USA

RE: Miami Pedestrian Bridge, Part VII

We already discussed that useless report.

RE: Miami Pedestrian Bridge, Part VII

The construction joint is irrelevant to any matter in issue. If the concrete was in compression at the construction joint, then the concrete would simply have closed up around the joint. If it was in tension, well, concrete has no strength in tension, so all the tensile forces would have to have been taken by reinforcing bars.

RE: Miami Pedestrian Bridge, Part VII

FYE,
Tension, compression...you left out shear. The joint was not normal to the axial force. And then there is bending, which includes all three.

RE: Miami Pedestrian Bridge, Part VII

The critical question is this: what was the amount and configuration of the steel reinforcement in the deck in the vicinity of the #11/#12 joint with the deck. That is the location of the highest shear (and hence tensile) stress in the entire structure. We are being denied any information about this aspect. No drawings shown from above of the reinforcing steel layout. Only reinforcing steel can take the shear/tensile stresses in the deck at that point - and yet, not a single image or diagram of the layout of that steel. The investigators could easily make that information available. Instead, we are being run around the mulberry bush looking at information about pre-tensioning cables which is irrelevant.

RE: Miami Pedestrian Bridge, Part VII

hokie66 -- I did not leave out shear. Shear is simply a combination of tension and compression under various orientations of the Mohr's diagram.

RE: Miami Pedestrian Bridge, Part VII

hokie66 -- bending is also just a combination of compression and tension, acting as a couple.

RE: Miami Pedestrian Bridge, Part VII

The previously posted plans did show the intended steel to reinforce the joint. The part that post-tensioning plays is that it seems to significantly increases the load on that steel and was the triggering activity for the failure. Had the post-tensioning not been done the bridge might have collapsed later for some other reason, or the end of #11-12 might have been braced by the other bridge half and no one would ever have noticed the potential for disaster. I expect the NTSB will investigate all the alternatives.

RE: Miami Pedestrian Bridge, Part VII

FYE,
As you are new to this site, and to this bridge discussion, perhaps you should examine what has been posted before. Maybe you consider that too onerous, but it is the only way you are going to find out about the reinforcement of both types. Don't expect too much more from the NTSB for a year or so.

RE: Miami Pedestrian Bridge, Part VII

Is it standard practice for the entities involved in a project like this to have insurance that would pay for designing and building the replacement for something that fails during construction? Will they have to start all over with obtaining grants or other funding? What are the chances the pedestrian bridge idea will be abandoned altogether? Where do they go from here, and who is going to pay for it?

It would be a real shame to have to wait for the investigations and inevitable court cases to play out (which might take years) before doing anything to fill what was perceived as a pressing need.

RE: Miami Pedestrian Bridge, Part VII

Quote (Retiredat46)

before doing anything to fill what was perceived as a pressing need.

or maybe a politically expedient one. There's no corruption in Florida.

Dik

RE: Miami Pedestrian Bridge, Part VII

Sure, there are insurances involved, but the insurance companies have lawyers too. The bridge might be built in some form before the litigation is finished, but who pays is a great unknown.

RE: Miami Pedestrian Bridge, Part VII

In My (unfortunately not so humble) Opinion, “FIU got gypped as far as an innovative bridge design.”
Many of you are probably already aware of the following:
Please see:
Hybrid Composite Beams - MoDOTvideo (Missouri) - Aug 11, 2011
Part of its Safe & Sound Bridge Improvement Program "Highways for Life" utilizing hybrid composite beams on three bridge projects
and :
the report .pdf

also:

“The documentary presents realization of project „Com-bridge – An innovative bridge made of FRP composites”. In 2015”


SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

3DDave -- could you perhaps direct me to the post in which the reinforcing steel in the deck is disclosed that would accommodate the shear forces set up by the #11/#12 connection to the deck? I have searched through the VII parts of this blog, and cannot locate anything that fits that description. I'd really appreciate. :)

RE: Miami Pedestrian Bridge, Part VII

There are links to the plans. I downloaded them so I don't know where in the thread it was mentioned. The file I have is
"13-Denney-Pate-signed-and-sealed-FIU-bridge-construction-plans.pdf" which Google indicates is available from https://cdn2.fdot.gov/fiu/13-Denney-Pate-signed-an....

RE: Miami Pedestrian Bridge, Part VII

3DDave, look at sheet B-61 in the above link.

RE: Miami Pedestrian Bridge, Part VII

epoxybot: I used to work for Structural Group many years ago. From my understanding, Structural Technologies owns VSL in the united states. VSL, in the United States was purchased by Structural Group in the 90's or early aughts I believe. All of their offices in the United States are denoted as "Structural Technologies" http://www.vsl.com/contact-us.html

I do know at least state side that Structural Technologies provided Labor for Post tensioning. They also had in-house engineers who specialized in it. Though I'm not aware if their office in Dallas was involved in this project.

RE: Miami Pedestrian Bridge, Part VII

RickyTickyTavi - I know Structural Technologies does contract to do work through out the US but they also sell & assemble(mfg) the hardware for other contractors. What I don't know is if they provide engineering services for other PT contractors. What seems to be clear from an email is that while Structural Technologies is permitted to make wide use of VSL logo, which may or may not confuse people as to who they are contracting with, they can't actually identify themselves as an agent of VSL when contracting. Since they really aren't in the business of research & development, they are more of a Hybrid/Turnkey contractor than a True Turnkey contractor.

One certainly has to wonder about the status of the 492 unit University Bridge Residences project. They were suppose to break ground around April/May 2018. The Quonset Hut/Green House was in fact for the housing project. That is, until the project went from a mix of Condominiums & Apartments to just apartments at the beginning of 2018.

Those apartments will add at least a 1000 students crossing Hwy 41/Tamiami Trail. Yet if construction proceeds, then at some point the street crossing will have to be reconfigured to the east side of 109th Ave, to allow for construction of the pedestrian bridge. There will be more pedestrian traffic crossing 109th on both sides of Hwy 41 (Sweetwater & FIU).

On another topic, it seems there is a unwritten but general rule, the FDOT does not record from their traffic cameras. There are two other agencies, that share the Miami-Dade Sunguide Traffic Center. Miami-Dade Metro & the Florida Hwy Patrol, so there is a remote possibility one of them has the traffic cam footage. While there has been discussion of using the traffic cam system for surveillance, there doesn't appear to be any instance of it having been used this way. If & when it does, then surveillance should be a two-way street (Govt watching the public & the public watching the govt). It makes sense that FDOT would not want to record accidents at intersections, since someone might be able to find a flaw in the traffic engineering & there would be a number of requests for vehicular injury accidents in lawsuits.

I'm fairly sure I read some place in the bid documents that the winning Design-Build team was required to obtain Full Replacement Insurance.

RE: Miami Pedestrian Bridge, Part VII

Quote (TheGreenLama)

Now we don't know if they were in fact stressing or destressing this bar at the time of collapse, but as a general rule the anchor location, geometry, and existing detailing is concerning.

NTSB prelim said "On March 10 per the bridge design plans, construction crew members de-tensioned the bridge diagonal members on the north and south ends of the bridge. When the collapse occurred on March 15, a construction crew was positioned on the structure working on re-tensioning the number 11 diagonal member connecting the canopy and the deck at the north end of the bridge.

The 11/12/deck connection from B-61 (pg 86/110) above at 23 May 18 03:36, shows how re-tensioning force would transfer along the deck (adding to dead load force), now that it's confirmed lower #11 rod was being tightened. One photo shows a crack starting along the deck here. Tension on this rod was 280 kips in spec, but rod is rated at 390 kips (per Williams) - is possible they "gave it a little more" if they wanted to close the crack (Tony Pipitone's WLRN interview said ~"the work being done was to address something discussed at that morning's meeting")

Another photo, above at 21 May 18 21:37 fm B-47,72/110, shows better with a rod that attaches deck to diaphragm.. but I don't understand how this worked.. installed after the deck was moved to something in the pier?).
[highlight these time stamps, CTRL-F will show "find", then click arrow to zip up to it.. thanks to SFCharlie for this tip.. works for Windows7 anyway..)

B-46, Pg 71/110 at lower left shows detail for two PVC pipes (labeled 4" I.D. Reinforcement sleeve, through which passes the rod to pier??). There are two on each side - NTSB photos show the deck broke at the outside edge of these PVC pipes. I didn't see such 4" pipes at any other diaphragm connections (there are two pages for each.. labeled Type I at south end of mainspan to Type IV at north end of backspan.. so Type II is at #11/12).

I was searching for deck-reinforcing rebar which epoxybot 21 May 18 18:40 brought up in that photo/angle I'd never seen before... I thought #12 sheared at the deck, but NO! the cold joint held... looks like it broke apart at the top of the (spec'd) 8"x12" anchor plate... looks like ~1.5" concrete behind it, and on 21" wide truss/support, would only have 4.5" on each side of it.

Besides higher stress at #11/12 shown in Toomas's analysis,
https://www.eng-tips.com/viewthread.cfm?qid=438451 , 30 Apr 18 21:20
this area doesn't have much concrete supporting everything that's embedded within it (and an 8" embedded drain pipe below it).

I have some questions about my own montage above.. the duct stayed in the member about halfway down. Will look at it more later. The length matches what's on the ground.
#11 rode up #12 during collapse (can see marks), but ended up east - rebar and PT rod/duct don't look like they "mashed" against 12 as these look about same position as they'd be in the cast member (upper rod's duct is still intact).
I don't think the 1.75" rod "kinked" or bent so much, but was pushed out of the blister as deck fell, as PT rod supported #11 a bit and "eased" it east. At end of Gwideman's loop, #11 is about parallel/resting on deck, and deck is still resting on the pier. Longer slow motion video shows the deck falls after the 10/11/canopy comes down on it - jams against pier, then falls to ground.

RE: Miami Pedestrian Bridge, Part VII

The images below are taken from the reinforcing steel details posted above by 3DDave
https://cdn2.fdot.gov/fiu/13-Denney-Pate-signed-an...
They are taken from pages 86 and 87 out of 110.

They clearly show that the shear steel at the connection between #11 and #12 to the deck is totally inadequate. It hardly makes nominal steel requirement. The person who designed this connection was clueless. No wonder the investigation is being held in secret.


[img ]



RE: Miami Pedestrian Bridge, Part VII

Quote (Retiredat46 (Aeronautics) )

Is it standard practice for the entities involved in a project like this to have insurance that would pay for designing and building the replacement for something that fails during construction? Will they have to start all over with obtaining grants or other funding? What are the chances the pedestrian bridge idea will be abandoned altogether? Where do they go from here, and who is going to pay for it?

I have no details on this particular contract, but it is normal practice on government projects to have a construction surety bond. Liquated damages are usually included in government projects as well. The government agency requires the Contractor to submit a construction surety bond prior to signing the contract.

What is a construction surety bond? A bond is a contract or a guarantee agreement which contains the promise of a third party, a bonding company or surety, to pay a fixed sum if certain acts are not performed. The acts are typically non-performance or non-payment.

The bonding company or surety will be responsible for the dollar value of the contract, plus liquidated damages.

RE: Miami Pedestrian Bridge, Part VII

Quote (bimr)

What is a construction surety bond? A bond is a contract or a guarantee agreement which contains the promise of a third party, a bonding company or surety, to pay a fixed sum if certain acts are not performed. The acts are typically non-performance or non-payment.

I've been involved with a couple of projects where the surety bond isn't worth the 'powder to blow it to...'. A payment like this comes directly from the insurance companies profits, and they will not relinquish this easily.

Because of the 'design build' nature of the project, there may not be a requirement for bonding.

Dik

RE: Miami Pedestrian Bridge, Part VII

Quote (epoxybot (Structural))

Why isn't Bolton-Perez and Associates Consulting Engineers included in the list of parties assisting in the investigation? Bolton-Perez and Associates Consulting Engineers should have done a better job of documenting the cracks.

Bolton-Perez and Associates Consulting Engineers website states that they are providing construction engineering and inspection services.

Bolton-Perez and Associates Consulting Engineers website

In my experience, having the design engineering firm conducting the construction engineering and inspection (instead of a 3rd party) is preferred since the design engineer will know the intent of the various design details and should be able to quickly respond to the questions that will come up during construction.

RE: Miami Pedestrian Bridge, Part VII

Quote (dik (Structural) )

I've been involved with a couple of projects where the surety bond isn't worth the 'powder to blow it to...'. A payment like this comes directly from the insurance companies profits, and they will not relinquish this easily.

Because of the 'design build' nature of the project, there may not be a requirement for bonding.

Your comments indicate that you don't have much experience working under government contracts.

In most cases, bid, performance and payment bonds are required by law on public construction projects.

Virtually all of the public construction work in America is accomplished by private sector firms. This work generally is awarded to the lowest responsive bidder through the open competitive sealed bid system. Surety bonds play a critical role in making the system work.

The Bid Bond is intended to keep frivolous bidders out of the bidding process by assuring that the successful bidder will enter into the contract and provide the required performance and payment bonds. If the lowest bidder fails to honor these commitments, the owner is protected, up to the amount of the bid bond, usually for the difference between the low bid and the next higher responsive bid.

The Performance Bond secures the contractor’s promise to perform the contract in accordance with its terms and conditions, at the agreed upon price, and within the time allowed.

Surety Information

RE: Miami Pedestrian Bridge, Part VII

bimr: The contractor on the Lindsay Police station was terminated for cause (and against my thoughts)... they tried to cash his bond, and, he walked away a million dollars richer.

The steel fabricator for the addition to one of the large shopping centres in Winnipeg made a $300,000+ error... I found it when I was reviewing bids... I usually give a contractor the opportunity to withdraw or honour his bid... the developer insisten that he not withdraw, or the developer would cash the bid bond... and, I've got a few others out there...

I don't know how the contract bonding was handled for the 'bridge', but, because it was a 'design-build' effort, bonding could have been waived...

Dik

RE: Miami Pedestrian Bridge, Part VII

Some things were learned from that test of a concrete truss/beam in lab conditions. But the Miami bridge was a very different thing, mostly because of its cross-sectional shape. What is most tragic in hindsight is that they did not load test the structure when they had it beside the road. It would have been quite simple to do.

RE: Miami Pedestrian Bridge, Part VII

Quote (hokie66)

did not load test the structure

I have a feeling they did not load test it because they had inside knowledge it was not optimal until other span was placed with everything tightened and grouted. Knowing this, they would be afraid of breaking it. But then again, I could be completely wrong in this theory because they did not place short span first. It seems to me the transporter is precise enough to place main next to existing sub span.

I wonder how often they checked defection?

I don't know what kind of test cantilever below is subject to before allowing traffic. Partial load test? I'm not certain this photo is real.

Florida highway:

RE: Miami Pedestrian Bridge, Part VII

It is real. Precast segmental post-tensioned cantilever construction is common, and well tested now by experience. As to how much testing went into the segmental system originally, I don't know. But exactly zero load testing went into the Miami span.

RE: Miami Pedestrian Bridge, Part VII

hokie66,

Thank you for reply. I was feigning naivete and/or being rhetorical (bad habit, need to work on being more direct)... because what really bugs me about FIU bridge is how "non-academic" it was. I can find nothing that builds up to the way this project was done. No precursor designs, nothing similar in the world, no research papers, and like you said, no history of testing this concept at all.

How did this happen? Was it propriety? Have any patents been applied for?

I don't think it qualifies as a hybrid, it's a Frankenstein.

The NTSB will look silly if they do not notice this was a one-off design.

P.S.
Q. Would taking the bridge in my photo above, inverting it and adding viewports be a feasible starting point for conceptualizing a low deck span?

A. No - stick with steel through truss, it's only a pedestrian overpass paid with tax money, if it doesn't last 100 years, build another one.

My intention is not to insult the people involved, I don't think anyone could have gotten that concept to be robust. Their first submission was almost certainly sound.

RE: Miami Pedestrian Bridge, Part VII

I maybe in a minority, but, I thought the original design was attractive, and, an interesting engineering design problem. I also think the cable stayed members should have been incorporated into the design. With the 'slender I-beam/truss' configuration, the lateral torsional stability would have been a major design issue.

Dik

RE: Miami Pedestrian Bridge, Part VII

Please post a picture or link for the original design.

RE: Miami Pedestrian Bridge, Part VII

Were the pylon vertical PT rods installed through the deck? Photos of No.11 and 12 node appear to show the PVC pipes extend above the deck indicating the PT extension bar, PT back plate, and nut have not been installed.
Dwg B-46 and B-47 show four 4" ID reinforcement sleeves for 1-3/8" PT bars, two each side of No. 12.
Pylon details, Dwg B-23 appear to show only two 1-3/8" PT bars, with 4'-0" embedment
The four PT bars do not appear in the PT schedule, Dwg B-69.
Stage 3 of erection sequence, note 4, calls for pylon PT bars to be stressed, Dwg B-109

RE: Miami Pedestrian Bridge, Part VII

Quote (Retiredat46 (Aeronautics)26 May 18 15:41)

Please post a picture or link for the original design.
8EngineerEIT (Structural) - 16 Mar 18 15:04 Posted this info.
I use control-F to search for the "time stamp"(16 Mar 18 15:04) within the thread

RE: Miami Pedestrian Bridge, Part VII

Quote (dik (Structural)26 May 18 14:36)

I also think the cable stayed members should have been incorporated into the design.
Do I understand correctly that you're suggesting real cables instead of pipes?
Thanks,

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

The bridge in that link looks like what they were building.



I thought there was an original design I hadn't seen before. I did run across this design in my earlier searching. It's certainly more attractive, and it has real cables.




RE: Miami Pedestrian Bridge, Part VII

A cable stayed bridge might have closed the road for months. It might also have collapsed as the Colombia bridge did, for similar lack of appropriate design and analysis work. Just like the steel structures in the Hyatt Regency and the I-35 bridge.

Looking solely at the gross form or material choices of this bridge as an indicator of potential for failure skips investigating how the design and approval process was able to miss the flaw in this structure.

I suspect that the NTSB will find a nearly incandescent omission in the stress analysis - a clear lack of consideration for, or underestimation of, the shear retention between #11 and the deck and the aggravation of that shear by the use of post-tensioning. I suspect they will also find a lack of an independent analysis; perhaps there was a check of an originally flawed approach that confirmed the work that was done was done correctly while failing to note areas that were missed or assumptions that were incorrect, but not truly independent.

What I look forward to is an examination of the design and analysis process and some recommendations about how missing this detail could have been avoided.

RE: Miami Pedestrian Bridge, Part VII

The long span of a cable-stayed bridge could be made with six nearly identical sections built nearby. After building the support structures and the short span, the six sections of the long span could be moved into place and supported with the cables one after the other in several days. Not as dramatic as moving a one-piece span, but certainly doable. It would show off the benefits of ABC, too.

RE: Miami Pedestrian Bridge, Part VII

jrs87,

I completely agree with your post, at least everything above the P.S. This was not a matter of just tweaking some numbers incorrectly. The concept was flawed irreparably. The NTSB, as many in these threads have done, may dwell on one connection, but if so, they will be missing the forest for the trees.

RE: Miami Pedestrian Bridge, Part VII

Anyone familiar with NTSB reports would never say they dwell on one thing and miss any forest.

Edit to add: Unless the forest has been so thoroughly explored as to be familiar to everyone. Not much need to emphasize that aircraft need to have enough fuel for the entire flight and other such observations.

RE: Miami Pedestrian Bridge, Part VII

That may be the case in aircraft, but in bridge failure investigations, not so much. We will see.

RE: Miami Pedestrian Bridge, Part VII

Hokie66 - the NTSB recently released a report on a fire in a RoRo ship that was traced to the lack of a followup on a vehicle recall notice that was issued a decade before. They do more than airplanes.

RE: Miami Pedestrian Bridge, Part VII

Quote (SFCharlie)

that you're suggesting real cables instead of pipes

It doesn't matter, either can work. It's a matter of detailing the connection.

It collapsed for other reasons.
Dik

RE: Miami Pedestrian Bridge, Part VII

We have seen the NTSB will risk life and limb in an investigation. I personally would have been very wary of being near that bent PT bar. Perhaps they checked with VSL first. Let's not forget the OIG also is conducting an investigation.

A rewatch of this video is worthwhile: https://www.facebook.com/tampabaynews/videos/10156...

They will document emergency response and how crushed vehicles absorbed crash [crush] energy. Perhaps they will even note how the giant air lift bags were not effective here.

RE: Miami Pedestrian Bridge, Part VII

3DDave,
I know they investigate all types of transport calamities. But I am most interested in bridges, and they have investigated many, most times with assistance from outside consultants. I hope they have the right folks involved this time.

RE: Miami Pedestrian Bridge, Part VII


Quote (dik (Structural))

I don't know how the contract bonding was handled for the 'bridge', but, because it was a 'design-build' effort, bonding could have been waived...

Here is an example of a design build performance bond that MCM used on another contract. The State of Florida has a copy of the performance bond.


Example of FDOT Design build Performance Bond with MCM:

Example of FDOT Design build Performance Bond with MCM
of

FDOT Design Build Info

There is no way that MCM is going to walk away from this.

RE: Miami Pedestrian Bridge, Part VII

Things were definitely learned from those collapses, but I doubt there is anything directly applicable to the Miami footbridge.

RE: Miami Pedestrian Bridge, Part VII

jrs87,

In the sense that the problems were in the connections, both the Hartford failure and Bill LeMessurier's averted strength deficiency are classic examples.

The Hartford space frame was a case of axial members not meeting where the analysis required, and that bears some similarity to the Miami collapse.

The CitiCorp Tower may have survived without the modifications. We will never know, but LeMessurier took the right and ethical action, and he is respected in the structural community because of it.

RE: Miami Pedestrian Bridge, Part VII

Quote (hokie66 (Structural))

26 May 18 20:14
That may be the case in aircraft, but in bridge failure investigations, not so much. We will see.
please search for "i35 ntsb"
I count six releases by the ntsb, including a fifth update.
The "Accident Report" alone is 178 pages (Yes I'm counting the covers).
That's about the size of our first three threads:
Miami Pedestrian Bridge, Part I thread 815-436595
68 Pages
Miami Pedestrian Bridge, Part II thread 815-436699
55 Pages
Miami Pedestrian Bridge, Part III thread 815-436802
67 Pages

They not only identify gussets that were not revised during a design change, but have a photo of the gusset bending during a pre accident inspection.
The "Accident Report" will probably take a long time, because there is so much to dig into, as we have noted here.
Thank you and Thank you all for maintaining this forum, and all yourinsights and cross check and explanations,

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

I may be naive, or worse, but aren't there remedies for cracks in structural concrete, Fiber reinforced polymer wraps?
Couldn't they have used a sample hole saw to drill through the top face of the deck at the 11-12 joint and filled it with something very strong (steel or Fiber reinforced concrete, ?). ...epoxied a steel pin in the hole?
With all the pre and post tensioned precast concrete being installed, there must be industry accepted repairs?

SF Charlie
Eng-Tips.com Forum Policies

RE: Miami Pedestrian Bridge, Part VII

SFCharlie,
Yes, I agree that the I35W report was extensive. That one had as much discussion on this site as the Miami bridge.

There are industry accepted repairs for many types of defects in concrete structures. But this failure, although it should have been anticipated, was unprecedented because the concrete truss form of the bridge was itself unprecedented. The other concrete truss examples which have been posted here bear little resemblance to the Miami attempt. Perhaps that is why the cracks were not assessed as serious enough for concern.

RE: Miami Pedestrian Bridge, Part VII

Quote (hokie66 (Structural))

Perhaps that is why the cracks were not assessed as serious enough for concern.
I'm afraid you're probably right. In the Missouri example I posted above, they found their assumptions were wrong because they instrumented the bajesus out of it. They learned from it, and got a cheaper and much lighter bridge. Again, why wasn't FIU eager to learn and have their students learn from their adventure into innovation?

Thank you for replying to my questions,

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

Following up on the idea that concrete truss bridges are unprecedented, in fact most of the true cable stayed bridges that Figg has designed utilize essentially a concrete truss spanning transversely across the bridge deck. They pioneered the single cable plane design and use concrete “delta frames” to transfer loads in twin box spans to the central stays. See page 4 at the below link for a section of the C&D Canal Bridge which is typical of Figg cable stayed spans.

Link

However these true cable stayed spans are all hyperstatic unlike the FIU single truss design.

RE: Miami Pedestrian Bridge, Part VII

I beleive a concrete single axis I-beam bulb truss does not have optimal section-moment-of-inertia: https://skyciv.com/tutorials/calculating-beam-sect...

RUStructural, your link for Pate article proves my point, where are similar articles on the FIU design? I could be wrong, but I don't think design concept was motivated by innovation, FIGG/MCM was simply trying to come up with something to satisfy the selection committee. This in and of itself of course is not unethical.


RE: Miami Pedestrian Bridge, Part VII

I haven't been following this thread for the past month or so. Do we know what happened yet? Do we know what failed?

RE: Miami Pedestrian Bridge, Part VII

Quote (Tomfh (Structural))

Do we know what happened yet? Do we know what failed?
We have refined, incrementally, what we think happened, Nothing that was not hinted in Part 1.
The NTSB issued a Preliminary report with only info we had already found and posted here.
One thing they did clarify is that the PT rods at 1-2 and 11-12 were Detentioned on the 10th of March and REtentioned on the 15th at the time of the collapse.
But no, we don't know what failed, and it's not the style of the NTSB to state cause until the Accident report, probably in about a year from now.
Regards,

RE: Miami Pedestrian Bridge, Part VII

jrs87,

Not sure about the moment of inertia being inadequate, the span to depth looks quite reasonable considering the relatively light nature of the live load but I’ve not made any numbers. My intent was to provide some additional background on concrete trusses, not to defend the concept. It seems to me that the design firm did have some experience with concrete trusses and that the concept was not completely untested.

RE: Miami Pedestrian Bridge, Part VII

2
Simple but interesting paper on bridges:

Go to page 135/169 first.

Chase, Cody, "A Look at Bridges: A Study of Types, Histories, and the Marriage of Engineering and Architecture" (2015).Architectural Studies Integrative Projects.Paper 73. http://digitalcommons.conncoll.edu/archstudintproj...

RE: Miami Pedestrian Bridge, Part VII

RUStructural - Live loads is something that has bothered me from the start of this thread. The concept of this Signature Bridge as a Place to linger and meet up with people; a public space. I have visions of the bridge lit up in various colors at night & a couple hundred celebrating, drunk & rowdy college students jumping up & down to music. I think building a bridge as a public space adjacent to a university that isn't built to stadium/arena live loads is just asking for a disaster. While the likelihood is small, I don't think such a circumstance can be discounted as inconceivable.

RE: Miami Pedestrian Bridge, Part VII

epoxybot,
But live load didn't have anything to do with the collapse.

RE: Miami Pedestrian Bridge, Part VII

Live load due to "a couple hundred celebrating, drunk & rowdy college students jumping up & down to music" is >> Live load due to "Pedestrians" isn't it?

STF

RE: Miami Pedestrian Bridge, Part VII

Probably not, SparWeb, but the impact and vibrations would have to be considered. But I doubt that scenario was contemplated, and the University could undoubtedly provide better venues for that type activity.

RE: Miami Pedestrian Bridge, Part VII

I just came across this old article on the Chronicle of Higher Education: Link. It does appear that FIU dictated the overall design of the bridge that probably sealed the fate of the bridge from the beginning. According to the article, FIU wanted it to be cable-stayed for its looks (opting for aesthetics over safety?). It is not clear why they ended up with a truss bridge with decorative cables. Then they also decided to go with the heavy and fragile concrete over the lightweight, cheaper and safer steel. The irony is that the researcher in the article actually specializes in steel bridge, but chose to give concrete a shot for both aesthetics and longer service life. According to the article, the researcher had just finished a major project on bridge service life and wanted to use the bridge for experiment and to verify research results (re the last paragraph of the article). Perhaps the final nail in the coffin was FIU's decision to also use the ABC method advocated by the researcher. Combining ABC with the long, heavy and fragile concrete slab may have turned a usual over-engineered bridge to one that was under-engineered in terms of withstanding construction/design errors. Shouldn't experiments belong in labs? Sadly, these decisions may have cost six lives.

RE: Miami Pedestrian Bridge, Part VII

The AASHTO pedestrian bridge live load is 90psf nominal and gets a 1.75 load factor for 158psf factored LL. To get that density of people no one will have space to jump or really move at all.

RE: Miami Pedestrian Bridge, Part VII

Quote (jrcooper80 (Civil/Environmental))

(opting for aesthetics over safety?)
Thanks for finding this.
Please see my reply (26 May 18 23:42) to Retiredat46 (Aeronautics) 26 May 18 17:10 above.
The link is to an article in FIU Magazine reaffirming your analysis.

Quote (use the bridge for experiment and to verify research results)

Yes, but aren't experiments supposed to have criteria and instrumentation and findings?

RE: Miami Pedestrian Bridge, Part VII

NTSB releases preliminary report

Link

RE: Miami Pedestrian Bridge, Part VII

of course it doesn't say much.

RE: Miami Pedestrian Bridge, Part VII

Not sure if NTSB error, but the prelim report said the photos were from 2/24/18, but the created date of the six photos was 2/28. The accompanying Crack Report memo from Jose Morales was also dated 2/28 and just noticed that Carlos Chapman was copied (the worker on canopy who latched his harness before it fell), so maybe he was a senior guy w/Structural Technologies.

Problem is they had warning that something was wrong (per cracks) 10-14 days before they moved the span and nothing was said until after the move. Before moving, the span was supported only at ends as it would be on the piers, so they could have done 'real world' tests/adjustments. Many here say the 11/12/deck connection was weak, Toomas Kaljas ran FEA that showed high 3D stress there, but no one's estimated the strength of the connection (maybe not so easy). The 1/2/deck connection held after the collapse, as did vertical #1, LONG members 4 (no PT rods) and 2 held, but member 3 had much damage even though it was ~vertical - just correlated this with being the only other member with odd/high 3D stress.


Warning signs were missed/ignored. Is similar to the Hartford Civic Center where bending of girders was evident on the ground, but they hoisted up the sections and continued building. And like the WestGate Bridge, they didn't clear out underneath while working on it - Wikipedia said "Many of those who perished were on lunch break beneath the structure in workers' huts, which were crushed by the falling span." (this after they'd put 80 tons on it and had removed 37 bolts to change camber/match sides).

RE: Miami Pedestrian Bridge, Part VII

I expect that when tension was applied to #11 as part of the move it eased back on the crack and then when the post-tensioning was relieved the joint opened again; so they thought that re-applying the tension would close the crack.

In the pictures in the FEA stress analysis, the diagonals should all end flush with the top of the deck as the deck was poured first and only re-bar and friction was holding the diagonals in place. The stress analysis does not show the finished size of #2, which nearly doubled in depth and probably accounted for its survival.

RE: Miami Pedestrian Bridge, Part VII

Would it have made any difference if they had made a raised pedestal as part of the deck pour below 11 and 12 so the construction joint on 11 would have been perpendicular to the axis of 11? I'm assuming no change to the rebar placement. The bottom of the pedestal would still see significant shear, but at least it would be one solid piece of concrete.

I'm just really bothered by a construction joint passing at an angle through the area with the highest loading. Is that an unjustified concern?

RE: Miami Pedestrian Bridge, Part VII

Here is Boston Big Dig Tunnel Ceiling panel collapse litigation compass rose.
Two people were killed: driver and passenger of car the panel fell on.
The courts and officers of the court (lawyers) took two years to get to
the bottom of it. By process of elimnation, the supplier of the adhesive
for the ceiling anchors was held responsible, although they claimed it was
the field contractor who mishandled the adhesive who was responsible.

So, Hokie66 nailed it. With the list of cast of suspects already growing, and without an obvious cause-effect chain discovered, it will take a while.

RE: Miami Pedestrian Bridge, Part VII

CCW1 - I don't think a process of elimination in the courts actually defines who is principally responsible unless the actions taken were done so without any knowledge of the parties producing the materials & assembly. Both SIKA & Power Fasteners should have shut down any consideration of using an adhesive for suspending concrete panels over any area that humans might pass under or anywhere that might create an attending hazard to structures/infrastructure. They are suppose to be the experts on adhesives. Not the engineers, the suppliers or the contractors.

This is when companies like SIKA & Power Fasteners are suppose to say, "You can't do that and even if you decide to do it, we will not supply the material" and then you follow up with a letter making your declaration clear. Things have changed a lot since the cost of ICBO Reports have eliminated a lot of very good adhesive manufacturers from anchoring applications. There is a much smaller circle of input as to what is an acceptable risk. Hilti has done a great job of specializing the adhesive anchor business and deserves their reward for doing the R&D. The companies in the adhesive anchor business today enjoy limited competition and should find it easy to JUST SAY NO to request for an overhead applications. If hundreds of adhesive manufacturers would not allow it (and didn't), there isn't any better thinking that applies to overhead/suspended adhesive applications now ICBO has entered the game.

Prior to the Big Dig the only applications that I was aware of where adhesive anchors had been used in overhead/suspended applications, was for temporary rock screens in mining & tunneling work. From the point of conception for this work on the Big Dig, it is the adhesive manufacturers who knew they were treading where other manufacturers would have stopped. Having worked for a former Chairman of ACI Committee 503 & a former Chairman of ASTM C-881, if I had walked the question of the use of adhesives to suspend the concrete panels on the Big Dig Tunnels, to either of their office doors, they would have responded with a definitive NO. In my personal judgement I find SIKA & Power Fasteners participation contemptible. More so since like most manufacturers, they should have known the frequency of how often installation via cartridges with static mixing elements were poorly understood & executed by ordinary tradesmen, at that time.

RE: Miami Pedestrian Bridge, Part VII

Hear, hear, epoxybot.

RE: Miami Pedestrian Bridge, Part VII

Big Dig was the black hole granddaddy of all public works projects that formed over the northeast seaboard 1992-2007 (for the youngsters here). Everything associated with it was ground breaking, new technology on a scale never done before. You can read about it from many sources, maybe in your text books by now. Here is just one https://www.nasa.gov/pdf/469423main_ASK_39s_big_di.... Probably some of the folks on here worked on the project, something for everybody including engineering the widest cable-stayed bridge in the world, at the time.
Excerpt:
Boston’s Central Artery/Tunnel Project, commonly known as the Big Dig, was the largest, most complex, and most technically challenging highway project in American history. Larger than the Panama Canal, the Hoover Dam, and the Alaska Pipeline projects, it was built through the heart of one of the nation’s oldest cities. Its list of engineering firsts include the deepest underwater connection and the largest slurry-wall application in North America, unprecedented ground freezing, extensive deep-soil mixing programs to stabilize Boston’s soils, the world’s widest cable-stayed bridge, and the largest tunnel-ventilation system in the world.

One of the photographs in the reference shows the flat roof of the 10 lane tunnel ceiling, also a photo of the big Bunker Hill Cable-Stayed bridge.

Epoxybot do you know if they went back and replaced all the adhesive anchors on the ceiling panels or what?

RE: Miami Pedestrian Bridge, Part VII

Speaking of Impact and vibration criteria. How would AASHTO LRFD Section 3.6.5 apply to this Miami Ped. Bridge?

RE: Miami Pedestrian Bridge, Part VII

CCW1,
We had an extensive discussion about the Big Dig ceiling failure when it happened, and looking back, that was 12 years ago.

My recollection is that all the ceiling hanging bolts were replaced or supplemented with Hilti mechanical undercut anchors.

RE: Miami Pedestrian Bridge, Part VII

Nothing new here. Just wanted to get a better picture of the FIGG design team. Denny Pate was the engineer of record, but others help craft this hybrid. Pate stamped the drawing. He's responsible. But it doesn't mean he designed the bridge. This was a team failure. These were cut from the "MCM FIGG Proposal for FIU Pedestrian Bridge," 9-30-2015 [Link].
>>

>>

>>

RE: Miami Pedestrian Bridge, Part VII

I notice FDOT is missing from the chart...

Dik

RE: Miami Pedestrian Bridge, Part VII

Quote (Hokie66)

My recollection is that all the ceiling hanging bolts were replaced or supplemented with Hilti mechanical undercut anchors.

You're recollection is good... problem came about because they 'switched/substituted' the epoxies and used a quick setting one that had 'creep' characteristics. I agree with the use of undercut anchors. We had a really good discussion with the local Hilti rep. He was surprised the office was aware of the Big Dig.

Dik

RE: Miami Pedestrian Bridge, Part VII

https://www.db-bauzeitung.de/allgemein/ulrich-fins...

Quote from link above, translated by Chrome from German to English:

In 1933, a hangar collapses in Cottbus. Finsterwalder comes in custody, is interrogated and threatened with death penalty for sabotage. Since the inspection of the statics and construction confirms the perfect quality of the planning and execution, it [he] is released. One seeks and finds the error in the creeping of the concrete, the effects of which had not yet been taken into account in the state of the art [4].

RE: Miami Pedestrian Bridge, Part VII

jrs87

Finterwalder, and the future engineers that learnt from his work, was very lucky. Remmember, that was nazi Germany.

An additional history fact, Freyssinet had already learnt about the effects of concrete creep when his Veurdre bridge (1910) starting sagging. At the time, he had to go at night with his trusted foreman to jack appart the three-hinge arch at the crown. Later on he built a test arch to study the effect of creep in concrete bridges. It was his knowledge of creep that allow him to develop a working concept of prestressed concrete. Previous developers did not fully meet the goal because of the creep, shrinkage and steel relaxation.


Live long and prosper

RE: Miami Pedestrian Bridge, Part VII

The Mad Spaniard,

Being a mechanical engineer, I don't remember names Finterwalder and Freyssinet. I found Finterwalder today by accident. I'm impressed by him.

After examining details of Mangfall Bridge, I'm curious why FIU bridge design deviates.

Mangfall Bridge:

http://casce.princeton.edu/Resources/lecture-previ...

RE: Miami Pedestrian Bridge, Part VII

jrs87,

Another name you should become familiar with is T.Y. Lin. By the way, those were some interesting lecture notes.

Here's a picture of T.Y. Lin's Ruck-a-Chucky bridge, arguably the most famous bridge never built.

Link

RE: Miami Pedestrian Bridge, Part VII

The designs of Robert Maillart may provide some insight into best ways to approach concrete truss. It seems engineers in his time faced much more skepticism from the public than now. Perhaps the public now feels the government is watching out for them...

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

RE: Miami Pedestrian Bridge, Part VII

2
Anyone speak Polish who can translate this? Illustrations look great, anchor at 11 is very interesting. No spiral confinement, no appreciable anchor steel reinforcement. Clean of concrete, a very explosive break. Anchor was to be designed by the PT supplier in the local zone behind the anchor so the plans showing nothing on this.

https://youtu.be/znzCubAWIeo

Regards,

Mojojohn

RE: Miami Pedestrian Bridge, Part VII

Quote (3DDave)

I expect that when tension was applied to #11 as part of the move it eased back on the crack and then when the post-tensioning was relieved the joint opened again; so they thought that re-applying the tension would close the crack.
From report (after 2/6/18 inspection), the cross-sectional ~0.004" cracks on #3 and #10 appeared after #2 and #11 were stressed the first time (shoring still in place) - report said there were no other similar cracks.

The 2/28/18 report said #1/2 and #11/12 larger cracks appeared after shoring was removed, but before span was moved. This report was sent to Rodrigo Isaza at MCM and others, but not Denney Pate.. though it said "Forward to the EOR for their information. We will monitor these or any other developing cracks on the bridge, but we would like to the EOR to provide a response and determine if these were expected during the bridge stressing" so he should have gotten it.

From news, etc, it seems nothing was done, except to "wait and see" what happened after moving the span.

Pre-tensioning was relieved 10 days later, as scheduled, after moving the span (I agree cracks would get worse - from "jostling" during move and releasing #11 tension). Within a couple days Denney Pate left the phone msg to FDOT about the cracks which was retrieved Friday after collapse, but there was a mtg Thursday morning (assumed) to discuss the cracks with decision made to re-stress #11 to close them. The msg to FDOT was thought to be when cracks were first noticed, but the "leaked" photo/memo showed otherwise.

What happened actually proved ABC is better. The problem was seen before the span was moved. With span supported only under diaphragms (as in final position), there was opportunity to evaluate the cracks, de-stress #2 and #11 (as was planned after moving), and re-stress on side of road (attempt to close cracks). Also could have load tested in a safe place (though this would take more time and money). Had this design been used without ABC, the same thing would have happened, but there would have been no opportunity to deal with it away from traffic.

RE: Miami Pedestrian Bridge, Part VII

2

Quote (MOJOJOHN (Structural))

Anyone speak Polish who can translate this?
YouTube speaks Polish:
While viewing the video in your browser:
pause it
just to the right of the "like" and "dislike" thumbs; are three dots ...
click on the dots and select "open transcript" A box with the scrolling transcript will appear (will be in Polish).
Move your cursor to a blank area outside the box and Right click and select "Translate to English"
play... for me the on screen captions are now in English.

What a beautifully drawn and presented video!

Thank you for finding this

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

tkjohnson,

Re: Links

What is going on in Florida? Great finds.

RE: Miami Pedestrian Bridge, Part VII

SFCharlie: thanks for the info. My computer (old laptop/windows7) wouldn't give the right click option for "translate to english" but I got through it and maybe this works (but I couldn't make it full screen).
https://www.youtube.com/timedtext_editor?action_md...
THANKS MOJOJOHN! best I've seen and he did it with prelim specs.

RE: Miami Pedestrian Bridge, Part VII

SF Charlie,
Thank you for the instructions on YouTube video translations. I didn't know you could do that.
Works very well for the most part. I like this translation though. Ha!

RE: Miami Pedestrian Bridge, Part VII

Any ideas on what marking on this sensor may be? Also, what could have caused scorch marks?

P.S.

This video makes a point that MCM may have been faced with need to destroy span and restart and they could not face it. Can anyone cite a project that was destroyed and rebuilt as a precaution? I feel that the managers of any project MUST be prepared to abort. You can even test for this, but I will not go into that, use your imagination. The video is professional and excellent. Good find.



RE: Miami Pedestrian Bridge, Part VII

Quote (TheGreenLama (Structural))

Nothing new here. Just wanted to get a better picture of the FIGG design team. Denny Pate was the engineer of record, but others help craft this hybrid. Pate stamped the drawing. He's responsible. But it doesn't mean he designed the bridge. This was a team failure. These were cut from the "MCM FIGG Proposal for FIU Pedestrian Bridge," 9-30-2015

Does anyone else think it seems odd that Ms. Figg is not licensed when she is in charge of the bridge engineering business. In fact, many of the players on the project are unlicensed so they don't have to worry about losing their licenses.

RE: Miami Pedestrian Bridge, Part VII

More FIU Bridge background documentation, RFP etc
I think I saw some discussion of the RFP before, but I do not remember the images of "Examples of Signature Pedestrian Bridge Design Concept Precedents". Maybe I'm just being forgetful. I'm sure some are duplicates, so I apologize to any who's toes I've stepped on.

fiu-db-rfp-maxprice_draft_2014-06-24_final.pdf

FIU-Pedestrian-Bridge-Design-Criteria-2015-05-06_REV.pdf

white-house-honors-fiu-bridge-expert-as-champion-of-change

federal-grant-to-boost-universitycity-a-transportation-hub-at-fiu

building-bridges-to-the-white-house

chronicle-of-higher-education-engineer-connects-his-research-with-campus-bridge-project

fiu-to-develop-technology-to-fix-and-build-bridges-fast

UniversityCity_Project-Conceptual_Plans_2014-06_FINAL.pdf

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

Quote (JG2828)

I like this translation though
I can only imagine the aesthetic appreciation of bathtubs by the university students.
Thanks

SF Charlie
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RE: Miami Pedestrian Bridge, Part VII

Quote (bimr)

Does anyone else think it seems odd that Ms. Figg is not licensed when she is in charge of the bridge engineering business. In fact, many of the players on the project are unlicensed so they don't have to worry about losing their licenses.

Not especially. Lots of companies doing licensed work have CEOs who aren't.

RE: Miami Pedestrian Bridge, Part VII

SFCharlie,

One thing this background information shows is that safety was not the primary motivation of this project, real estate development was. If safety was primary, FIU would not have waited years to build signature bridge, they would have built lower-cost bridge to solve problem of safety in a timely manner. After all, the other side of the connected FIU parking structure has an existing regular pedestrian overpass. But then again, my argument falls apart because despite accident last year, there does not appear to be a need for a bridge. In other words, where is video of hoards of students crossing this road?

So, the bridge may be necessary for future development of a real estate deal. How is it TIGER was used to pay for an amenity of a future project?

None of this proves anything related to cause of collapse, except it may show evidence of bait-and-switch.

I feel Atorod Azizinamini deserves benefit of doubt here at this point.

RE: Miami Pedestrian Bridge, Part VII

Scorch marks on 12 are likely from cut of of pt tendons with a torch.

RE: Miami Pedestrian Bridge, Part VII

Ms. Figg is Eugene Figg's daugter. Figg was a well known bridge engineer.

RE: Miami Pedestrian Bridge, Part VII

Miami-Herald is still pushing to get records released. Judge "Cooper refused to dismiss the case and instead gave federal investigators two weeks to decide whether they want to defend themselves in a Florida courtroom before he rules." Interesting that the author said cracks were noted "just days" before the collapse, instead of referring to photos from 2/28.
http://www.miamiherald.com/news/state/article21248...

RE: Miami Pedestrian Bridge, Part VII

Quote (jrs87)

I feel Atorod Azizinamini deserves benefit of doubt here at this point.

Well, from what I have read, and in his very own words (see Link), he appears to be the person who shaped the FIU bridge. If they had simply gone with a steel bridge, i.e., if they truly care about safety, I believe all six victims would still be alive today. If he was not involved, why was he the only technical person quoted when the bridge was first installed? (see Link). Or was he simply trying to take the spotlight/credit for a bridge he was not a part of?

I think people should not just dismiss the high cost of the bridge (over $10M). When an unnecessarily expensive project got built, elsewhere in our roadway system that could make better use of the money to actually save lives had to give. Also remember that FIU is a public university supported by the taxpayers and their mostly poor student population (many from poor immigrant families). It has no business building fancy structures, especially as a giveaway to real-estate developers in this case. Simply because they could use their political might of South Florida (Marco Rubio, Debbie Wasserman, etc.) to get the project funded does not mean they should do it.

RE: Miami Pedestrian Bridge, Part VII

Quote (dik)

I notice FDOT is missing from the chart...

That's why FDOT and the governor have said all along it was a FIU project. Over the years, FIU has grown very powerful politically. The engineers at FDOT were no match for the well-connected FIU administration politically.

RE: Miami Pedestrian Bridge, Part VII

jrs87
My gumboots weren't tall enough, so I now have to throw them away. And my feet stink.

RE: Miami Pedestrian Bridge, Part VII

jrcooper80... it depends on FDOT's involvement... they may say they had none, but, if they were attendants at all site meetings and were on the list of people to be copied or contacted... the lawyers will have a hayday.

Dik

RE: Miami Pedestrian Bridge, Part VII

https://www.dropbox.com/sh/u8qicuu22xmfhg1/AAABWOf...

I think he is Kenneth Jessell. The story I heard was that their first two TIGER applications were not successful because the project B/C ratio was below 1.0. The firm that did the B/C estimation was asked to find ways to increase the b/c. They made up some accidents that did not exist. Except for the one pedestrian fatality that happened last year, which was long after the bridge was approved, there had been no pedestrian accidents at the location. That was what I heard. My source could be wrong. I think there ought to be a criminal investigation.

RE: Miami Pedestrian Bridge, Part VII

This is something that's been bothering me for a while:


In all instances the longitudinal reinforcement extending from the truss diagonals into the bottom slab and top canopy terminate in a "J" bend rather than an "L" bend. Plus, they often appear to terminate above the outside face slab reinforcement, and are without any crossing bars at the bends. It seems trivial, but it's not. I would think you'd want to securely anchor these within the top and bottom chords and tie the two together. Why was it done this way? Could the designers have wanted to in some way try to simulate a steel truss-like effect in a concrete truss? No answer on this one.

It's little things like this, along with the minimal amounts of mild steel within the structure, the odd stressing sequence, the work point locations for 1/2 and 11/12 being so close to the end of the bridge, to name just a few, that makes me wonder what post-tension, concrete bridge experience the designers had.

RE: Miami Pedestrian Bridge, Part VII

Seeing the polish video again and the slow motion dash cam (where would we be without that I wonder), I hadn't fully taken in the fact that the top of no 12 with the top canopy initially falls vertically in the first few frames by quite a long distance whilst the bottom slab only rotates about the edge of the pier.

To me the only way it could do that is if the base of no 11/12 had been pushed out beyond the pier before being pulled back over it as the lower deck got pulled off the pier and the top canopy collapsed down and further into the road.

So sequence was base of 11/12 breaks and moves sideways enough to fall vertically down, top of 11 breaks along with canopy, bottom slab breaks somewhere between 11 and 10 and then starts to fall with base of 11/12 pushed out beyond the pier. It all starts to fold in then as the bottom slab is [pulled off the pier and the top canopy pancakes onto the bottom slab it pulls the top canopy, still attached to no 12 back over the pier to its final resting place.

The speed of collapse and virtually simultaneous fracture is still absolutely frightening.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Miami Pedestrian Bridge, Part VII

Quote (jgKRI (Mechanical) )

Quote (bimr)

Does anyone else think it seems odd that Ms. Figg is not licensed when she is in charge of the bridge engineering business. In fact, many of the players on the project are unlicensed so they don't have to worry about losing their licenses.

Not especially. Lots of companies doing licensed work have CEOs who aren't.

By law, engineering firms are required to be licensed. In Florida, the principal of the firm is required to be a PE. For Figg, that person is probably Mr. Pate. Considering that Ms. Figg (the owner) went to an engineering school, it is unusual that she has never bothered to obtain a PE license.

Based on what happened with the Hyatt Regency disaster, Figg may be at risk of losing the firm's license.

RE: Miami Pedestrian Bridge, Part VII

Quote (bimr)

Considering that Ms. Figg (the owner) went to an engineering school, it is unusual that she has never bothered to obtain a PE license

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

Mr. Pate is titled 'Principal Bridge Engineer' in a few sources mentioning his name via google.

I do agree that Figg Group's licensure is undoubtedly at stake.

RE: Miami Pedestrian Bridge, Part VII

I can see the approach the bimr is taking - the engineering of bridges will require someone to have a PE, but I can see the converse as well; it's my impression, possibly incorrect, that to get a PE one basically has to find a job working under the supervision of a PE for a significant period of time. If the goal is to run a company that would be quite a detour if there was no plan to be an active engineer. I can't say for certain that having a PE would be better in running finance, marketing, engineering, procurement, contracting, legal, and other departments. I can say that one reason I never tried is that the engineering I did was defense work and I think, of the hundreds of engineers I ran into, only one had a PE license, making getting one, for me, an impossibility as I never sought the opportunity to work for a firm where I could work under such supervision.

RE: Miami Pedestrian Bridge, Part VII

Quote (3DDave)

it's my impression, possibly incorrect, that to get a PE one basically has to find a job working under the supervision of a PE for a significant period of time.

This is correct to my knowledge.

In the mechanical or electrical world, finding a PE to work under to properly qualify for the exam is much less likely than in the structural or civil world where the percentage of people with PEs is much higher.

Based on her last name, my suspicion is that Ms. Figg was groomed from early on to take over Figg Group, and she may never have worked as a pure engineer. As the owner's heir she may very well have gone right into the project management side as opposed to pure engineering. If that's the case, than not having a PE license may have never been a hindrance for her.

This quote from bimr is absolutely correct:

Quote (bimr)

In Florida, the principal of the firm is required to be a PE.

BUT the 'principal' does not mean the owner or CEO. It means the Principal Engineer- which at some firms might be the CTO or COE or some other c-suite title, but might also have no fancy title at all.

RE: Miami Pedestrian Bridge, Part VII

Quote (LittleInch)

So sequence was base of 11/12 breaks and moves sideways enough to fall vertically down,

This is impossible, as top of member 11 remains attached to canopy. The length of member 11 can NOT increase, it can only remain the same or decrease. To push out member 12 this far it would have to become separated from 12 first, which is of course quite possible.

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

Quote (jgKRI (Mechanical))

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.

RE: Miami Pedestrian Bridge, Part VII

(OP)
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


Quote (bimr)

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.

Quote (bimr)

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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RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

"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.

RE: Miami Pedestrian Bridge, Part VII

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?

RE: Miami Pedestrian Bridge, Part VII

3

Quote (TheGreenLama)

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

Quote (Cutterhead)

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

Quote (Cutterhead)

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.





RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

Quote (JAE (Structural) )

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.

RE: Miami Pedestrian Bridge, Part VII

(OP)
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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RE: Miami Pedestrian Bridge, Part VII

2
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?

RE: Miami Pedestrian Bridge, Part VII



Quote (JAE (Structural) )

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.





RE: Miami Pedestrian Bridge, Part VII

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).

RE: Miami Pedestrian Bridge, Part VII

Quote (bimr)

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.

RE: Miami Pedestrian Bridge, Part VII

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-ben...

RE: Miami Pedestrian Bridge, Part VII

Quote (jgKRI (Mechanical))

'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.

RE: Miami Pedestrian Bridge, Part VII

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:

Quote (bimr)

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.

RE: Miami Pedestrian Bridge, Part VII

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

Dik

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

Quote (TheGreenLama (Structural))

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

RE: Miami Pedestrian Bridge, Part VII

3

Quote (dik)

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

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


Quote (bimr)

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.

Quote (bimr)

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.

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII



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

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

RE: Miami Pedestrian Bridge, Part VII

Quote (jrs87)

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.

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

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?

RE: Miami Pedestrian Bridge, Part VII

Quote (Alpha Kai (Structural))

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.

RE: Miami Pedestrian Bridge, Part VII

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).

RE: Miami Pedestrian Bridge, Part VII

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).

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII


Quote (quote jrs87 (Mechanical))

Denney Pate - Linda Figg - MCM designs for another project:
http://www.fdotmiamidade.com/userfiles/files/Signa...

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.

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

Quote (bimr)

That is a crime in Florida.

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

Quote (bimr)

(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!

RE: Miami Pedestrian Bridge, Part VII

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.

RE: Miami Pedestrian Bridge, Part VII

Quote (Ingenuity (Structural) )

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

The referenced Miami Signature Bridge Project is a $800 million project, not a living room remodel, where someone seems to be holding herself out as an architect. At best, it is inappropriate. It demonstrates an ignorance of the professional licensing requirements that someone running an engineering business should be familiar with.





RE: Miami Pedestrian Bridge, Part VII

In all of the states (12) I was registered in (retired) the President of an engineering/architect firm had to be registered.

RE: Miami Pedestrian Bridge, Part VII

2
I am wrong about the top of #11 missing more section than the base. What is somewhat interesting is that the remaining north portion of the canopy is longer than the distance from the end of the canopy to the front of the #10/11 blister. The distance from the end of the canopy to the beginning of the blister is 21'-10", while the remaining north section of the canopy is approx. 25 ft.

Watching the Dash Cam video, #10 maintains its top & base geometry in relation to the south portion of the bridge as it falls. This cannot be said of #11. The #10/11 node is positioned south of the center of the #10/11 blister. The canopy breaks directly in front and around the sides of the blister. There is obvious rotation of #11 around the #10/11 node. It is not as easy to gauge the rotation of #11 at its base, in relation to the deck.

There is very little damage to the diaphragm. Even the recess between the PVC pipes is less than a foot deep. In the photo of the NTSB staff examining the PT bar they are all standing atop the rubble strewn deck.

While there is no explanation as to why, it is possible that #11 buckled under the #10/11 node & the very stout & grouted #10/w node & @95% of the bridge mass attached, hammer #11 rupturing the base (allowing both ends to rotate) and sending #12 sliding off the back of the diaphragm. The sliding of #12 accelerates the rotation of the #12/canopy section while the base of #12 traps the bottom of #11, at which point the diaphragm is yanked off the pylon and the lower PT bar is disemboweled from the trapped #11 truss.

The problem I have with this scenario is that it would seem that both PT bar should have extended somewhat beyond the blister.




RE: Miami Pedestrian Bridge, Part VII

Quote (Ronbert)

In all of the states (12) I was registered in (retired) the President of an engineering/architect firm had to be registered.

Had to be registered or were registered? As a matter of course, they may have been registered, but, it may not have been as association requirement that they had to be. JAE notes that it appears that they had to be, but in reality, they only needed signing authority. I think it's a good idea that they are...

Dik

RE: Miami Pedestrian Bridge, Part VII

Quote (epoxybot)

There is very little damage to the diaphragm.

Almost like there was insufficient attachment, perhaps. I would be surprised if buckling happened at a node... perhaps 'crushing'.

Dik

RE: Miami Pedestrian Bridge, Part VII

This is concrete.. can you have buckling without crushing?

RE: Miami Pedestrian Bridge, Part VII

Concrete can have some ductility and you can have 'breakage' and still maintain some strength. The collapse was sudden, and, I would suggest that the failure was the same...

Dik

RE: Miami Pedestrian Bridge, Part VII


dik (Structural)
13 Jun 18 14:06
Concrete can have some ductility and you can have 'breakage' and still maintain some strength. The collapse was sudden, and, I would suggest that the failure was the same...

Dik

In the concrete and masonry seismic survivability world, we did some tests to evaluate your statement. There is some post-fracture life left, but the tail is very short. Grinding and crunching is still absorbing some post-fracture energy, but cannot be relied upon. Embedded ductile reinforcement or ductile material overwraps usually disguise post-fracture energy absorption capability of the masonry or bare concrete.

--CCW1

RE: Miami Pedestrian Bridge, Part VII

Quote (Alpha Kai)

Please, help me with how to reply directly to a comment from a post?

If you want, you can use the "Quote Tool:

Quote (Epoxybot)


RE: Miami Pedestrian Bridge, Part VII

Quote (dik)

Almost like there was insufficient attachment, perhaps.

The deck reinforcing was placed, the truss forms set & #11 rebar cage set, followed by #12. So how does the #11/12 node rebar fit unless it is spliced?

RE: Miami Pedestrian Bridge, Part VII

CCW: I've seen heavily double reinforced sections go through serious rotations and still maintain a substantial part of their strength.

Dik

RE: Miami Pedestrian Bridge, Part VII

This photograph says it all. The bottom of #11 should have been tied into the deck with a massive amount of steel in the form of a load spreader beam, as indicated in red in the image below. Only problem, is that the shear stress at this point was so high that not enough steel could have been provided to satisfy the code requirement. It is quite evident that the person who designed this bridge did not have even a rudimentary grasp of the flow of forces through the structure, nor of how to cater for those forces through the imposition of structural elements.

RE: Miami Pedestrian Bridge, Part VII

5
FIU had grand plans for 'signature' bridge. But the design had a key mistake, experts say...

http://www.miamiherald.com/news/local/community/mi...

Quote:

That resulted in a support piece that was likely not thick enough, and even more significantly, lacked sufficient steel rebar reinforcements at the point where it connected to the deck, all three engineers who reviewed the calculations said. That meant it could not adequately withstand the load of the bridge weight it was meant to carry, nor resist "shearing" stress at the connection to the deck that tended to pull the base of the diagonal strut from its anchor, they said.

RE: Miami Pedestrian Bridge, Part VII

I like that Miami Herald report. Not often these days do I praise the press, but they have done their job in this case. And I have learned a new structural term..."undernourished" to describe an inadequate connection.

Will have to read it more thoroughly later, but think they haven gotten the gist of the problem.

RE: Miami Pedestrian Bridge, Part VII

Quote (Miami Herald)

But the three outside engineers who studied the plan in detail said someone should have caught an error that Beck and Howell characterized as clear.

Quote (Miami Herald)

This is not a big project," Beck said. "It’s a darn pedestrian bridge.

Notwithstanding the other complicating factors such as ABC, the titanium concrete mix, etc., the authors of this article are stating that an engineer's opinion is that the root cause of this failure is an obvious error.

That brings up a question for the engineers that specialize in this design area. Is the error really that clear? Do the engineers quoted in this article have access to additional information?


RE: Miami Pedestrian Bridge, Part VII

But, it did withstand those forces for hours, days, etc. after being set in place on the pylons or piers.

The off-design event that resulted in taking it down was horsing on the two PT rods in #11 to attempt to close cracks that had appeared earlier and was noted in the EoR's prior phone call. The attempt to close cracks by retensioning PT rods in #11 was a committee decision that was an error (In My Opinion). The force vectors from #10 and #11 cross under the blister, form an "X" under the blister and induce a couple into the blister with resulting punching loads off the north and south ends of the blister. The large change in cross-section from relative thin canopy thickness, to the thick blister cross-section causes large stress concentrations at the local junctions from the couple at the change in cross-section. (IMO).

RE: Miami Pedestrian Bridge, Part VII

Quote (Miami Herald)

Beck said the concrete at the point where the bridge failed shattered into unusually small pieces, suggesting it was highly brittle, though he can't say whether that had anything to with the collapse.
I didn't know if this was typical, but noticed the small pieces, as if an "explosion" occurred... also small pieces in the rubble where #9 punched through the canopy. Still wondering why ~5 ft is missing from #11 with rebar/PT rod/duct and PVC pipes still intact.

As discussed here, the engineers for Miami Herald focused on the weak connection.
Had been looking at I-35W connection failure. I wouldn't think there was much design emphasis on the #11/12/deck connection - they should have taken another look at numbers after cracks appeared and seen something was wrong.

Description/computer model of bridge. Animated failure starts at 4:00. Curious if they can do similar with FIU/exploding concrete.
https://www.youtube.com/watch?v=5L6fsel9hwg

Partial report from NTSB - they wanted to see calculations for gusset plates, but couldn't
https://www.youtube.com/watch?v=MIunA2Cs98I
(MH article said engineers reviewed nearly 2000 pages of calculations - wonder if any for the #11/12 connection)

They have a memorial of the failed I/35W gusset plate (kinda cool..). Just a piece - these were 6' by 9'
https://www.youtube.com/watch?v=-u3gXy3Ta5Q

RE: Miami Pedestrian Bridge, Part VII

To answer your question, bimr, the engineers quoted by the Miami Herald did have additional information. The article stated that they had the calculations, which were obtained through a freedom of information request.

RE: Miami Pedestrian Bridge, Part VII

I don't concur with their comment about the irregular shaped web... this feature would have made me go into 'overdrive' because of the irregular nature of it. As they say, "Familiarity breeds..."

Dik

RE: Miami Pedestrian Bridge, Part VII


Quote (hokie66 (Structural) )

To answer your question, bimr, the engineers quoted by the Miami Herald did have additional information. The article stated that they had the calculations, which were obtained through a freedom of information request.

hokie66, you have said from the beginning that it was a problem with the connections. Is that "clear" from just a cursory look at the design drawings?

RE: Miami Pedestrian Bridge, Part VII

I noticed the Miami Herald report entered a caveat:

Quote:

The engineers consulted by the Herald cautioned that the apparent design error may not be the sole cause of the collapse.

RE: Miami Pedestrian Bridge, Part VII

bimr,
Yes, I think the problems with this system, being not a traditional truss, but rather a truss/frame, were obvious to some of us. The bridge was weakest at the end where it failed, but I hope the NTSB focus is not solely on that connection.

I further think that the issues should have been found by the independent peer reviewer, if the review was indeed done. I would like to see the Herald reporters turn their attention to that review.

RE: Miami Pedestrian Bridge, Part VII

(OP)
Please discontinue posting in this thread. Go to Part VIII for any further posts.

This topic is broken into multiple threads due to the long length and many images creating longer load times for some. If you are NEW to this discussion, please read the following threads prior to posting to avoid rehashing old discussions.

Part I
thread815-436595: Miami Pedestrian Bridge, Part I

Part II
thread815-436699: Miami Pedestrian Bridge, Part II

Part III
thread815-436802: Miami Pedestrian Bridge, Part III

Part IV
thread815-436924: Miami Pedestrian Bridge, Part IV

Part V
thread815-437029: Miami Pedestrian Bridge, Part V

Part VI
thread815-438451: Miami Pedestrian Bridge, Part VI

Part VII
thread815-438966: Miami Pedestrian Bridge, Part VII

Part VIII
thread815-440072: Miami Pedestrian Bridge, Part VIII



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