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Miami Bridge Collapse

03/16/2018 8:45 PM

The suspension bridge that collapsed in Miami was apparently erected without a support column or suspension cables. Comments?

https://www.usatoday.com/story/news/2018/03/16/miami-bridge-collapse-suspension-cables-support-tower/431418002/

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#1

Re: Miami bridge collapse

03/16/2018 9:16 PM
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#2
In reply to #1

Re: Miami bridge collapse

03/16/2018 9:31 PM

If you ask me they should have stopped traffic while they were performing the stress test.....which they probably will from now on I'm guessing...

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#13
In reply to #2

Re: Miami bridge collapse

03/18/2018 12:21 AM

I've noticed that the higher you go up the food chain, the greater amount of risks beings take,,and sometimes the results are fatal.

Whereas the lower you go on the food chain, the lesser amount of risks are taken,,with the results always being fatal.

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#35
In reply to #13

Re: Miami bridge collapse

03/18/2018 11:50 PM

I see I got an, " off topic " . The truth is, people have to die, before someone decides to build or engineer things the correct way. How many times have you seen these :

The road curves to the left, but the camber is to the right or to the outside of the curve.

Someone gets the brilliant idea to install cobble stones before the entrance to the roundabout.

A sharp curve is installed at the bottom of a steep hill.

The list is endless.

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#38
In reply to #35

Re: Miami bridge collapse

03/19/2018 6:47 AM

Just as well the Greeks can build bridges that don't fall down in a couple of days!!!!

Just as well it was only a footbridge........they could always rename the area:-

I don't think it would be a misnomer!!!!.........after all they did pull a REALLY BIG ONE

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#93
In reply to #13

Re: Miami bridge collapse

03/26/2018 12:17 PM

Really?

This is everyday risk on the lower rungs of the food chain....

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#23
In reply to #2

Re: Miami bridge collapse

03/18/2018 10:07 AM

Here is an excellent (and at times funny* and profane) analysis of why the collapse occurred. Repeat: at times profane, so if bad language bothers you, don't watch. And yes - he deliberately mis-pronounces words sometimes. It's part of his gimmick.

(*He's not being funny about people getting killed.)

https://m.youtube.com/watch?v=KtiTm2dKLgU

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#26
In reply to #23

Re: Miami bridge collapse

03/18/2018 12:29 PM

Traffic Allowed to Continue after Post-Tension Failure, WOW !

Good video. Malaprops were great, could have done without potty-mouth but it was worth it for content. I did not know about the post-tensioning failure and that was a strong warning to shut down the road. Asymmetry is even more prominent now. The slightly lengthened hypotenuse of the end truss triangle would additionally lift that end of the truss on the small upper cross section of the column. The floor would place less downward force on the lower column. The upper column would fail at the discontinuity and the floor would step off of the ledge, all of which you see in the aftermath. Not clearing the road after finding the post tension failure is inexcusable in my opinion.

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#30
In reply to #23

Re: Miami bridge collapse

03/18/2018 5:23 PM

Dashcam video of the collapse:

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#90
In reply to #30

Re: Miami bridge collapse

03/23/2018 1:30 PM

By the way, I do not see any of the 4 positioning/transporting supports in evidence during the video of the collapse...

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#95
In reply to #90

Re: Miami bridge collapse

03/26/2018 12:27 PM

No, the transporting supports were not kept in place to (catch?) the truss, if/when it failed, but the the individual struts of the truss did not fail in compression during the collapse, as indicated by the fact that the struts are shown (punching/shearing) through the (less-structural?) ''roof'' but not through the post-tensioned, fully structural, (walking) deck of the truss. This points to the distinct possibility that the concrete design/strength of the (roof) was significantly less strong than the concrete/strength design of the (deck), thereby enabling the collapse...

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#96
In reply to #95

Re: Miami bridge collapse

03/26/2018 4:34 PM

Intriguingly enough, FIU has Bachelors, Masters, and PhD programs in Civil Engineering... Maybe they only concern themselves with (engineering theory), and let other schools (dirty) their hands with (engineering practice) as conducted right outside their own windows?...

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#102
In reply to #90

Re: Miami bridge collapse

03/28/2018 2:22 PM

and your point is? the bridge is in position therefore the transporter is no longer needed. if it were still supporting the bridge, the adjustment of the trusses could not be completed. now maybe a good idea would be to suspend traffic thru the area and reduce the load by lowering the positioning/transporting supports incrementally while adjusting the trusses , therefore if there were failure of a single member, catastrophic failure may be adverted and certainly lives would have been spared.

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#103
In reply to #102

Re: Miami bridge collapse

03/28/2018 2:30 PM

a lot of assumptions are being made as to why....

the bridge is in position therefore the transporter is no longer needed.

whether in position or not... I would think that with what has happened, maybe it was needed to get it into position and secured...

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#25
In reply to #2

Re: Miami bridge collapse

03/18/2018 12:14 PM

My response to learning that it was undergoing initial stress testing with traffic flowing underneath it was What the Fk, are you F'ing kidding me.

Basic rule #1 of engineered structure fabrication and installation: NOBODY, but the personnel key to the work being performed, is any where near the structure during high stress periods.

Basic rule #1b of engineered structure fabrication and installation: Only the most knowledged, experienced and qualified personnel can be key personnel during high stress periods.

It seems #1b was broken leading to the breaking of #1.

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#31
In reply to #2

Re: Miami bridge collapse

03/18/2018 6:59 PM

I guess that's why riggers stand under heavy loads that are being lifted by cranes, etc.........NOT.

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#40
In reply to #2

Re: Miami bridge collapse

03/19/2018 9:32 AM

That's the way of it. Nothing gets fixed until after something bad happens. People get this Russian Roulette mentality, "Been doing it this way for the past 50 years, don't see any reason to change anything now."

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#88
In reply to #2

Re: Miami bridge collapse

03/23/2018 12:22 PM

Yes! - and why did the support vehicles have to be removed...?? they could have stayed in place whilst the tests were completed.....!!

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#116
In reply to #88

Re: Miami bridge collapse

03/31/2018 6:45 PM

Probably because the trailers and jacks would cost $600,000 per day.

or because the trailers would spoil the view for the TV cameras booked to promote FIU as the prestigious high tech place to enrol .

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#72
In reply to #1

Re: Miami bridge collapse

03/21/2018 12:31 PM

The excellent Post by SolarEagle contained an excellent link to an excellent feature article that forecast the appearance of the (Pratt Truss) bridge in question...

That article referenced the Standard ''ASCE 7-95 Minimum loads ~ '' as part of the structural basis for the design applied from 1995, onward...

However, the current version is ''ASCE 7-16 ~'' for 2016, onward...

The one applicable during the design alterations may have been ''ASCE 7-10 ~'' for 2010, onward...

There was also a version ''ASCE 7-05 ~''... (one copy of which I have... )

Code alterations are made for specific reasons (probably based on construction mis-haps...) and thus, only the most current Code Standards are to used...

With this bridge, maybe the most current Codes were not all used...

( In any case, I give this post a hearty ''GA'', and I would give the link a ''GL'' if I had that option... )

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#78
In reply to #72

Re: Miami bridge collapse

03/21/2018 4:48 PM

I guess one could call this ridiculous post "number-dropping", which is even less effective than name-dropping. Until you flesh out what earlier provisions the bridge design might have fulfilled, versus which later provisions it might have failed, your post is totally meaningless, as usual.

Cutesy-pie typographical effects (bold, italics, other shouting) only diminish your cause.

Fake Latin quotations, especially misspelling illegitimi, don't help, either.

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#79
In reply to #1

Re: Miami bridge collapse

03/21/2018 8:06 PM

Look closely at the bottom picture in SolarEagle's #1 post above...

The edge of the bottom deck slab of the bridge did not fall parallel to the face of of the bottom of the support, with approx. a 3 to 6 degree wedge of space is clearly visible, and is by itself, evidence of something just not fitting right...

It's almost as if the bottom bridge deck was was pulled off the top support points of the abutment, possibly indicating that the primary failure was at the other end of the bridge...

Now exactly where was that bridge ehibiting one, or more, cracks?...

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#80
In reply to #79

Re: Miami bridge collapse

03/21/2018 10:27 PM

"It's almost as if the bottom bridge deck was was pulled off the top support points of the abutment..."

Do you think that the crane applying the test strain was responsible for that action?

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#81
In reply to #80

Re: Miami bridge collapse

03/22/2018 12:01 PM

It is hydraulic tensioning jacks, directly attached to the post-tensioning cables, that are supposed to apply the increased tension...

If the crane was (also?) pulling anywhere on the bridge, then that is so wrong that I don't see that as what actually happened, but I've been wrong before...

The road-side face of that canal-side abutment is visibly not parallel to the adjacent roadway for unspecified reasons...

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#98
In reply to #1

Re: Miami bridge collapse

03/27/2018 10:09 PM

There are NTSB photos emerging of one Truss where the tensioning cable has blown out of the concrete.

Is it possible the cable was not centered in the truss before the concrete was poured and caused bending loads as it was tightened ?

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#99
In reply to #98

Re: Miami bridge collapse

03/27/2018 10:28 PM

I think that one truss cable may have accounted for the crack (no specification as to location), but unless all truss cables were similarly misplaced, I doubt that it would have been the cause of the failure.

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#100
In reply to #98

Re: Miami bridge collapse

03/28/2018 12:11 PM

That is a distinct possibility, because of the (struts), all being located along the center line of the bridge/truss, and thereby, are primarily resisting compression, rather than tension and/or flexure, over and above the flexure-resisting capacity of standard compression steel column configuration of rectangular strut/column design...

The question is whether most all of the struts were similarly intended to also resist tension and/or flexure?... or just the one shown in the photo?...

The design process of a relatively unique structure, like this bridge/truss, should have included some kind of computer (modeling/FEA/other software), rather than just straightforward analysis software the address such details...

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#104
In reply to #100

Re: Miami bridge collapse

03/28/2018 3:52 PM

The photo in post #98 shows the tension cable-conduit completely outside/below of the rebar cage when cable conduits are conventionally placed completely inside the rebar cage...

It's not supposed to be that (easy) to spall-off the outermost concrete from any structural member...

That is not standard post-tensioned concrete design at all...

The middle photo in post #22 shows where the end of the cable conduit is visible above the bottom of end of the (walking) deck, like it is typically done...

There are undoubtably lateral rebars below the conduit cable...

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#107
In reply to #98

Re: Miami bridge collapse

03/29/2018 8:30 AM

The 'coffee cups' look like a loose fit. This suggests the concrete did not tightly grip the cable and if it did would have given added stiffness to the structure..... whether that matters I don't know.

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#3

Re: Miami bridge collapse

03/16/2018 10:03 PM

extremely efficient failure.

shouldn't be possible.

embarrassing to say the least.

stress testing with traffic moving under?

originally thought the stressed concrete buckled.

wow and terrible

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#4

Re: Miami bridge collapse

03/16/2018 10:22 PM

I'm thinking that if the bridge is designed to be supported by suspension cables, then there should have been some temporary support underneath if the suspension cables and tower were not in place before the bridge was used or traffic was allowed to pass underneath.

But, it would have made more sense to install the tower first, IMHO.

Haste makes waste...

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#5

Re: Miami bridge collapse

03/17/2018 8:58 AM

"engineer reported cracks days before"

No surprise there.

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#44
In reply to #5

Re: Miami bridge collapse

03/19/2018 12:36 PM

Yes, the bridge was starting to fail by that time... ''Red Flags'' should have gone up then...

Some type of structural material was starting to fail, be it soil foundation, concrete (not) curing, connection steel failing, and/or stressing cables not strong enough, as it does not appear from the video that either main support was struck by any moving vehicle, to initiate such a failure...

(asphalt is not a stuctural material, it is a protective surface wear course, only...)

Actually, the expansion-contraction joint(s) could have been designed inadequately, as well...

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#6

Re: Miami bridge collapse

03/17/2018 9:45 AM

I heard on the news that they were tightening the cables at the time of the failure per Marco Rubio.

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#27
In reply to #6

Re: Miami bridge collapse

03/18/2018 1:18 PM

Marco Rubio? Really? Are you suggesting that he HAS A CLUE about anything? Really?

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#39
In reply to #27

Re: Miami bridge collapse

03/19/2018 8:05 AM

I am not suggesting that at all. I am simply stating what I saw on the news.

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#7

Re: Miami bridge collapse

03/17/2018 10:46 AM

They updated the story supplied in your link (bolded parts by me):

"Corrections and clarifications: This story has been corrected to describe the pedestrian bridge as a truss design, despite its cosmetic appearance as a cable-stayed bridge.

The central column and cables that appeared in the design of a collapsed pedestrian bridge in Miami were decorative and not needed to support the span, federal investigators and bridge designers said Friday."

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#12
In reply to #7

Re: Miami bridge collapse

03/17/2018 8:50 PM

Well, it might have failed later under the weight of the decorative supports.

It will be interesting to see whether it was a design problem or a material (construction) problem. In any case, somebody messed up big time.

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#14
In reply to #7

Re: Miami bridge collapse

03/18/2018 12:26 AM

If this is a truss bridge (like the first metal one in this post) then some asymmetric mind has had strange thoughts about how the forces were balanced.

The cable bridge had no chance at all as it lasted only a few days.

Don't they do tests on the ground before? Or a load test as required with all bridges?

Was this 14 Million or half?

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#8

Re: Miami bridge collapse

03/17/2018 11:23 AM

Rant

Can't we simply make a bridge and get over it?

What is the value of simulation software, university, excessive math, usa style over engineering, over confidence and over paying?

Zilch.

Final cost = several lives and tens of millions of dollars

Decorative = from over function

When is enough too much?

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#15
In reply to #8

Re: Miami bridge collapse

03/18/2018 12:26 AM

What I can't understand is, with a perfectly good cross walk and signal lights, why was a bridge needed in the first place ?

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#9

Re: Miami bridge collapse

03/17/2018 12:18 PM

I understand the bridge was constructed on the side of the highway and then moved into place spanning the roadway. I wonder how long the concrete was allowed to age before moving it. I also heard the contractor had another bridge failure, I think in Missouri; might be a case of cutting corners by the contractor to save money/maximize profit???

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#10
In reply to #9

Re: Miami bridge collapse

03/17/2018 4:19 PM

Roadside assembly of trailered in pieces I would guess?

Time will tell.

Where's fredsk with the fact round up when you need him?

Thankse

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#16
In reply to #9

Re: Miami bridge collapse

03/18/2018 12:29 AM

If at first you don't succeed, try,try again.

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#37
In reply to #16

Re: Miami bridge collapse

03/19/2018 6:10 AM

............and if you still do not succeed.........GIVE UP!!!!

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#20
In reply to #9

Re: Miami bridge collapse

03/18/2018 7:20 AM

If the design/construction was focused on saving money, then I guess the inquest will be focused on saving faces.

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#11

Re: Miami Bridge Collapse

03/17/2018 4:51 PM

4-letter accident description: OOPS!

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#17

Re: Miami Bridge Collapse

03/18/2018 1:21 AM

Some CE+PE is probably going to be in trouble unless the construction company did not bother to retain one for the design (which would be illegal and require forgery) and/or didn't follow the construction procedures.

There could also be a political element that contributed.

This was preventable.

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#21
In reply to #17

Re: Miami Bridge Collapse

03/18/2018 7:51 AM

Most of the time, the engineering and design is not at fault but certainly could be and must be investigated. I am totally against a design that would use a fake suspension décor item to be used if that is the case. Suspension bridges have a much better track record than Truss designs and it would have been easy to design a combination Girder/Truss/Suspension design that would have been esthetically pleasing and lower in cost and much safer. Sharing loads and stresses would have been much better in the soil conditions in that area.

Certainly fault lies with either a management or political for allowing the continuation of traffic flow while testing was taking place, although the nature of the failure indicates that a failure would have occurred during later use if it hadn't occured during testing.

From experience investigating failures (not CE type) I would be most concerned with a decision by management to "save money" rather than a technical error.

It is extremely regrettable that human lives were lost and this needs to be fully investigated, I only hope it will be.

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#45
In reply to #21

Re: Miami Bridge Collapse

03/19/2018 12:58 PM

As a point-of-information, a Civil Engineer with a Professional Engineer license should not have had the final authority to ''sign-off'' on such a bridge design... I know the because I am one...

At least one, or more, licensed Structural Engineer(s) (i.e.: an ''SE''), should have had the Final structural ''say-so'' to accept the design responsibility for the structural design of such a bridge...

Additional point-of-information, more strictly speaking, the only cables in that structure were either for ''prestressing'', or ''post-tensioning'', it... There are no cables in it for ''staying'', or ''suspending'' it... Media miss-speak struck again, but they sounded kind of cool at the time...

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#47
In reply to #45

Re: Miami Bridge Collapse

03/19/2018 1:53 PM

However, the Final design was of a cable-stayed bridge, such that the central support to which the cables would have been ''stayed'' is not yet in-place at the left-most side of the view shown by Rixter's #30 live-video post...

Can I give it a ''GV'' award for ''Great Video''?...

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#56
In reply to #47

Re: Miami Bridge Collapse

03/20/2018 12:01 PM

Due to subsequent release of relevant data, I stand re-apprised that the cable-staying design wound up being the pre-final design...

Did no one, at that time, give any warning about ''changing horses in the middle of a stream'' ?...

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#18

Re: Miami Bridge Collapse

03/18/2018 4:38 AM

Three factors requiring investigation .

1) had the bridge been moved before the concrete was fully cured ( one close up photo shows dark grey concrete on a diagonal truss suggesting the possibility it was too green)

2) this type of Center truss design is unlikely to cope well with torsion , if it was twisted during transit due to uneven road surfaces that could have caused the cracks identified days earlier.

3) once it was installed were the ends of the truss supported evenly to prevent torsion ? If the supports were not level at each end then one side of the beam would take all of the load at that end

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#19

Re: Miami Bridge Collapse

03/18/2018 7:01 AM

It was not an accident...Just inadequate engineering.

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#22

Re: Miami Bridge Collapse

03/18/2018 9:28 AM

Symmetry is Your Friend. Corollary: Asymmetry is ?

So, to tune SolarEagle's comment that it is a truss design, I assert that it is more precisely a half-truss design. The right hand side of the truss is absent with the huge bunches of steel normally crossing the column terminated right on top of the column with only the center part of the column which extends to the roof reinforced into the column with a relatively whimpy amount of reinforcement. If you look at the aftermath picture you see little or no damage to the edge of the lower part of the column where the floor of the walkway apparently stepped off of the column. Had the other half of the truss been in place with the steel crossing the lower part of the column there would have been no way for the floor to step off. Those huge bunches of reinforcement would have provided a lot of support to the floor.

So, while post tensioning if you flex the structure enough to drag the floor off of the column edge, down she goes. Look at the triangle at the truss midpoint(which due to the asymmetric design is now the endpoint.) Its bottom point snapped the column right at the discontinuity and the triangle rotated the roof segment to the ground. Regardless of whether anything else failed, the lack of symmetry at this point can be blamed for the structure dropping all the way to the ground. Those big bunches of steel in the floor need something to pull against when you eliminate the other half of the truss or the floor of the truss simply steps off of the bottom half of the column.

thewildotter

I claim no professional expertise, but that is how I perceive this failure.

The Half Truss(blue in place, gray missing, floor reinforcement truncated)

The Prematurely Terminated Big Bundles of Reinforcement(The guy is looking at them and at the nearly bare opening between the floor and the lower part of the column.)

And the Whimpy Vertical Reinforcement at the Center Only.

And the Truss Triangle which Snapped off the top half of the Column and fractured the roof when its roof point rotated to the ground.

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#24
In reply to #22

Re: Miami Bridge Collapse

03/18/2018 11:17 AM

Details

To be totally explicit, I am not contending with the original post analysis beyond saying that asymmetry played a significant role. Just noting that with a full truss the tension on the floor cables would have had symmetric loading from the two halves of the truss. And a full truss would have had massive steel crossing the lower column segment which would have been a significant safety factor to avoiding such complete collapse. I muse that shifting the flex of the structure from approximately uniform to the virtual truss center at the truncated end likely snapped the column, ruptured the anchor, stepped the floor off of the column ledge and overwhelmed that little crane so it is likely that many things were happening simultaneously. All this is why at many construction sites whenever stress testing or post-stressing the dangerous areas are cleared of personnel which has been amply suggested elsewhere.

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#59
In reply to #24

Re: Miami Bridge Collapse

03/20/2018 3:12 PM

Rixter DashCam Video Confirmation of Actual Sequence of Events

At the end of the seventh second of the DashCam referenced video one can see the overall structure go from end-to-end convex upward to convex downward at the left end quite abruptly. That means that the left end accelerated downward just about where the crane boom crosses the structure as the tenuous flex symmetry abruptly shifted. Once this huge mass was moving everything resisting that movement easily failed thus fracturing the roof and the vertical midpoint(at the cross-section discontinuity) of the vertical column. The left end continues rapidly to the ground even faster(truss spring stored energy + gravity) than the object(unfortunate worker?) at the crane cable. The asymmetry of the half truss(note the angle variation on the diagonals) transferred the downward force toward the ground more smoothly on the right than on the left, setting up the chance for the flex curve shift. The failure of the specific post-tensioning bolt through the hypotenuse of the leftmost truss triangle was foreshadowing and contributing to the overall failure. The floor reinforcement had nothing to hold on to, flexed upward, and stepped off of the column ledge.

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Truss Curved Smoothly Upward

Truss Curving Down Slightly on the Left

Left End of Truss Accelerating Downward,

Column Snapping, Roof Fracturing, Floor flexing, Worker Nearly Airborne

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#48
In reply to #22

Re: Miami Bridge Collapse

03/19/2018 10:18 PM

Good Answer! Great illustration! Clear pix! Good text! GA from me.

By the way, the diagonal wire braces are for transportation stability, and not for primary structural stability, like the main overhead stays not yet in-place, because they have to come off in order to give pedestrians convenient access to cross the bridge, after it is fully completed...

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#28

Re: Miami Bridge Collapse

03/18/2018 1:44 PM

This is a question totally separate from "why did it break." If this was a truss design, and the cable stays and tower were just cosmetic--why? Why would someone spend that kind of money for something that is cosmetic? Maybe to help support future load??? Maybe to increase the safety factor???

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#29
In reply to #28

Re: Miami Bridge Collapse

03/18/2018 2:51 PM

They didn't spend the money, because, OMG, they told the architect no. Now the bigger question is why was an architect involve in the design of the bridge?

Something is not copacetic about all this. Using our good friend Oxam and his Razor a very good case can be made that the original design was a cable stayed suspension with secondary trusses for aesthetics, somebody got the (not so) bright idea to invert the design to truss work (availing it to pre-assembly then one-piece installation) with aesthetic cables, and then the cables were ditched altogether.

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#55
In reply to #29

Re: Miami Bridge Collapse

03/20/2018 11:40 AM

Maybe it was an academic decision based on the theory that the aesthetics would be enough for the bridge to ''hold up?''

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#57
In reply to #55

Re: Miami Bridge Collapse

03/20/2018 1:03 PM

I know you are being facetious, but

FYI: I am the Technical Partner in a firm that exclusively designs, builds and installs steel sculpture which ranges form table top to 25-Ton in size. Be clear - be very clear, in the world of big steel sculptors one universally held thought is that anybody who thinks "that aesthetics are enough for structural integrity" is a fool.

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#60
In reply to #57

Re: Miami Bridge Collapse

03/20/2018 4:11 PM

Actually, I was trying to be sarcastic...

That aside, in all seriousness, it is clear that the subject project suffered from serial mis-management...

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#61
In reply to #60

Re: Miami Bridge Collapse

03/20/2018 5:33 PM

Agreed, and I disagree with the off-topic rating you got. It is my belief that the trigger cause was the cable tensioning, the proximal cause was the offsite fabrication and then damage during transportation for installation, and the root cause can be found somewhere in the design process to choose this type of bridge and installation. I am haunted by the ghost cable stayed tower and cables. Why would anyone design in an aesthetic enhancement on a tertiary, if not quaternary, infrastructure improvement if that enhancement was going to add a good 20% tax, title and license cost to the project? One of the primary drivers to infrastructure design, fabrication and installation companies and their clients is cost containment. A 20% added cost is absolutely counter-intuitive to this primary driver. The ghost just does not make sense.

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#62
In reply to #61

Re: Miami Bridge Collapse

03/20/2018 6:32 PM

Agreed.

I did not catch any (news bite) about how the design was changed to omit the tower and cables, until being able to read #22... I was simplistically thinking that they would be added later (silly me...)

Years ago, I handed a folder of project papers to a very experienced and respected Director of Public Works. It had a fair amount of paper in it, so I had folded the folder along one of premade folding lines, so the bottom of the folder would sit flat on it's edge in the file cabinet. He then ''jumped down my throat'' about doing so, and told me not to do it again... At the time, I was just speechless, and refrained from asking him why else would the lines be there, and kept my job...

How he became, and stayed, a Public Works Director, without realizing that was what the folding lines were on the folder for, is still beyond me... but sometimes, that's the kind of mind that rises to that level of decision making... This job must have had several decision makers like that...

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#64
In reply to #61

Re: Miami Bridge Collapse

03/20/2018 8:47 PM

I commented on this cost increase quite a bit earlier, but not in such detail. Also mentioned a couple of "maybe" reasons for the cable stayed addition.

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#58
In reply to #29

Re: Miami Bridge Collapse

03/20/2018 2:20 PM
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#71
In reply to #29

Re: Miami Bridge Collapse

03/21/2018 12:06 PM

Stephen, what you saw, in the off-topic vote, is some of the (dark side ?) of CR4 that ''Admin'' empowers by allowing such annonymous (ghost-posting?) of other peoples posts...

I think that CR4 cheapens itself by continuing to allow such (cheap-shoting ?) from unidentified sources... What do you think ?...

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#76
In reply to #71

Re: Miami Bridge Collapse

03/21/2018 2:00 PM

I think off-topic needs some rules about what is off topic: If you "off topic" a post and you are not the originator of the post you should have to gateway by answering yes/no question set of no more than 5 questions (hey this method works for the IRS) to justify your action.

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#77
In reply to #76

Re: Miami Bridge Collapse

03/21/2018 4:19 PM

In a court of law, it is a guaranteed fundamental right to face your accuser, not his/her/their family/friend/ employer/etc., but your accuser, face-to-face...

Is there, effectively, some kind of (Inquistion) allowed in CR4, where the off-topic posters are, in effect, hooded for their own protection, without similar protection for the postees?...

...or, does such infantile behavior pass for professionalism these days?...

...If so, then why in CR4?...

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#92
In reply to #77

Re: Miami Bridge Collapse

03/23/2018 10:10 PM

Nemo censetur ignorare legum. . Rather a consideration is allowed. Similar to the 3 strikes in baseball.

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#32

Re: Miami Bridge Collapse

03/18/2018 10:43 PM

Time to stop worrying about how something LOOKS, and concentrate on how well it WORKS!

Probably save a ton of money!

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#33

Re: Miami Bridge Collapse

03/18/2018 11:01 PM

After viewing our Canadian Friend's video, he pointed out that one of the support carriers on the failure end of the bridge was NOT under a vertical post as shown in the drawing, nor was there evidence of a spreader bar assembly as described on the print between the two carriers. If the picture shown was accurate, a tension load was being applied to the lower walkway by the out of position support carrier.

I just hope that the failure analysis guys and girls can figure this out for all of us.

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#34
In reply to #33

Re: Miami Bridge Collapse

03/18/2018 11:06 PM

Yes, it would be nice if GR4 gives us updates on findings.

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#36

Re: Miami Bridge Collapse

03/19/2018 5:19 AM

The whole point of any test is to establish which side of a pass/fail boundary something lies, under controlled conditions. It seems that the consequences of failure were not addressed in the Risk Assessment/Method Statement for the test.

The principal failure is therefore a procedural one.

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#46
In reply to #36

Re: Miami Bridge Collapse

03/19/2018 1:39 PM

Before the crack nobody would have suspected it could brrak apart like peanut brittle.

After the crack was discovered the writing was on the wall. (To the layperson)

Challenger remembered

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#41

Re: Miami Bridge Collapse

03/19/2018 10:59 AM

this guy found the "smoking gun"

https://www.youtube.com/watch?v=KtiTm2dKLgU

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#42
In reply to #41

Re: Miami Bridge Collapse

03/19/2018 11:05 AM

they didnt have the moving vehicle in the area where the bridge was designed to be moved. the trusses were preloaded for that vehicle and when the mover was placed in a different location they either forgot that the trusses were preloaded or they did not compensate by reducing the load on the end trusses. this youtube video shows the metal bolted out of the truss which had to happen just before catastrophic failure as otherwise it would have been bent in the concrete. in fact, the hydraulic loading device is still connected to that compression rod.

https://www.youtube.com/watch?v=KtiTm2dKLgU

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#84
In reply to #42

Re: Miami Bridge Collapse

03/23/2018 7:58 AM

Yes x 2

after viewing the pretensioning bolt and hydraulic ram which speared out of the truss I guess one more factor to investigate is , was the bolt correctly fastened to the structural node embedded into the floor slab which it is supposed to tie to the truss and the roof slab ?

considering it failed , it was either overloaded or the fastening point was not up to design spec.

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#86
In reply to #84

Re: Miami Bridge Collapse

03/23/2018 11:14 AM

there is some phone message that spoke of cracking or cracking sounds.. my guess is that since the supports were not in the correct location when moving, the area that the bolt jettisoned out was unsupported and overhanging. So the concrete that the bolt was to stress may have been compromised OR the bolt itself which was already pre-loaded saw a lot of force due to the overhang which may have went into the plastic deformation curve and then ultimately failed when the worker tried to bring it back up to the stress level it needed to be at.

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#43
In reply to #41

Re: Miami Bridge Collapse

03/19/2018 12:09 PM

I tried watching the vid, BUT the guy is such a maxed out condescending a-hole tool that after about a minute I wanted to get in my truck, drive here to there to wherever he calls home and kick his teeth in. Instead to keep my kharma somewhat clean I switch off.

Seriously yu'al, if you can't show a little respect for your audience STFU, because whatever you present right, wrong or somewhere between isn't worth being insulted for.

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#52
In reply to #43

Re: Miami Bridge Collapse

03/20/2018 10:24 AM

you were offended? with all the harsh words that come from your mouth, one would expect a thicker skin.

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#53
In reply to #52

Re: Miami Bridge Collapse

03/20/2018 10:36 AM

I have a very thick skin and can be harsh in word, BUT when anybody insults my intelligence and hard learned knowledge as part of their self-aggrandizing schtick I respond very poorly. Mea culpa, mea culpa, mea maxa culpa,

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#49

Re: Miami Bridge Collapse

03/19/2018 11:20 PM

Why not conduct the "stress testing" (whatever that was supposed to be) while the structure was still on the ground?

And what's the nonsense about "cosmetic" stayed-cable appearance, when real stayed-cable construction would probably have been better?

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#50
In reply to #49

Re: Miami Bridge Collapse

03/20/2018 10:16 AM

The media got it wrong; it wasn't a stress test, they were applying the final load on the trusses. This needs to be done once the structure is in its final resting place.

The issue is that they should have stopped traffic at the time.

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#51
In reply to #50

Re: Miami Bridge Collapse

03/20/2018 10:18 AM

Absolutely; see my response #25 to SolarEagle's posting #2.

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#54
In reply to #50

Re: Miami Bridge Collapse

03/20/2018 10:56 AM

That's why I put "stress testing" in quotes. The stresses would naturally need to be adjusted for the difference between end-supporting versus the transporter support points. It will be interesting to see if/when a comprehensive explanation is furnished. (The Canadian enginurring vidayo doesn't quite do the job.)

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#141
In reply to #54

Re: Miami Bridge Collapse

04/23/2018 5:21 PM

The newly revealed plans, state on page 63, sheet B-38
NOTES.
...
8. P.T. BARS IN MEMBERS 2 & 11 WILL NOT BE GROUTED AND WILL BE DESTRESSED AFTER MAIN SPAN CONSTRUCTION IS COMPLETE. DO NOT REMOVE BARS.

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#142
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Re: Miami Bridge Collapse

04/23/2018 6:36 PM

Thanks. This whole project is an interesting (if a bit weird) interplay of aesthetic ideas versus structural principles.

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#63

Re: Miami Bridge Collapse

03/20/2018 8:34 PM

It now comes out that the Florida Department of Transportation imposed a design change on the bridge to move the central pedestal 11 feet closer to the canal, in order to allow for another traffic lane on that side of the roadway. There alreadfy was room on the other side of the bridge for another lane, and lane symmetry should have been provided for, much earlier in the basic design process, and not delayed until the (eleventh hour) of the construction process...

The Bridge was already 2.6 M$ over the 9.2 M$ original construction cost estimate, and behind schedule...

The Corps of Engineers was holding up the permitting process to build the canal-side abutment, for lack of funds to review the revision (?!...), and may have given an unjustified OK in haste...

Alterations were then designed to the tune of 6 M$ more for (hurried ?) design revisions...

Photographs of the pre-collapse cracks were not shown, but increasing the span by 11 more feet to a 109 foot truss probably put too much additional tension on the in-slab cables, causing them to stretch too much, causing the concrete to crack and spread, and allowing the truss to collapse under its own weight...

Once again, haste made waste...

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#68
In reply to #63

Re: Miami Bridge Collapse

03/21/2018 7:40 AM

yea, pretty much what the vidayo said.

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#70
In reply to #63

Re: Miami Bridge Collapse

03/21/2018 11:46 AM

Speaking of hurrying, regarding the 11' extension expnses, I must correct myself thusly;

- design revisions: _____''$204,540''

- construction additions:_''$402,723''

- total cost additions:____''$607,263''

'=> > 600 k$ => $0.6 m$, not 6.0 M$

I sincerely apologize.

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#73
In reply to #63

Re: Miami Bridge Collapse

03/21/2018 1:34 PM

I reiterate my proposition that root cause for this "cluster" lies in the initial design process. It is my belief that the ghost cable stayed system was NOT a discarded aesthetic enhancement, but the original proposed design. Everything else starting with the final choice of the tensioned truss design to, and including, the 17 dead people were just part of a glacial paced cascade failure.

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#74
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Re: Miami Bridge Collapse

03/21/2018 1:46 PM

What 17 dead people? Are you confusing this with a recent school shooting?

That said, I agree with the suspicion about the "cosmetic" cable stays.

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#75
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Re: Miami Bridge Collapse

03/21/2018 1:51 PM

My bad and stand correct with a published 6.

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#87
In reply to #74

Re: Miami Bridge Collapse

03/23/2018 11:54 AM

In a previous posting I suggested that the proximal cause of the failure might lay in the fabrication off site and then transportation. After a bit of "Google Map & Satellite Image" search of the bridge's location I am absolutely convinced so. There is no place immediately or near adjacent to the installation site to fabricate a structure of that size. Which means two things: first, it was a "bit of a hike" from fab site to install site and second, due to the exigencies of transport it required a 90 degree turn for positioning at the install site. In my business we regularly fab offsite, transport and then install. The two things my colleagues I and loose the most sleep over are stress related structural damages occurring during transportation and the unloading/ positioning just prior to the lift/install.

FYI for those who haven't done this process: A simple 6" curb can bring all assorts of "hell to pay" so just imagine having to transport a structure this size for any distance more than a 1/4 mile.

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#89
In reply to #87

Re: Miami Bridge Collapse

03/23/2018 12:49 PM

I just reviewed SolarEagle's posted pictures of the transport/ install vehicles; two separate unlinked transporters is an excellent way to provide an opportunity for stress damage during transportation. Yeah, I know they probably had a skilled operator(s) and IT controls, but whenever I look at big structures on tractor transporters (regular feature on the "Mega Machines" and "Impossible Engineering cable TV shows) I invariably see I a single transporter. Good reason too, the multi-variant 3-dimensional stress field is applied over a single base structure. With two base structures you have a nightmare of stress induced load balancing (can you say flex & torque).

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#91
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Re: Miami Bridge Collapse

03/23/2018 1:43 PM

Can you favor us with a little more jargon about "the multi-variant 3-dimensional stress field"?

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#97
In reply to #89

Re: Miami Bridge Collapse

03/26/2018 6:06 PM

The trailers were linked but the important detail is “ did they have hydraulic controls to allow automatic self levelling of the load during transport”

one end of the load could be fixed but the other would need to automatically adjust and maintain a level state independently of changes in the road surface , this could be done with digital sensors linked to the hydraulic controls.

Some idiot guy mentioned in post #18 above that this type of Center truss won’t cope well with torsion , especially when the concrete is green.

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#65

Re: Miami Bridge Collapse

03/20/2018 9:35 PM

If my recollection is correct, concrete requires a full 28 days to properly "dry" and cure. In addition, proper curing requires that the concrete be kept wet or at least moist for that 28 day period.

The news reports (possibly inaccurate) indicated that the span was "completed off-site" in 8 days.

In view of these factors, and considering that a crack was observed in the structure, is it possible that the concrete was NOT cured, or improperly cured? Could the warm Florida sun have have dried out the concrete without allowing it to properly cure?

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