Miami Pedestrian Bridge, Part XI 32

[JAE]

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

Part I
thread815-436595

Part II
thread815-436699

Part III
thread815-436802

Part IV
thread815-436924

Part V
thread815-437029

Part VI
thread815-438451

Part VII
thread815-438966

Part VIII
thread815-440072

Part IX
thread815-451175

Part X
thread815-454618


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[Earth314159]

Has anybody noticed the jbar in the youtube video > FIU Bridge Collapse Lift off of 12 explains J-bar pristine condition < does not match up to the drawing?

I believe the hooks were above the shear plan at the base of #12. The shear plane dips down below the pour joint at #12. The concrete above the shear plane was shattered rather than pulled over. It is very interesting that the bar came through relatively unscathed.

I believe the shear plan dips below the pour joint at this location since there is some heavy vertical reinforcing in #12.

 

[Sym P. le]

Regarding the clean rebar, another thought. My initial thought was that a hammering impulse from an initial crushing of 11 (mid-length) could be the cause but in addition, this would instantly release the tension in the PT rod which could reverberate and clean the adjacent J-bars. I can't imagine how violent that failure was. I don't have experience in this field.

 

[SFCharlie]

Re: Construction Engineering, & EQUILIBRIUM
His web presence has included several channel names. One of his websites was for wedding photography.
He is very enterprising, searching out info on the collapse, including feedback from his subscribers, monitoring this site... He refuses to provides links to his sources. That's how I found this site, search for a link to one of the photos he used in a clip. He has long held that the collapse started somewhere else than 11.12. He holds the participants on this forum in disdain.

SF Charlie
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[MikeW7]

I found an active link for the dash-cam video, in case anyone is interested. It's on the FaceBook page for WSVN-TV in Miami, a Fox affiliate.

It has the same resolution (1280x720) as the one I've been using, but it has a larger file size (5.3MB versus 3.3MB) because it isn't as compressed, hence there is more detail in certain areas. You can see more of the safety netting fence posts, for example. The improvements are small, but may be significant is you are trying to glean information from a small cluster of pixels.

I made an enlarged, cropped video for frames 72-90 using the same procedures as before. The video, and frames, are included in this ZIP file.

 

[RAB678]

So how about this one......
FIU? Bridge photogrammetry 17 by Zac Doyle also on youtube.
On my monitor, I can see the end of the crane, vibrate what looks like twice.
Can anyone back this up? about at 22 seconds in.

This is exactly when the start of fall begins.
You should see vibration and then the magical unexplained mystery bulge at the North end of 12.

If the crane is maybe supporting the tensioning cylinder and the worker.
What makes the crane vibrate twice?
Certainly the weight of 400? lbs would not make it do this?
Also notice a black lifting strap? suddenly shoot upwards out of the picture.
Given the weight of the cable and hook?.......
What would you be doing to load this cable, cause that strap to shoot upwards,
vibrate the crane twice and at the same time the bridge falls?

At the the time they were tensioning 11's rods.
Given the OSHA picture of 11a top? rod was spun in about 2 inches.
Since they claimed they were incrementally tensioning. unknown if incremental or fully before second one.
It would lead one to believe tensioning the lower one dropped it.

Either thru concrete laxation or rebar snapping. or both in reverse order.
Now while 11a (top) rebar appears intact, we could assume......the concrete failed around it at the bottom.
And 11b appears sheared but its bottom still embedded in the deck.

So..........did tensioning make it snap? I would think if the foot moved over the protruding end of 11b rod while intact, then the end would be bent somewhat. But it does appear straight.
The longer portion of the rod itself appears bent near the base end. Which could have happened when 11 slid North, it became trapped and got bent then.

Note: While in the pictures it still appears connected. It could have simply fell back into its previous position. OSHA pictures show some powdered concrete on the bar end.
I wouldn't think they would have cut it right there for examination.
Leading me to believe, it snapped right there.

SO......THE QUESTIONING PART...........
IF you were lifting the canopy to reverse the sagging and close the cracks.
You would be lessening the friction of 11 base area. Meanwhile.... tensioning the bars. NOW the rods would be under apparently MAXIMUM tension. Basically cocking a gun. Then SNAPPED 11b. The force unloaded would decimate the end. The crane becomes more loaded, cable lift device lets go. Crane vibrates. 11 sends the end outward in pieces. Falls down. Simple conclusion really.

Any thoughts on all this?

Sorry I am not a decent writer.
Analyzing mechanical systems and why they failed or how to make them better, I would be better at.

 

[zeusfaber]

Please discontinue posting in this thread. Go to thread815-455746: Miami Pedestrian Bridge, Part XII: Miami Pedestrian Bridge, Part XII 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: Miami Pedestrian Bridge, Part I

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

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

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

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

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

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

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

Part IX
thread815-451175: Miami Pedestrian Bridge, Part IX: Miami Pedestrian Bridge, Part IX

Part X
thread815-454618: Miami Pedestrian Bridge, Part X: Miami Pedestrian Bridge, Part X

Part XI
thread815-454998: Miami Pedestrian Bridge, Part XI: Miami Pedestrian Bridge, Part XI

Part XII
thread815-455746: Miami Pedestrian Bridge, Part XII: Miami Pedestrian Bridge, Part XII