Miami Pedestrian Bridge, Part XIV 78

[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

Part XI
thread815-454998

Part XII
thread815-455746

Part XIII
thread815-457935

 

[epoxybot]

This is not a simple delamination. It is the initiation of a split between the upper & lower PT bars. It is occurring under its own weight, prior to the PT bar detentioning.

At 3:00PM VSL - Kevin Hanson informs SAMUEL NUNEZ, Project Manager Structural Technologies VSL, that they don't have hydraulic oil for the equipment and asks for the grade required.

At 3:09PM SAMUEL NUNEZ, Project Manager Structural Technologies VSL, responds that the grade required is AW32.

 

[Sym P. le]

It is occurring under its own weight, prior to the PT bar detensioning.

That is an excellent and important detail. It points to how deficient the reinforcement was, both by design and installation.

I don't believe this is a sophisticated failure. [bold]The bottom three column hoops were omitted (by the designer)[/bold] and though some of the longitudinal bar was intended to be meshed inside the node rebar, the adequacy of this let alone the execution is hardly a substitute.

The collapse was temporal to the retensioning of the PT rods and thus the activity played a role but this structure was distressed and likely to fail short of immediate intervention, namely shoring.

 

[Sym P. le]

From the NTSB interview of ALEXIS MOLINA Corradino Group Witness Interview Transcript (formerly 628471), it is clear that he photographed damage to Member 11 before the destressing commenced and that the destressing did not seem to cause further damage to those cracks.

This is quite the revelation given that we have been led to believe that destressing was the problem.

Page 15

Page 39

Page 40

 

[Sym P. le]

It's like a double pump shot in basketball only better, a triple pump. Once when the shoring was removed, twice when the span was set down on the pier, three times a charm when the PT rods were retensioned. What could go wrong?

 

[epoxybot]

And this is where you have to go back to Denny Pate's understanding of the timeline of cracking. His lead on the project may have known that the cracking was 'pre-destessing' but I think this was overlooked in presenting Denny Pate with the, then current state, of the cracked north end of the bridge.

That is not to say that re-stressing number 11 made any sense to begin with. It never the less remains that if he didn't understand that the bridge was, in fact, failing under its own weight prior-to destressing; that had he been informed of such, his decision making might have taken a different course of action.

Wasn't his lead on the project on vacation for a week or two, immediately after the bridge was set into position? It also doesn't appear that MCM recognized or made a point to convey a clear timeline of cracking, not realizing it could be significant to Figg's review.

Sym P. le - Congratulations on making it through the Alexis Molena transcript.

 

[SFCharlie]

I'm sorry but, I'm old and have forgotten some of the detail, but didn't the first person that took pictures of the cracks after the support was removed and before the move, ask that his concerns be addressed by, was it the principal engineer, or just the engineering firm?

SF Charlie
Eng-Tips.com Forum Policies

 

[epoxybot]

Yes and they should have performed non-destructive testing (Impulse Echo) to understand the degree of section loss but the structure was in a process of self collapse. How Denny Pate may have understood the condition of the bridge, had he known that the crack photos, were taken by ALEXIS MOLINA, prior to de-stressing of member 11, as opposed to being the result of de-stressing; his thinking might have been different.

Why he couldn't see & understand that the north end of the bridge was blown out is another matter.

 

[Sym P. le]

Please allow me to move the discussion to Miami Pedestrian Bridge, Part XV, Thank-you.