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Old 17th March 2018, 02:40 PM   #121
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Originally Posted by Bob001 View Post
Basic question (and I apologize if I missed the answer earlier): If this bridge was supposed to be supported by cables extending from a central tower, as drawings indicate, how/why could they remove the temporary supports under it before the tower and cables were constructed? The bridge wasn't designed to support itself.


The bridge segment which was set in place was designed to support itself. While it was only supporting itself, and the rest of the construction continued.

What it wasn't designed to do was support itself and the ultimate, final expected design live load of all the people they anticipated might be using that walkway at once, which was intended to be a gathering and meeting space as well as just a way to get to the other side.

When that bridge got filled with a crowd of people it would need a whole lot more support. Hence the cable design.

Imagine a music concert there with a band or three and lots of people dancing.

There's a reason that the Army has very specific instructions for the way to move troops on foot across a bridge. And marching in step is one of the no-no's

Crowds of people are among the heaviest live loads you can put on a structure not intended for large machinery. Engineers are very wary of them, and tend to over-design for them. I don't blame them even a little bit. Crowds of people are also where you really don't want an engineering failure. The bad press is murder.
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Old 17th March 2018, 03:40 PM   #122
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Here's a link to a .pdf of the original proposal for the bridge.

A couple of points which are germane to the discussion here are addressed early on.

The project was a design-build proposal from a team which was comprised of the construction firm MCM amd the bridge design/construction firm FIGG. FIGG has a long and well-respected reputation for large, complex bridge projects. They would have been intimately involved with all phases of this project.

The off-site construction, transport, and stand-alone installation of the bridge segment was always part of the original proposal. In fact, it was one of the sales points of the proposal, emphasized early and often. This means that the segment of bridge which failed was always intended to be moved into place and to support itself during the subsequent construction.

Use of the bridge as a gathering, meeting, social space was also among the selling points of the original proposal, and the cable stay design was even explicitly called out as a solution for the expected pedestrian load. This also helps explain why they were not particularly concerned about it not being in place during the entire duration of construction. It was always intended as supplemental support for the anticipated potential live load.
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Old 17th March 2018, 03:47 PM   #123
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Originally Posted by Trebuchet View Post
Another note from the second AvE video: He points out that the jack thingummies used to support and move the bridge weren't located as shown on the original drawing, especially at the end that failed. One that should have been under the end of the bridge was instead near the center, because the ground where it should have been wasn't suitable. That left the overhanging end of the bridge unsupported during the move. It wasn't designed for loads in that direction. I'm therefore wondering if that load caused the stretching of the post-tension member which led to its failure when being tightened.

I think he is definitely on the right track. (No pun intended.) Exactly where and how the failure process was initiated may remain to be seen. I'll be interested to hear more about investigation into the loud snapping noise it has been mentioned was heard some hours before the final failure. It may be that other tendons had already failed before the one they were stressing at the time of the collapse gave way.
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Old 17th March 2018, 04:35 PM   #124
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Originally Posted by quadraginta View Post
The bridge segment which was set in place was designed to support itself. While it was only supporting itself, and the rest of the construction continued.
Well, in light of recent events, I question whether that's true.

Originally Posted by quadraginta View Post
it wasn't designed to do was support itself and the ultimate, final expected design live load of all the people they anticipated might be using that walkway at once, which was intended to be a gathering and meeting space as well as just a way to get to the other side.
.....
500 people averaging 150 pounds each would weigh around 38 tons. That's a lot, but the concrete structure itself reportedly weighed 950 tons. Was it really designed to hold up its own weight, and the cables were just for the people?
http://abcnews.go.com/US/fiu-bridge-...ry?id=53775940
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Old 17th March 2018, 04:53 PM   #125
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Originally Posted by FenerFan View Post
Originally Posted by quadraginta View Post
<snip>

There's a lot I could say about the what should have been seen as that rod was being tensioned, but suffice it to say that the workers operating the ram should have realized from the behavior of the pressure gauge that something was wrong.

<snip>
Would this “something was wrong” have occurred slowly as the rod was being tensioned or quickly as a certain level was reached? Also, what would the solution be? I’m guessing that stopping the process would have prevented collapse.

When a post-tension tendon is being stressed to design load (And I'm using the initial pull as an example. Things become weird when de-tensioning and re-tensioning are involved), there is a design load for each tendon measured in Kips ("a US customary unit of force. It equals 1000 pounds-force, used primarily by American architects and engineers to measure engineering loads." Shut. Up., all you Eurocentric metric snobs, now is not the time. ). The workers doing the stressing of the tendons use a hydraulic ram powered by an electric hydraulic pump. This pump has a gauge on it which measures PSI ( or whatever ) of the hydraulic system, and there are charts which are used to translate that number into the amount of Kips which are being exerted on the tendon. That number varies as a result of several different factors.

When the tendon is being stressed two things happen. The pressure on the gauge goes up, and the tendon elongates (i.e. "stretches"). The tendon is pulled until the pressure gauge on the pump unit reaches the design specified value. The elongation is monitored during this process. And then the final elongation is measured and checked to see that it conforms to the amount of elongation which is expected.

If the pressure reading on the gauge has not reached the design pressure and the elongation continues beyond the design elongation for any significant period then there is a problem. What that says is that the tendon's elasticity has reached the failure point where it is no longer resisting the pressure from the ram. Not good.

If you watched that video, that was the point where the curve flattened out. That's what happens right before it snaps

And yes, they probably should have stopped, if, that is, the instruments they had available enabled them to see that it was happening.

Now mind you, since this was a rebar tendon, and a very short one at that, the elongation required may not have been very much, and differences from design might have been very difficult to detect. I'm not blaming the workers. Not yet, anyway.

Also, it isn't very clear to me just exactly why they were messing with it in the first place, since it had been stressed, presumably to design load, already. Having the primary load and elongation values may have had little relationship to whatever it was they thought they were trying to do.

I'm fairly confident that whatever it was was under the direction of the engineering team responsible for the PT design. A lot was going on. Hindsight is always 20/20 and a lot of clues are surfacing now, but they may not have been as easy to put together while it was happening. (And I'm talking about the several days which passed from the time the bridge segment was set down to the time it failed.)
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Old 17th March 2018, 05:40 PM   #126
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Since they appear to have been wondering what was going on it would have been prudent to close the road.

The design was probably good. Something had gone wrong with the implementation since cracking was observed days before the failure.
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Old 17th March 2018, 06:07 PM   #127
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Publicity picture of the bridge with construction info.



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Old 17th March 2018, 06:19 PM   #128
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Originally Posted by quadraginta View Post
The bridge segment which was set in place was designed to support itself. While it was only supporting itself, and the rest of the construction continued.

What it wasn't designed to do was support itself and the ultimate, final expected design live load of all the people they anticipated might be using that walkway at once, which was intended to be a gathering and meeting space as well as just a way to get to the other side.

When that bridge got filled with a crowd of people it would need a whole lot more support. Hence the cable design.

Imagine a music concert there with a band or three and lots of people dancing.

There's a reason that the Army has very specific instructions for the way to move troops on foot across a bridge. And marching in step is one of the no-no's

Crowds of people are among the heaviest live loads you can put on a structure not intended for large machinery. Engineers are very wary of them, and tend to over-design for them. I don't blame them even a little bit. Crowds of people are also where you really don't want an engineering failure. The bad press is murder.
Mythbusters did a demo of that as part of one episode....
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Old 17th March 2018, 06:52 PM   #129
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Originally Posted by Captain_Swoop View Post
Publicity picture of the bridge with construction info.

<snip>

That's taken from the proposal .pdf I linked to a few posts above.

There's some interesting stuff in there for anyone who likes to look at drawings.

Pg. 115 has the details and layout of the truss members. If I'm looking at it right the one they were fiddling with when it collapsed was Truss #11, which doesn't have the number of bar tendons detailed in the schedule, but I think was probably two, with only one of them having the live (stressing) end at the top. The other dead-ends below the anchor blister and pulls from the bottom.

If the 'whip snapping' sound which someone said they heard earlier was the other bar tendon in that truss failing, then when that one failed there would be no primary reinforcing left at all in that truss member.

Whoopsie.

Also interesting, if not particularly relevant to the collapse, the "cable stays" that were going to be attached to the pylon were going to be 16" dia. steel pipes.
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Old 17th March 2018, 07:08 PM   #130
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There was a meeting of the project management about the cracking hours before the collapse.
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Old 17th March 2018, 07:13 PM   #131
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Originally Posted by Captain_Swoop View Post
Publicity picture of the bridge with construction info.



http://i821.photobucket.com/albums/z...psfwlgad6l.jpg
It's a shame homeless people and frat boys won't get the opportunity to pee all on it.
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Old 17th March 2018, 08:19 PM   #132
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Originally Posted by quadraginta View Post
When a post-tension tendon is being stressed to design load (And I'm using the initial pull as an example. Things become weird when de-tensioning and re-tensioning are involved),
<snip>

Also, it isn't very clear to me just exactly why they were messing with it in the first place, since it had been stressed, presumably to design load, already. Having the primary load and elongation values may have had little relationship to whatever it was they thought they were trying to do.
It was mentioned in the AvE video that one of the self-propelled modular transporters (SPMTs) stood at another place than in the drawings the video. I also got the impression from that video that the SPMTs actually supported the bridge segment. Could it be that, due to the different placement of one SPMT, the tension on the PT tendons had to be adjusted to that new situation, and then re-stressed when all was in place?

Or is that a red herring and did the SPMTs do nothing for support, and should the bridge segment have been stable on simply the two piers?
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Old 17th March 2018, 10:42 PM   #133
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Originally Posted by ddt View Post
It was mentioned in the AvE video that one of the self-propelled modular transporters (SPMTs) stood at another place than in the drawings the video. I also got the impression from that video that the SPMTs actually supported the bridge segment. Could it be that, due to the different placement of one SPMT, the tension on the PT tendons had to be adjusted to that new situation, and then re-stressed when all was in place?

Or is that a red herring and did the SPMTs do nothing for support, and should the bridge segment have been stable on simply the two piers?

It isn't clear that the placement of the transport system was a culprit. "Maybe." is still the most authoritative answer.

I've read through and been following the discussion thread on the engineering board I mentioned up-thread. (It's called Eng-Tips Engineering Forums.) There's some good conjecture there. Yes, it is still conjecture, but some of it is informed conjecture, and thought-provoking.

It helps to look at the truss details page (pg. 115 of the proposal .pdf) to follow what they are talking about.

In short (if that's possible) their prevailing theory is that the rod tendons in the endmost truss members (#1 and #11. #11 is the one at the end which failed) were actually only there to provide support for the move itself, and needed to be de-tensioned after the move. This is based on the fact that in the schedule for the truss members on pg. 115 of the proposal .pdf there are no specifications for any rod tendons for those two truss members as part of the structure. The idea being that these truss members were designed to be in compression, and therefore no tension reinforcing was required.

This is where the conjecture starts getting thick. The question is, what exactly were they trying to do with the PT rod they were working on? By all appearances it was one (possibly of two, with the other having its live end at the bottom of the truss segment) which was in truss member #11.

It is possible that this was part of the de-tensioning for after the move, when PT rods were no longer required or even recommended in that truss member, and that when they were trying to loosen the nut on the PT rod they over-tensioned it. (You have to pull 'em a little bit to get them loose, that's always the most hateful part about de-tensioning any PT, whether it is rebar or cable.)

It does seem likely, looked at some of the photographic enhancements in the thread, that truss member #11 buckled and failed, for whatever reason.

It is possibly related to the cracks which were seen. Maybe they decided that re-tensioning that PT rod would help with the cracks that were seen.

It is entirely possible that some damage was done as a result of the changed placement of the transports, and that is what started the cascade of issues which resulted in the collapse.

There's still more to be learned about the whole thing, but I am afraid we are approaching the point where such information isn't going to be as easily accessible as what we have learned so far.
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Old 18th March 2018, 12:29 AM   #134
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Originally Posted by FenerFan View Post
Would this “something was wrong” have occurred slowly as the rod was being tensioned or quickly as a certain level was reached? Also, what would the solution be? I’m guessing that stopping the process would have prevented collapse.
A couple of people are using this term. In post-tensioned structures, these aren't rods, but steel cables (set inside light plastic tubes).
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Old 18th March 2018, 05:19 AM   #135
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Originally Posted by MikeG View Post
A couple of people are using this term. In post-tensioned structures, these aren't rods, but steel cables (set inside light plastic tubes).
You are mistaken. Both in general and in this particular case.

There are different types of PT reinforcing. This includes PT rods, like rebar only with threads instead of deformations, and stranded cable. I have installed both kinds.

Both systems are being used in this bridge structure.


(Although in the case of the PT cables a slightly different (but not uncommon) approach is being used. Instead of the cable tendons each being individually in a greased plastic sheath, which is referred to as an "unbonded" application, multiple bare cables are installed in a conduit, and after being tensioned subsequent to the concrete being poured and cured, the conduit is pumped full of a non-shrink grout to fill any voids. This is called a "bonded" application. It is actually more like the way the typical PT rebar systems are installed.)


The bridge slab and canopy are reinforced with PT cable, although in conduit in a bonded system, and not as individual, unbonded tendons.

The bridge trusses are reinforced with PT rods.

This is clearly indicated in the proposal .pdf which I have linked to a couple of times up-thread, which explicitly call for PT cables in the slabs, and PT "rods" in the truss members..

It is also clear that the truss members are reinforced with PT rods in the photos linked to up-thread which show a hydraulic ram hanging from an exposed PT rod in the debris of the collapsed structure.

(Note to others: MikeG probably is not going to see this post unless it is quoted. For reasons best left to him to explain. He thinks I'm a big meanie. It is unlikely he has seen any of my posts in this thread.)
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Old 18th March 2018, 05:26 AM   #136
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Originally Posted by quadraginta View Post
You are mistaken. Both in general and in this particular case.


There are different types of PT reinforcing. Steel rods, like rebar only with threads instead of deformations, and stranded cable are used in post-tensioning. I have installed both kinds.

Both systems are being used in this structure.

The bridge slab and canopy are reinforced with PT cable, which I have described in some detail above.

The bridge trusses are reinforced with PT rods.

This is clearly indicated in the proposal .pdf which I have linked to a couple of times up-thread, which explicitly call for PT cables in the slabs, and PT "rods" in the truss members..

It is also clear that the truss members are reinforced with PT rods in the photos linked to up-thread which show a hydraulic ram hanging from an exposed PT rod in the debris of the collapsed structure.

(Note to others: MikeG probably is not going to see this post unless it is quoted. For reasons best left to him to explain. He thinks I'm a big meanie. It is unlikely he has seen any of my posts in this thread.)
Yes, this was explained earlier in the thread.
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Old 18th March 2018, 06:08 AM   #137
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Originally Posted by Captain_Swoop View Post
Yes, this was explained earlier in the thread.

I know.

It seemed to me that MikeG's unequivocal statement that the use of the term "rod" in relation to post-tension was somehow wrong required some reiteration of earlier posts.

(And, thanks. )
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Old 18th March 2018, 03:30 PM   #138
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Originally Posted by quadraginta View Post
It isn't clear that the placement of the transport system was a culprit. "Maybe." is still the most authoritative answer.

I've read through and been following the discussion thread on the engineering board I mentioned up-thread. (It's called Eng-Tips Engineering Forums.) There's some good conjecture there. Yes, it is still conjecture, but some of it is informed conjecture, and thought-provoking.

It helps to look at the truss details page (pg. 115 of the proposal .pdf) to follow what they are talking about.

In short (if that's possible) their prevailing theory is that the rod tendons in the endmost truss members (#1 and #11. #11 is the one at the end which failed) were actually only there to provide support for the move itself, and needed to be de-tensioned after the move. This is based on the fact that in the schedule for the truss members on pg. 115 of the proposal .pdf there are no specifications for any rod tendons for those two truss members as part of the structure. The idea being that these truss members were designed to be in compression, and therefore no tension reinforcing was required.

This is where the conjecture starts getting thick. The question is, what exactly were they trying to do with the PT rod they were working on? By all appearances it was one (possibly of two, with the other having its live end at the bottom of the truss segment) which was in truss member #11.

It is possible that this was part of the de-tensioning for after the move, when PT rods were no longer required or even recommended in that truss member, and that when they were trying to loosen the nut on the PT rod they over-tensioned it. (You have to pull 'em a little bit to get them loose, that's always the most hateful part about de-tensioning any PT, whether it is rebar or cable.)

It does seem likely, looked at some of the photographic enhancements in the thread, that truss member #11 buckled and failed, for whatever reason.

It is possibly related to the cracks which were seen. Maybe they decided that re-tensioning that PT rod would help with the cracks that were seen.

It is entirely possible that some damage was done as a result of the changed placement of the transports, and that is what started the cascade of issues which resulted in the collapse.

There's still more to be learned about the whole thing, but I am afraid we are approaching the point where such information isn't going to be as easily accessible as what we have learned so far.
Thank-you

Your posts in this thread have pretty much cleared up all the questions I had about this incident.
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Old 18th March 2018, 04:02 PM   #139
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How about a screw up in the changes to the implementation.

The original design was for there to be a large steel plate on top of the transports to spread the load. The transports to be placed at each end at specific points designed to take the load. Someone decides it would be cheaper and easier to leave out the plates. That is checked and passed as still being safe. It the turns out the transport at one end can't go there and had to be moved inboard. If the plate was still there it would have been ok and was given the all clear.

Now you have the bridge moved with the transport in the wrong place and no plate to spread the load. It is in that video.
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Old 18th March 2018, 04:46 PM   #140
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If the problem is what I think, that the unsupported end sagged in a direction it was never intended to be loaded, the plate wouldn't have helped.
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Old 18th March 2018, 05:07 PM   #141
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Originally Posted by a_unique_person View Post
How about a screw up in the changes to the implementation.

The original design was for there to be a large steel plate on top of the transports to spread the load. The transports to be placed at each end at specific points designed to take the load. Someone decides it would be cheaper and easier to leave out the plates. That is checked and passed as still being safe. It the turns out the transport at one end can't go there and had to be moved inboard. If the plate was still there it would have been ok and was given the all clear.

Now you have the bridge moved with the transport in the wrong place and no plate to spread the load. It is in that video.

It is a plausible conjecture and certainly may have relevance to the effects which led up to the collapse.

I'd be hesitant to go any farther than that. There are other possibilities which may be equally if not more significant. It is entirely possible that the changes to the transport plan had little or nothing to do with the failures which led up to the collapse.

There is the possibility that unanticipated design issues were the primary component of the failure. There has been a fair amount of concern within some of the chatter among structural engineers about problems intrinsic to concrete truss designs.

The concept of having a truss member whose primary design function is to be in compression, but is temporarily required to be in tension for the purposes of transport (which is what was being done with truss member #11, the one which seems to be the proximate failure point) is also an area in question, although the one at the other end of the bridge (#1) was treated the same way, and doesn't seem to have been a problem. At least not yet.

Even the cracks which were seen and reported, which so much has been made of, may or may not have any relevance at all. Concrete cracks. It is the nature of the beast. Steps are even taken as a part of normal design considerations to control and dictate where cracking occurs, mostly for cosmetic reasons.

Some cracking can be significant, indicating structural issues which need to be addressed. Other cracking is perfectly normal, to be expected, and means nothing as far as the safety and integrity of the structure is concerned. I sure would like to see some photos of those cracks they've been talking about. I am sure that such photos exist.

There's a lot left to be learned, and it may turn out that none of the things which loom so large in all the conjecture going on right now in the lay press are going to end up being the real "smoking gun".

Then again, one or more of them might.
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Old 18th March 2018, 05:25 PM   #142
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Originally Posted by Trebuchet View Post
If the problem is what I think, that the unsupported end sagged in a direction it was never intended to be loaded, the plate wouldn't have helped.

It would have if it was sufficient to provide the support which may have been required. I think the term "plate" might be getting used pretty loosely, and shouldn't be over-analyzed, at least not yet.

Since this was a design-build team project with the actual bridge designers being one of the two partners of the team, it is not out of line to surmise that they were closely involved in the moving procedure and any changes being made to it. The whole concept of off-site assembly for this build was, after all, their idea.

Because of that, I have to suspect that the relocation of the support structure lift points for the move was not done casually and without any additional input from them Their engineers, the ones who designed the bridge with transport as an integral part of its structural considerations, would have been involved in the changes.

It seems that the change in the nature of the loading on the end truss members due to the transport plan was anticipated by the designers. This seems to be why there were bar tendons in those end truss members which were not part of the truss member schedule. They were intended to allow those two end members to perform in tension during the transport procedure, and then be de-tensioned after the move was completed so that they would be performing in the compression mode which they needed to be in for the final support of the bridge.

It doesn't seem clear whether the operation which was going on when the failure occurred was de-tensioning, or as some reports have claimed, re-tensioning of those tendons, or why it was being done at this stage, nearly a week after the move was being completed.

All questions to which we have no answers. Yet, anyhow.
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Old 18th March 2018, 08:12 PM   #143
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This reminds me of the "Westgate Bridge" in Melbourne.

https://en.m.wikipedia.org/wiki/West...ridge#Collapse

There was a problem but the attempt to fix it was a disaster.
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Old 19th March 2018, 12:25 AM   #144
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I was living in Melbourne when that happened. That was a concrete box girder bridge under construction. I was way too young to follow the story of its failure, other than the resulting carnage.
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Old 19th March 2018, 01:37 AM   #145
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I can still remember the day at school when we heard about it. Found it hard to believe that a bridge that big in such an important project could just collapse.

Sometimes the engineers just have to face up to the fact that they have a problem. They can't just use a hack to fix it and that the proper solution is going to be very expensive and embarrassing.
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Old 19th March 2018, 03:50 AM   #146
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Originally Posted by Trebuchet View Post
The TL/DW on that, as I understand it:
The rod in question may have already been overstressed and was yielding. They saw it was loose, didn't understand why, and were tightening it further, causing it to snap. It's a fairly reasonable hypothesis. It'll probably take six months or more before we have an official result.
Seeing any structural component out of spec and not closing the road was a serious mistake. Something was going wrong and bandaiding it is a way to cause a collapse as we see here.

I am reminded of Box Girder bridge collapeses where there was buckling and the on site engineer ordered it straightened instead of realizing that something was seriously wrong.

http://www.engineersjournal.ie/2016/...idge-collapse/
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Old 19th March 2018, 04:04 AM   #147
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Originally Posted by a_unique_person View Post
I can still remember the day at school when we heard about it. Found it hard to believe that a bridge that big in such an important project could just collapse.

Sometimes the engineers just have to face up to the fact that they have a problem. They can't just use a hack to fix it and that the proper solution is going to be very expensive and embarrassing.
But that was a non unique problem with box girder bridges.

"On 6 November 1969 in Vienna, Austria, three loud bangs punctuate the evening air. The bangs originate from the banks of the River Danube where the construction of the Fourth Danube Bridge is under way. The 412m long continuous box-girder bridge hasn’t collapsed, but it is hanging in the air, kinked and distorted [1].

Seven months later and almost 2,000km away, one of the longest bridges in Europe is under construction near the seaport of Milford Haven in Wales [1]. It too is a continuous box-girder bridge with seven spans. The free cantilevering erection method has been adopted for its construction. On 2 June 1970, one of its cantilevered spans is stretching 61m over the River Cleddau when it suddenly buckles over a support and collapses. There are four fatalities.

Fast-forward to 10 November 1971, and we find ourselves in West Germany, where a continuous box-girder bridge over the River Rhine is under construction. It is the first all-welded bridge in West Germany, it has a central span of 236m, and it too is being constructed using the free cantilevering erection method. Then its bottom chord suffers a compression failure and the bridge buckles – not over the support, but halfway along the cantilevered span. It hangs like a broken-necked animal – its head in the river [1]. This time, there are 13 fatalities."

This was why I was so shocked that the on site engineer didn't close the road.

http://www.engineersjournal.ie/2016/...idge-collapse/
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Old 19th March 2018, 04:51 AM   #148
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Originally Posted by quadraginta View Post
Crowds of people are also where you really don't want an engineering failure. The bad press is murder.
I would think all the dead people would be the murder part.
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Old 19th March 2018, 05:03 AM   #149
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Originally Posted by MikeG View Post
It would have been perfectly possible, as I said previously, to have a simple steel girder construction, much narrower, and without the tower & suspension stays....maybe 10% of the price. This was a $14 million+ budget.
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Old 19th March 2018, 05:12 AM   #150
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Originally Posted by Captain_Swoop View Post
Publicity picture of the bridge with construction info.



http://i821.photobucket.com/albums/z...psfwlgad6l.jpg
That seems quite the structure to allow people to cross over a road.
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Old 19th March 2018, 05:59 AM   #151
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As someone already commented it's as much a statement as it is a bridge.
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Old 19th March 2018, 06:02 AM   #152
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Originally Posted by Captain_Swoop View Post
As someone already commented it's as much a statement as it is a bridge.
And now it is an even bigger statement. Far more than it ever would have been as a bridge.
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Old 19th March 2018, 01:53 PM   #153
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Originally Posted by ddt View Post
I was wondering about that too. How is a (pedestrian) bridge over a road different than a (car) bridge over the busiest river in NW Europe? Here's some pictures of the bridge put in place near my home, Nov 2013. I'm not in the construction business, so I may be overlooking a simple explanation, but the idea to build the bridge off-site and then sail/drive it into place doesn't seem very revolutionary to me.
There was an automobile overpass built that way in Denver a few years ago, the Pecos Street bridge over I-70. I lived nearby at the time and watched much of the process, in which the old bridge was demolished, dirt and steel plates were put over the interstate to protect it while the bridge was moved and the prefabricated new bridge was moved into place and set, then the dirt and steel plates removed, over a three-day weekend.
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Old 19th March 2018, 02:29 PM   #154
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Originally Posted by Captain_Swoop View Post
As someone already commented it's as much a statement as it is a bridge.
The university wanted to make a statement because they consider themselves a leader in ABC -- Accelerated Bridge Construction technology. They made one, all right.
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Old 20th March 2018, 04:00 AM   #155
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Snopes is commenting on some of the 'fake news' swirling around the collapse.

Quote:
After a devastating pedestrian bridge collapse at Florida International University on 15 March 2018, the National Transportation Safety Board opened an investigation in order to determine exactly what went wrong and who was ultimately responsible for the disaster.


Some corners of the Internet couldn’t wait for the results of this report, however, and claimed that the true culprit was painfully obvious: women.
https://www.snopes.com/fact-check/wa...idge-collapse/

To put it simply, the company was not 'all-female' and making claims like this are as wrong as something I saw online where someone was claiming that they had put an unqualified person in charge of the project because they wanted to be 'inclusive'.
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Old 20th March 2018, 07:52 AM   #156
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I'm surprised they aren't blaming Obama or Clinton yet.
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Old 20th March 2018, 09:04 AM   #157
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Originally Posted by Trebuchet View Post
I'm surprised they aren't blaming Obama or Clinton yet.
Patience, Grasshopper.

They're following a lead that suggests that the second assistant head tool wrangler may have once voted Democrat five years ago.

That'll make the connection.
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Old 25th June 2019, 02:26 PM   #158
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Originally Posted by ahhell View Post
This is a strong possibility. My bet is on some change do design that occurred during construction. Mostly because most structural failures that occur during or shortly after construction are due to the unforeseen consequences of such changes.

Most such projects are overhyped. Its generally the builders responsibility to support structures during construction. Most construction contracts clearly state that as well. The design engineer should understand how the project can be built but the typical don't provide that plan to the builder.




It's pretty difficult for that to go unnoticed during construction. The truck arrives with a ticket that lists the concrete mix design and relevant specified properties. It under goes visual inspections prior to placement and their are regular samples taken for later testing.

Granted, you have to wait 28 days to test those samples.
I was wrong, it was a bad design. Several independent reviews missed that it was a bad design and when cracking occurred the Engineer failed to recognize that it was structural in nature.

Quote:
The report details a catalog of errors ranging from a “deficient” design by Tallahassee-based FIGG Bridge Engineers that led to structural failure, to inadequate oversight by two engineering consulting firms that were supposed to act as a backstop on design and construction, Louis Berger and Bolton Perez and Associates, and a fatal attempt by FIGG to close the cracks that triggered the collapse.

Read more here: https://www.miamiherald.com/news/loc...#storylink=cpy
Osha Report if you are curious.
https://www.osha.gov/doc/engineering/pdf/2019_r_03.pdf

Edit to add, I've done some more reading. There's some serious negligence on the part of multiple parties in this. There were 1 to 2 inch wide cracks days before the failure.

Last edited by ahhell; 25th June 2019 at 02:51 PM.
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Old 1st July 2019, 08:22 AM   #159
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Originally Posted by ahhell View Post
I was wrong, it was a bad design. Several independent reviews missed that it was a bad design and when cracking occurred the Engineer failed to recognize that it was structural in nature.



Osha Report if you are curious.
https://www.osha.gov/doc/engineering/pdf/2019_r_03.pdf

Edit to add, I've done some more reading. There's some serious negligence on the part of multiple parties in this. There were 1 to 2 inch wide cracks days before the failure.
Hmm I wonder if the Engineer of Record in that is going to prison for manslaughter.
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Old 1st July 2019, 09:21 AM   #160
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Originally Posted by ahhell View Post
Edit to add, I've done some more reading. There's some serious negligence on the part of multiple parties in this. There were 1 to 2 inch wide cracks days before the failure.
I've been digging a bit through the report. I'm no expert, and I know that concrete can crack without it being a problem. But some of those cracks... wow. They look bad. Really, really bad. You can see obvious displacement between the two sides.
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