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re: What the hell is wrong in Florida? - The bridge collapse is puzzling on a number of levels
Posted on 3/16/18 at 8:49 am to NYNolaguy1
Posted on 3/16/18 at 8:49 am to NYNolaguy1
Cool design but seems less forgiving that a standard design with support underneath.
Seems like a small frickup on the support cabling could cause a load shite and Max out the unbalanced side really quickly causing a quick and unannounced catastrophic event.
That and if it wasn't design to bow at all that would basically cause the bottom to rip open and the top to compress and aide in the bottom ripping apart. Accelerate the collapsing. Double the fail.
Man that's so sad.
Too bad they didn't continue to support underneath while they retightened everyting. Reports said they were doing some cable work. Dunno
Seems like a small frickup on the support cabling could cause a load shite and Max out the unbalanced side really quickly causing a quick and unannounced catastrophic event.
That and if it wasn't design to bow at all that would basically cause the bottom to rip open and the top to compress and aide in the bottom ripping apart. Accelerate the collapsing. Double the fail.
Man that's so sad.
Too bad they didn't continue to support underneath while they retightened everyting. Reports said they were doing some cable work. Dunno
This post was edited on 3/16/18 at 8:51 am
1
Posted on 3/16/18 at 9:33 am to ChineseBandit58
Looks like such a simple issue, but I can't believe it really is.
The center tower is the support. Imagine building the Golden Gate bridge with just the roadway first, then adding the suspension cables.
Even if this was OK for the initial installation, I can't see any scenario where it would be OK to leave it this way for an extended period while non-protected traffic is all around it. If it is structurally sound enough to stay intact during that, then the support would be redundant.
Typical news, though. CNN all over how the thing is designed for a Category 5 hurricane, so (gasp) how could it have already failed? Well, because it was not finished.
To me (undergrad ME, but still an amateur), the central issue seems to be why the central support tower was not in place and some amount of tension on rods/cables before opening it up to traffic.
The center tower is the support. Imagine building the Golden Gate bridge with just the roadway first, then adding the suspension cables.
Even if this was OK for the initial installation, I can't see any scenario where it would be OK to leave it this way for an extended period while non-protected traffic is all around it. If it is structurally sound enough to stay intact during that, then the support would be redundant.
Typical news, though. CNN all over how the thing is designed for a Category 5 hurricane, so (gasp) how could it have already failed? Well, because it was not finished.
To me (undergrad ME, but still an amateur), the central issue seems to be why the central support tower was not in place and some amount of tension on rods/cables before opening it up to traffic.
Posted on 3/16/18 at 9:38 am to TigerTattle
quote:
U.S. Sen. Marco Rubio tweeted late Thursday that the cables that suspend the bridge had loosened and the engineering firm ordered that they be tightened. "They were being tightened when it collapsed," he said on Twitter.
Posted on 3/16/18 at 9:48 am to tiger7166
quote:
South Florida makes Louisiana government look like a JV corruption team
Disagree. They make us look competent, but no group on this Earth makes us look less corrupt by comparison.
Posted on 3/16/18 at 9:49 am to TrueTiger
quote:
Now of course it is a lawyer's bonanza.
So are you saying it is a bad thing that the families of the people crushed to death will be able to sue?
Posted on 3/16/18 at 9:55 am to junkfunky
quote:
U.S. Sen. Marco Rubio tweeted late Thursday that the cables that suspend the bridge had loosened and the engineering firm ordered that they be tightened. "They were being tightened when it collapsed," he said on Twitter.
From local news.
quote:
FIU touted it as the largest pedestrian bridge in the nation to ever use the innovative method. When the bridge collapsed, the tall tower that was designed to hold the cables attached to the platform had not been installed.
What were they being tightened TO? This is the kind of unqualified claim I would not be making unless I knew for sure.
Posted on 3/16/18 at 10:05 am to ChineseBandit58
My understanding is that the bridge was basically complete and had been inspected by the engineers. During the inspection they noted that some fasteners had loosed and needed to be tightened. The construction company was in the process of tightening them when the bridge collapsed. That is what the injured workers were doing when it fell. The engineers had approved opening the roadway.
Posted on 3/16/18 at 10:12 am to Ag Zwin
quote:
What were they being tightened TO? This is the kind of unqualified claim I would not be making unless I knew for sure.
The cable stays that attach to the panel points (where the vertical and diagonal beams meet at the top deck) weren't in place yet. Those don't get tightened anyway, once they're loaded with the weight of the structure, people, etc. they are "tightened" by gravity. They were tightening the post tension cables in the precast, not any type of suspension cabling.
Posted on 3/16/18 at 10:23 am to NYNolaguy1
It looked to me to that the compression forces on the top chord transferred over to the pilasters on the ends and a connection of the pilaster to the pedestal failed. Once that connection failed the load shifted to the bottom chord and platform. Looking at the real-time collapse video, it looks like the platform broke textbook where shear forces are at their highest.
Posted on 3/16/18 at 10:23 am to junkfunky
quote:
The cable stays that attach to the panel points (where the vertical and diagonal beams meet at the top deck) weren't in place yet. Those don't get tightened anyway, once they're loaded with the weight of the structure, people, etc. they are "tightened" by gravity. They were tightening the post tension cables in the precast, not any type of suspension cabling.
That makes sense, but would you describe these as "The cables that suspend the #Miami bridge"?
To me, that description is solely for the supports from the central tower.
May be semantics, but Little Marco's tweet would probably lead 90% of people to think he was referring to the central suspension.
Posted on 3/16/18 at 10:27 am to Ag Zwin
quote:
What were they being tightened TO?
Probably tightening the post tension cables in the top slab/chord.
This post was edited on 3/16/18 at 10:29 am
Posted on 3/16/18 at 10:30 am to ChineseBandit58
Wonder how much affirmative action the engineering firm has?
Probably none but we as hell will never hear about it if they do
Probably none but we as hell will never hear about it if they do
Posted on 3/16/18 at 10:39 am to Ag Zwin
quote:
That makes sense, but would you describe these as "The cables that suspend the #Miami bridge"?
Not at all, which is why I was laughing.
quote:
To me, that description is solely for the supports from the central tower.
Correct
quote:
May be semantics, but Little Marco's tweet would probably lead 90% of people to think he was referring to the central suspension.
Correct again
Posted on 3/16/18 at 10:41 am to NYNolaguy1
quote:
Probably tightening the post tension cables in the top slab/chord.
There's a picture of a strand jack I saw in the OT thread yesterday.
ETA:
This post was edited on 3/16/18 at 10:43 am
Posted on 3/16/18 at 10:44 am to junkfunky
quote:
I would start the investigation there, especially with active traffic underneath.
This post was edited on 3/16/18 at 10:45 am
Posted on 3/16/18 at 10:51 am to NYNolaguy1
quote:
I would start the investigation there, especially with active traffic underneath.
Yep. We don't do too many PT designs anyway but they always make me nervous because of how much faith you have to put in the contractor.
Posted on 3/16/18 at 10:51 am to ChineseBandit58
If all FIU students were issued Jet Packs at state expense, we wouldn't have this problem.
Posted on 3/16/18 at 11:03 am to junkfunky
quote:
We don't do too many PT designs anyway but they always make me nervous because of how much faith you have to put in the contractor.
Same. All of our designs are traditional CIP or maybe using lightweight concrete depending on the application. I would much rather work with an exotic design mix w/ admixtures to get a high f'c, than get nervous with PT.
Theres way too many unknowns between fabrication in the shop, misplacement of the strands, weak concrete, not to mention getting the means and methods to erect it.
That said I primarily work with buildings and IBC/ACI/AISC, so AASHTO is completely foriegn to me, other than the 1% I learned when I took my PE, so maybe the bridge guys are more comfortable with it.
Posted on 3/16/18 at 11:13 am to junkfunky
That's some tragic irony in that pic.
Posted on 3/16/18 at 11:17 am to starsandstripes
quote:
just a conspiracy to take david hogg and his beta friends out of the news cycle.
Stupid. How is David Hogg a beta? Youre an idiot. Truly
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