Reply
 
Thread Tools Display Modes
  #1  
Old 03-15-2018, 02:11 PM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Instant bridge--just add disaster.

Florida International University installs an "instant bridge" in one morning. It lasts a whole 5 days before it falls on cars and pedestrians, killing an unknown number of people.
  #2  
Old 03-15-2018, 02:17 PM
jz78817 jz78817 is offline
Member
 
Join Date: Aug 2010
Location: Under Oveur & over Unger
Posts: 11,099
it was supposed to be completed in 2019 and be cable-suspended. what the hell did they think was going to support it in the meantime?
  #3  
Old 03-15-2018, 02:21 PM
FairyChatMom FairyChatMom is online now
I'm nice, dammit!
Charter Member
 
Join Date: Aug 2000
Location: Southern Merrylande
Posts: 38,781
Sounds like some civil engineer slept thru his statics class...
  #4  
Old 03-15-2018, 02:24 PM
gnoitall gnoitall is online now
Guest
 
Join Date: Jul 2009
Posts: 5,717
Nauseatingly ironic quote from the article:
Quote:
Before Saturday’s installation, FIU said the method of overall installation would significantly reduce the risk to workers, walkers, drivers and minimized traffic disruptions for construction.
Damn thing didn't even last a week.

I'm intensely curious what the engineering investigation will turn up. I hope it doesn't degenerate into a counterproductive finger-pointing party.
  #5  
Old 03-15-2018, 02:27 PM
jz78817 jz78817 is offline
Member
 
Join Date: Aug 2010
Location: Under Oveur & over Unger
Posts: 11,099
Quote:
Originally Posted by FairyChatMom View Post
Sounds like some civil engineer slept thru his statics class...
and could be held personally liable (civil/criminal) if said engineer signed off on this as a PE.

Quote:
Originally Posted by gnoitall View Post
Nauseatingly ironic quote from the articleamn thing didn't even last a week.

I'm intensely curious what the engineering investigation will turn up. I hope it doesn't degenerate into a counterproductive finger-pointing party.
it wasn't nearly finished. it was meant to be a cable-supported bridge; one of the stories on the Miami Herald has a rendering of what it was supposed to look like. It appears they set the span into place across the end supports, but didn't adequately support the span elsewhere while it was waiting for the cable suspension to be built.

Last edited by jz78817; 03-15-2018 at 02:29 PM.
  #6  
Old 03-15-2018, 03:11 PM
Typo Negative Typo Negative is online now
Guest
 
Join Date: Mar 2000
Location: 7th Level of Hell, Ca
Posts: 16,558
[QUOTE=jz78817;20847226]nnn
__________________
I believe that if life gives you lemons, you should make lemonade. And try to find somebody whose life has given them vodka, and have a party.
- Ron White

Last edited by Typo Negative; 03-15-2018 at 03:15 PM. Reason: bah
  #7  
Old 03-15-2018, 03:46 PM
Machine Elf Machine Elf is online now
Guest
 
Join Date: Feb 2007
Location: Challenger Deep
Posts: 10,751
Quote:
Originally Posted by jz78817 View Post
and could be held personally liable (civil/criminal) if said engineer signed off on this as a PE.
That depends on who screwed up. If he had a solid design and assembly plan, but it wasn't followed, then he's off the hook. Something like that happened in Colorado in 2004, when a bridge girder buckled and collapsed during construction, decapitating the occupants of a car on the highway below it. The design was fine, but the construction crew screwed up the installation.
  #8  
Old 03-15-2018, 04:17 PM
Merneith Merneith is offline
Guest
 
Join Date: Apr 2000
Location: The Group W Bench
Posts: 6,476
The Mayor says that there was some sort of stress test going on today. They didn't stop traffic for it.

https://twitter.com/MiamiHerald/stat...87317606625280


Miami Herald

Verified account

@MiamiHerald

UPDATE: "There was some sort of test going on this morning," says Miami-Dade Mayor Carlos Gimenez. "Some kind of work was going on at that bridge, a stress test."
  #9  
Old 03-15-2018, 04:43 PM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Here is a fairly high-rez photo. Looks like one of the end supports snapped (instead of collapsing from the middle, which is what I assumed.)
  #10  
Old 03-15-2018, 05:18 PM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
Here is a time-lapse video of the span being raised and moved into place last Saturday.

It's a cable-stayed bridge, but it looks like the entire span was brought into place and installed without the cables in place, or any other support. I sure would like to know how they expected it to stay up.

Also, doesn't this seem over-engineered for a pedestrian bridge? Why does it need a set of triangulated trusses and a set of cables?

Last edited by scr4; 03-15-2018 at 05:18 PM.
  #11  
Old 03-15-2018, 05:26 PM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
Quote:
Originally Posted by Darren Garrison View Post
Here is a fairly high-rez photo. Looks like one of the end supports snapped (instead of collapsing from the middle, which is what I assumed.)
Interesting. It's a triangulated structure, so the top & diagonal members would be under compression, and the lower section under tension. And I think the stress would be higher at the ends. So to me, it seems to makes sense that a concrete structure would fail where there is maximum tension, i.e. the lower section at one end.

Disclaimer: my only experience with bridge design is countless hours spent playing Bridge Constructor.
  #12  
Old 03-15-2018, 05:27 PM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Quote:
Originally Posted by scr4 View Post
Here is a time-lapse video of the span being raised and moved into place last Saturday.
Wow, the article at that link is kind of cringe-worthy now.
  #13  
Old 03-15-2018, 05:29 PM
Riemann Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 4,351
Quote:
Originally Posted by Darren Garrison View Post
Wow, the article at that link is kind of cringe-worthy now.
I'm surprised that it hasn't been... erm... taken down.
  #14  
Old 03-15-2018, 05:37 PM
wolfman wolfman is online now
Guest
 
Join Date: Mar 2000
Posts: 10,468
Quote:
Originally Posted by Merneith View Post
The Mayor says that there was some sort of stress test going on today. They didn't stop traffic for it.
I think we're gonna have to put that test down as a fail.
  #15  
Old 03-15-2018, 05:38 PM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Quote:
Originally Posted by Riemann View Post
I'm surprised that it hasn't been... erm... taken down.
The comment section is inadvisably still live, too.
  #16  
Old 03-15-2018, 05:41 PM
Riemann Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 4,351
Quote:
Originally Posted by scr4 View Post
It's a cable-stayed bridge, but it looks like the entire span was brought into place and installed without the cables in place, or any other support. I sure would like to know how they expected it to stay up.

Also, doesn't this seem over-engineered for a pedestrian bridge? Why does it need a set of triangulated trusses and a set of cables?
Yes, it's very odd indeed. Surely the cable stays are either essential or superfluous. If the design involves cable stays, how can it make sense to install the complete deck on one side of the central tower without any cables?
  #17  
Old 03-15-2018, 06:10 PM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
This article suggests something may have been dropped onto the bridge:

Quote:
At least one witness has attributed the collapse of a pedestrian bridge in Miami, to a snapped cable. Speaking on Fox TV, eyewitness Jose Mejia says that he saw a blue cable holding equipment in a blue box, snap. It fell onto the pedestrian bridge, causing the bridge to collapse.
  #18  
Old 03-15-2018, 07:40 PM
PastTense PastTense is offline
Guest
 
Join Date: Jan 2013
Posts: 6,335
It's a 950 ton bridge. It's hard to see how a cable falling on it could cause the collapse.
  #19  
Old 03-15-2018, 07:48 PM
Merneith Merneith is offline
Guest
 
Join Date: Apr 2000
Location: The Group W Bench
Posts: 6,476
Wait - was it the box that landed on the bridge or the cable? The bridge itself was supposed to have suspension cables, that weren't installed yet, to bear the weight of the span. If the box was full of construction stuff, then the added weight landing unevenly on a bridge that isn't correctly distributed might have overcome one of the supports.

AIUI, I mean.
  #20  
Old 03-15-2018, 08:10 PM
Riemann Riemann is offline
Guest
 
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 4,351
Since this is Florida, presumably it was engineered to withstand hurricane force winds. Since we're outside hurricane season, perhaps that explains why the span was (in principle) strong enough to be assembled without cable support, with cables to be attached later?
  #21  
Old 03-15-2018, 08:20 PM
Der Trihs Der Trihs is offline
Guest
 
Join Date: Aug 2005
Location: California
Posts: 38,412
Quote:
Originally Posted by PastTense View Post
It's a 950 ton bridge. It's hard to see how a cable falling on it could cause the collapse.
Some speculation I've seen is that the "stress test" was pulling up on certain parts of the bridge, and the cable snapping caused the bridge itself to drop a little. That would be the weight that did the damage.
  #22  
Old 03-15-2018, 10:51 PM
eschereal eschereal is offline
Guest
 
Join Date: Aug 2012
Location: Frogstar World B
Posts: 13,528
I have read that the death toll – presumably motorists below – to be 4, with 10 sent to the hospital.


I found this
"If anybody has done anything wrong, we will hold them accountable," said Florida Governor Rick Scott …
to seem just a little absurd.
  #23  
Old 03-15-2018, 10:53 PM
aceplace57 aceplace57 is offline
Guest
 
Join Date: Oct 2009
Location: CentralArkansas
Posts: 23,390
Catastrophic engineering failures are rare. There are so many redudant systems to prevent a collapse.

I can't imagine how this bridge design passed modern computer modeling and simulation tests.

Some very serious errors occurred either in the design or construction.

I wouldn't be surprised if homicide charges are eventually fired. An error this big is undefendable. I can't recall a catastrophic failure on a new structure before.

The Tacoma Narrows Bridge had a serious flaw. Called old windy for flapping in the wind. But over engineering kept it up for several months.

Last edited by aceplace57; 03-15-2018 at 10:57 PM.
  #24  
Old 03-15-2018, 10:59 PM
aceplace57 aceplace57 is offline
Guest
 
Join Date: Oct 2009
Location: CentralArkansas
Posts: 23,390
Gallopin Gerty

blasted edit time out got me.
  #25  
Old 03-16-2018, 12:28 AM
aceplace57 aceplace57 is offline
Guest
 
Join Date: Oct 2009
Location: CentralArkansas
Posts: 23,390
They were certainly confident a few days ago.

https://www.google.com/amp/s/amp.cnn...rnd/index.html
Quote:
It was designed to withstand a Category 5 hurricane.

Its durability was supposed to exceed 100 years.

It's the first bridge in the world to be constructed entirely of self-cleaning concrete: It's made of titanium dioxide which, when exposed to sunlight, captures pollutant particles from the air and cleans its own concrete surfaces.

It was installed in just a few hours just five days ago, although its construction wasn't finished.
  #26  
Old 03-16-2018, 02:34 AM
russian heel russian heel is offline
Guest
 
Join Date: Jun 2013
Posts: 1,458
Quote:
Originally Posted by aceplace57 View Post
Catastrophic engineering failures are rare. There are so many redudant systems to prevent a collapse.

I can't imagine how this bridge design passed modern computer modeling and simulation tests.

Some very serious errors occurred either in the design or construction.

I wouldn't be surprised if homicide charges are eventually fired. An error this big is undefendable. I can't recall a catastrophic failure on a new structure before.

The Tacoma Narrows Bridge had a serious flaw. Called old windy for flapping in the wind. But over engineering kept it up for several months.
I'm finding these supposed reports (from the Santa Monica Monitor????🙄🙄&#128580 that there was testing taking place WHILE traffic was allowed to pass underneath the bridge and an accident during the test caused the collapse to be highly questionable at best. A complete and shocking engineering disaster in 2018.
  #27  
Old 03-16-2018, 03:31 AM
aceplace57 aceplace57 is offline
Guest
 
Join Date: Oct 2009
Location: CentralArkansas
Posts: 23,390
New information. May be significant if the cables pulled beams off their support columns.

Still, imho redundant systems should have held the bridge in place until engineers could fix the problem or safely take it down.

It's very fortunate that there weren't more deaths.

https://www.cnn.com/2018/03/16/us/br...ida/index.html
Quote:
Senator Marco Rubio, who visited the site Thursday, posted on Twitter: "The cables that suspend the #Miami bridge had loosened & the engineering firm ordered that they be tightened. They were being tightened when it collapsed today." Rubio has been a visiting professor at the university for the past 10 years.

Last edited by aceplace57; 03-16-2018 at 03:35 AM.
  #28  
Old 03-16-2018, 03:39 AM
aceplace57 aceplace57 is offline
Guest
 
Join Date: Oct 2009
Location: CentralArkansas
Posts: 23,390
Some background information.
https://en.m.wikipedia.org/wiki/Redundancy_(engineering)
Quote:
Structures are usually designed with redundant parts as well, ensuring that if one part fails, the entire structure will not collapse. A structure without redundancy is called fracture-critical, meaning that a single broken component can cause the collapse of the entire structure. Bridges that failed due to lack of redundancy include the Silver Bridge and the Interstate 5 bridge over the Skagit River.
  #29  
Old 03-16-2018, 03:51 AM
Lord Feldon Lord Feldon is offline
Guest
 
Join Date: Dec 2010
Location: Central Ohio
Posts: 5,501
Quote:
Originally Posted by scr4 View Post
Also, doesn't this seem over-engineered for a pedestrian bridge? Why does it need a set of triangulated trusses and a set of cables?
It was a "signature" bridge, meaning it was designed to look fancier than it really was.

Last edited by Lord Feldon; 03-16-2018 at 03:53 AM.
  #30  
Old 03-16-2018, 08:58 AM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
Quote:
Originally Posted by Lord Feldon View Post
It was a "signature" bridge, meaning it was designed to look fancier than it really was.
It doesn't look very fancy to me though. It looks like someone wanted a nice simple cantilevered truss bridge like this, and someone else really wanted a tall tower and cables like this, and they compromised and did both.
  #31  
Old 03-16-2018, 09:03 AM
enipla enipla is online now
Member
 
Join Date: Jul 2001
Location: Colorado Rockies.
Posts: 12,076
Reminds me of this - Hyatt Regency walkway collapse. 115 dead. Seems a sort of seat of the pants last minute design change was the cause.
__________________
I don't live in the middle of nowhere, but I can see it from here.
  #32  
Old 03-16-2018, 09:34 AM
DesertDog DesertDog is offline
Charter Member
 
Join Date: Oct 2002
Location: Mesa, Ariz.
Posts: 3,858
While it might or might not have contributed to the collapse, why in hell was a stress test being performed on an uncompleted structure? It would be like testing a box girder while the guy is still welding it: The action tells you nothing about how the structure will perform when it is finished. If the test was done to ensure the bridge would stand until the suspension cables were in place, why in hell was it performed without closing the roadway underneath? IANA engineer but this makes no sense.
  #33  
Old 03-16-2018, 09:52 AM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
Quote:
Originally Posted by DesertDog View Post
While it might or might not have contributed to the collapse, why in hell was a stress test being performed on an uncompleted structure?
"Stress test" does not necessarily mean putting a realistic stress and seeing if it would fail. They could be putting a very small stress and measuring the strain (i.e. measuring how much it deforms under that stress).

It doesn't have to be done on a completed structure. They can (and probably should) test every piece of the bridge to make sure they are up to design spec. At every stage of construction, they can test the unfinished structure and make sure the structure behaves as expected. If they put a tiny amount of stress - or even a negative amount (i.e. lifting a part of the bridge with a crane) and measure the response, that still tells you if the bridge is built to spec so far. And since they are not testing the structure to destruction, there is (in theory) no need to stop traffic under it.

Last edited by scr4; 03-16-2018 at 09:53 AM.
  #34  
Old 03-16-2018, 10:32 AM
BobLibDem BobLibDem is online now
Guest
 
Join Date: Jul 2003
Location: Home 07 NCAA HockeyChamps
Posts: 19,951
Interesting case. Glad it wasn't in my state else we'd be asses and elbows fielding half-baked questions from reporters and legislators.

A brief look at the desired product left me with "wow, way over the top. For a lousy pedestrian bridge they make such a major structure?" Okay, maybe they really want to make a good impression on visitors to FIU.

I've never heard of stress testing a new bridge. For new construction, you've got concrete cylinders and samples of the steel to test in the lab. If the design is sound you'd never think of testing the bridge.

If I had to guess, I'd put my money on the construction staging. Either the structure was not properly evaluated for this particular stage of construction or the plans weren't followed completely. I find it hard to believe the designer was incompetent, generally for projects of this magnitude you're going to hire one of the larger consulting firms with the experience and expertise to not have failures like this.
  #35  
Old 03-16-2018, 10:39 AM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Quote:
Originally Posted by enipla View Post
Reminds me of this - Hyatt Regency walkway collapse. 115 dead. Seems a sort of seat of the pants last minute design change was the cause.
And I thought about this one. I had several relatives at that race--they weren't on the bridge, but were still on-site to see the chaos afterwards.
  #36  
Old 03-16-2018, 10:43 AM
Mangetout Mangetout is offline
Charter Member
 
Join Date: May 2001
Location: England
Posts: 57,350
The bridge was designed with a pylon and support cables - Seems to me as though they took the temporary supporting structures away before they added the permanent supporting stuff.

-Except I can't believe it's that simple, but I also can't believe the pylon and cables were purely decorative - so if they're required, and they're not there, then the structure is at risk of failure.
  #37  
Old 03-16-2018, 10:43 AM
CarnalK CarnalK is online now
Guest
 
Join Date: Jul 2000
Posts: 14,582
Maybe it's confirmation bias on my part, but this kind of fuckup seems to happen more with pedestrian bridges. Like someone is thinking "oh, it's not like a REAL bridge, not like it has to hold up a truck".
  #38  
Old 03-16-2018, 10:56 AM
BobArrgh BobArrgh is offline
Guest
 
Join Date: Jun 2009
Posts: 1,355
I read an article today that said that the engineering company that designed the Florida bridge also designed a bridge in Virgina ... that collapsed during construction.

http://wtkr.com/2018/03/15/local-bri...lorida-bridge/
  #39  
Old 03-16-2018, 11:04 AM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Here is an 80 page PDF on the proposal for the bridge.
  #40  
Old 03-16-2018, 11:32 AM
jz78817 jz78817 is offline
Member
 
Join Date: Aug 2010
Location: Under Oveur & over Unger
Posts: 11,099
Quote:
Originally Posted by BobArrgh View Post
I read an article today that said that the engineering company that designed the Florida bridge also designed a bridge in Virgina ... that collapsed during construction.

http://wtkr.com/2018/03/15/local-bri...lorida-bridge/
in that article:

"Construction on the South Norfolk Jordan Bridge was put on hold after a truss used to build the bridge shifted,

doesn't immediately identify the failure as a design flaw; could have been an error in assembling that segment or during construction.
  #41  
Old 03-16-2018, 11:37 AM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
Did some more googling and I think this is one weird-ass bridge design. I had thought that the second "layer" was a roof to shelter pedestrians from weather (well, rain--snow is probably not high risk) but from concept renderings and models I see that it covers only a fraction of the bridge and is there to anchor the suspension cables.

Then I think of the Liberty Bridge in (nearby for me) Greenville, SC. Also a suspension pedestrian bridge with a single row of cables, but cost $4.5 million and has been in use for years. I don't know how much it weighs, but the two "masts" are 28 tons each, and I really doubt that the rest of it adds up to an extra 900ish tons. And it actually looks pretty cool.
  #42  
Old 03-16-2018, 11:39 AM
mikecurtis mikecurtis is offline
Guest
 
Join Date: Feb 2016
Location: chicago
Posts: 1,118
and now everybody's looking at their bridges


Engineers behind collapsed Fla. bridge involved in East Chicago project

Quote:
The same bridge engineers involved with the pedestrian bridge that collapsed in Miami, killing six, are also involved in engineering a bridge in Northwest Indiana.

Figg Bridge Engineers have been involved in the construction of the new Cline Avenue Bridge in East Chicago, parts of which have already been constructed. The $140 million project will replace the old Cline Avenue Bridge, which was closed and condemned in 2009.
. . .

Figg Bridge Engineers has been under fire legally in the past. IN one incident, the Virginia Department of Labor and Industry confirmed that Figg was fined for an incident in 2012. A bridge they designed collapsed onto a railway, injuring some workers. Figg was fined $28,000, but it was later reduced to $9,800.
  #43  
Old 03-16-2018, 11:41 AM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
Quote:
Originally Posted by jz78817 View Post
"Construction on the South Norfolk Jordan Bridge was put on hold after a truss used to build the bridge shifted,

doesn't immediately identify the failure as a design flaw; could have been an error in assembling that segment or during construction.
This article says that for the South Norfolk Jordan Bridge accident,

Quote:
Figg was fined $28,000 by the Virginia Department of Labor and Industry, which found the company had violated several safety rules. It had failed to gain written consent from a manufacturer before modifying a girder used in construction. The company was also cited for not doing daily, weekly, and monthly inspections of the girder; not providing adequate training for using the equipment; and not having certain safety procedures in place for its maintenance and repair, according to the Virginian-Pilot.
The article also talks about a makeshift walkway (for use during construction?) they built in Fort Lauderdale-Hollywood International Airport that collapsed and inured a TSA employee.
  #44  
Old 03-16-2018, 12:48 PM
Philster Philster is offline
Guest
 
Join Date: Aug 2000
Location: Location: Location:
Posts: 10,494
Video of the bridge collapsing:

http://www.miamiherald.com/news/loca...205443304.html

,
  #45  
Old 03-16-2018, 01:20 PM
mcgato mcgato is online now
Guest
 
Join Date: Aug 2010
Location: Hoboken
Posts: 1,223
Quote:
Originally Posted by Machine Elf View Post
That depends on who screwed up. If he had a solid design and assembly plan, but it wasn't followed, then he's off the hook. Something like that happened in Colorado in 2004, when a bridge girder buckled and collapsed during construction, decapitating the occupants of a car on the highway below it. The design was fine, but the construction crew screwed up the installation.
I used to be a programmer for an engineering company. An engineer told about a project that he worked on, a parking garage, that failed shortly after completion. He said everyone involved with the project was sued, including him as professional engineer. That was designer, engineer, suppliers, manufacturers, workers on site, etc. Then they worked through what happened in order to figure out which of the participants was to blame.
  #46  
Old 03-16-2018, 02:16 PM
Skywatcher Skywatcher is online now
Charter Member
 
Join Date: Mar 1999
Location: Somewhere in the Potomac
Posts: 32,374
Quote:
Originally Posted by Mangetout View Post
Seems to me as though they took the temporary supporting structures away before they added the permanent supporting stuff.
Removing temporary supports too soon brought down a partially constructed apartment building near here 45 years ago.

Last edited by Skywatcher; 03-16-2018 at 02:17 PM.
  #47  
Old 03-16-2018, 02:58 PM
Bill Door Bill Door is offline
Charter Member
 
Join Date: Nov 2003
Posts: 4,835
Quote:
Originally Posted by enipla View Post
Reminds me of this - Hyatt Regency walkway collapse. 115 dead. Seems a sort of seat of the pants last minute design change was the cause.
We looked at it in a class I took. What happened was the threaded support rods for the two walkways were originally designed as a single long rod. This made for construction problems as the nuts supporting the top beam had to be turned all the way up the threaded rod. The construction people proposed cutting the support rods in two, so instead of a long rod with one nut supporting the top walkway and a second lower nut supporting the bottom one they'd have two offset rods, with one supporting the top walkway and one supporting the bottom.

They were well within the load factors for the rods, but failed to consider that this modification meant the nuts and beams supporting the top walkway were now also supporting the bottom one.

The engineers took a real beating on that one, and deserved it. Gross negligence, misconduct and unprofessional conduct in the practice of engineering, loss of licenses; the whole works.

See, that's why engineers are so freaking cautious. If you try a last minute design change and it fails, it's deaths and injuries and destruction of property in the millions; loss of licenses and civil and criminal charges, but if the last minute design change works, you get a certificate of appreciation in a handsome plastic frame.
  #48  
Old 03-16-2018, 04:24 PM
scr4 scr4 is offline
Member
 
Join Date: Aug 1999
Location: Alabama
Posts: 14,384
Quote:
Originally Posted by Darren Garrison View Post
Here is an 80 page PDF on the proposal for the bridge.
This appears to be a solicitation for proposals - it's titled "Design Criteria" and lists requirements for the bridge. It doesn't show any specific design.

It contains 18 pages of pictures showing "Design Concept Precedents." I guess these are what they were hoping to get - they're all prettier than the one they ended up with.

Also, almost half of this 80-page document seems to be talking about an elevator.

Last edited by scr4; 03-16-2018 at 04:26 PM.
  #49  
Old 03-16-2018, 04:38 PM
Darren Garrison Darren Garrison is offline
Guest
 
Join Date: Oct 2016
Posts: 6,931
There is an interesting comment on this NYT article:

Quote:
Originally Posted by Some guy called "mekonahe sangnarnahi" in an NYT article
It seems to me that the structure as constructed was okay to support it's own weight. The cables would be needed at a later stage when the rest of the bridge was constructed, prior to opening the bridge for pedestrian loads. The very fact that the structure was fine for five days indicates that there were no issues with the structure itself. Any issues in the strength of the structure would have been conspicuous. Typically in concrete structures strength issues manifest as excessive sagging and/or cracks in the concrete. I haven't seen any reports detailing such issues. I have seen the footage of the actual collapse. The suddenness with which the structure collapsed leads me to believe that there was a sudden loss in capacity, also referred to as a brittle failure. Loss of steel reinforcement leads to brittle failure in concrete structures. Reports seem to indicate that the structure was post-tensioned (PT). PT provides tremendous tensile capacity to concrete. However, loss of PT can lead to a sudden catastrophic reduction in strength as concrete by itself has virtually no resistance to tensile stresses. Based on Sen. Rubio's tweet, I think they were working on adjusting the PT on this bridge when the failure initiated. There are several photos that show a strand jack attached to a PT bar on the collapsed bridge (I believe failure initiated here). It's quite possible that the PT bar was overstressed or there was a failure of the PT anchor leading to a sudden, brittle failure.
  #50  
Old 03-16-2018, 05:38 PM
aceplace57 aceplace57 is offline
Guest
 
Join Date: Oct 2009
Location: CentralArkansas
Posts: 23,390
PT slabs can be scary for construction workers. I was warned many times to never cut or drill into a PT house slab. You can get badly hurt.

The slab is usually stamped with a clear warning (in the garage) or they'll be a sign posted on the wall. PT slabs are used on land with poor structural support. Like a low lying area with fill dirt. The load is spread across a wider area in a PT slab.

I can easily see a bridge failing if one of those rods snapped.

Last edited by aceplace57; 03-16-2018 at 05:40 PM.
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 02:29 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@straightdope.com

Send comments about this website to: webmaster@straightdope.com

Terms of Use / Privacy Policy

Advertise on the Straight Dope!
(Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.)

Publishers - interested in subscribing to the Straight Dope?
Write to: sdsubscriptions@chicagoreader.com.

Copyright © 2018 STM Reader, LLC.

 
Copyright © 2017