Author Topic: Florida Bridge Collapse  (Read 1097 times)

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Offline LightWtJet

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Florida Bridge Collapse
« on: March 22, 2018, 11:43:16 pm »
This is OFF TOPIC--
Neat ideas on how bridges are built- and one persons theory on what went wrong.

 Prof. Simon says -- When one of the tension rods running from the bottom to the top section was found loose- the team decided to tighten it more. It was thought that rod had been stretched when the jack holding the bridge up was moved to a new position.  When they tried to tension the over stressed rod more- it broke.   Time will tell if this theory is correct.


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Offline rockhouse66

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Re: Florida Bridge Collapse
« Reply #1 on: March 23, 2018, 08:02:40 am »
You would think it would take more than one overstressed rod to bring it down but I suppose it is possible.  I understand that this Alternate Bridge Construction is basically headquartered at FIU's Engineering School and the system is being promoted by them as a result of a Federal Grant.  I'm sure that program has taken quite a hit by this catastrophe.
« Last Edit: March 23, 2018, 02:54:20 pm by rockhouse66 »
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Offline preaction

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Re: Florida Bridge Collapse
« Reply #2 on: March 23, 2018, 02:21:39 pm »
Very good video thanks for posting.
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Offline Chris Teeling

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Re: Florida Bridge Collapse
« Reply #3 on: March 23, 2018, 07:35:50 pm »
Quote
You would think it would take more than one overstressed rod to bring it down but I suppose it is possible

Agreed, A good design will accommodate a single failure mode without catastrophic failure.

 I am not familiar with the design of that bridge but competent structural engineering oversight and addressing items uncovered in an FMEA would be normal practice prior to fabricating or something as critical as a bridge.
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Offline rockhouse66

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Re: Florida Bridge Collapse
« Reply #4 on: March 23, 2018, 08:55:28 pm »
I suppose in a sense you could say it was the "perfect storm" because they had that curb issue which changed the geometry of the support vehicles but ....expletive deleted....they must have had an entire team of engineers who were invested in this project who would monitor such things during installation.  The references to "the specifications" in the video is, in my experience, what happens when someone is passing the buck (or the hot potato).  When you have to go back and read the specs after the fact and/or read the commercial terms of the contract, then it is the start of the blame game rather than the "what did we do wrong?" analysis.  CYA.
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Offline 70cj428

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Re: Florida Bridge Collapse
« Reply #5 on: March 24, 2018, 09:08:35 am »
Quote
When they tried to tension the over stressed rod more- it broke.

On one of the news videos, there's a great shot of about 12 feet of the rod sticking straight out of the concrete support with the hydraulic tensioner still attached. (The rods are slid into tubes and just anchored at the ends, so it's pretty apparent that the rod failed prior to the collapse, If not it would still be anchored in the support member). It seems that with current computer aided stress analyses, engineering design is moving more toward higher stressed components with less of a safety factor built in. This saves money (and weight) in your design but you end up with more critical components in your design. Sometimes, you can't avoid critical components, like cables in a suspension bridge, but it's usually prudent to build in redundancy when you can. I'm especially aware of this as I see both sides of this ( My old profession, Mech. Engineer, my new profession, Firefighter) . Ask any engineer about engineered truss construction and they love it, it's light, rigid, strong overall and cheap. Ask any firefighter about it, they'll tell you about sudden catastrophic failure within minutes of significant fire exposure.....

A good example of this is the World Trade Center collapse(s). those buildings were built with cantilevered  poured concrete floors supported in the center by the elevator towers, and the outer ends supported by the stressed structural steel skin of the building. Great idea as the corrugated steel is light and strong, allowing more usable space and load in the building, and a taller skyscraper. Unfortunately, steel loses a ton of it's strength when it's heated. Someone realized this and came up with a way to start a large fire on the upper floors. Within hours, the steel skin failed, the floors started sliding down the center support and the rest is history. Traditionally constructed buildings generally won't do this. A couple examples, a B25 hit the Empire state building in the 40's in a very similar scenario to the WTC without collapse. Here in Philly, we had a fire on the 22nd floor of a highrise (One Meridian Plaza, google it ....) The fire burnt 8 floors of the building over a full day, and although there were fears of a collapse, the structure withstood the massive fire load. (Unfortunately, we lost 3 firefighters in the incident, after becoming lost on a floor above the fire)

I'm pretty sure I'm preaching to the choir, but sometimes the old way of designing things is better .....

Just rambling.....   John

Offline redscj

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Re: Florida Bridge Collapse
« Reply #6 on: March 24, 2018, 01:21:09 pm »
     Here they've built several overpasses next to the freeway & moved them into placed successfully. Lots of cost & time advantages. I have no training in any of this. But it sure looks like this pedestrian bridge was long & narrow. In my mind I picture all kinds of challenges moving all of the bridge at once without twisting it somewhere. The overpasses that have been done around here are large & quite rigid so easier to move all at once. Could this be an example of a design that was plagued with construction problems from the start? I suspect that I may not live long enough to see the end of the lawsuits over this disaster.
     As for the World Trade towers. I suspect that they didn't have much of a plan. In my mind if there was a plan they would of hit the towers much lower. This would of trapped more people inside & there would of been more load above the fire. So perhaps the collapse would of been sooner. JMHO.
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Offline 70 BOSS 302

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Re: Florida Bridge Collapse
« Reply #7 on: March 25, 2018, 01:29:24 pm »
Undoubtedly built by the low bidder which can sometimes have serious consequences.  With 30 plus years experience dealing with structural engineers it's been my experience that you aren't going to get an once of safety factor built in.  If the calculator says a particular beam will support the weight that's what you are going to get and not a bit more because the other firms competing for the work is using the same engineering standards.

If you design a little safety factor in then suddenly your bid is too high and tossed out by the guy behind the walnut desk making the decision on who gets the contact.  Somebody needs to be charged with negligent homicide and go to jail over this catastrophe.   Just a poor design from the git go in my opinion.  Why not embed pre-stressed arched beams within the concrete walkway rather than a suspension support of what appears to be just a concrete slab with rebar inside :o :o
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Offline Bigfoot

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Re: Florida Bridge Collapse
« Reply #8 on: March 27, 2018, 11:14:23 pm »
Buddy’s gf drove under it 6 minutes before collapse
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Offline rockhouse66

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Re: Florida Bridge Collapse
« Reply #9 on: March 28, 2018, 08:49:32 am »
There is an amazing dash cam video that shows the collapse.  It also shows the traffic light on the other side changing and cars going under just before the collapse.  Some cars held back to wait until there was room on the other side so they wouldn't get stopped underneath but some didn't.  They must have been leery of what they saw going on.  I saw it on the news when I was still in FL so I don't have a link to share.
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Offline rcode

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Re: Florida Bridge Collapse
« Reply #10 on: April 11, 2018, 09:18:48 pm »
Is this the result of "On Line " DEGREES? Pathetic. We will NEVER know who designed this bridge. 

The gullible public takes it up the A&s again......

Offline 69cobrajetrugae2

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Re: Florida Bridge Collapse
« Reply #11 on: April 12, 2018, 07:27:50 pm »
I studied concrete anchors and used a bridge engineering website for my information when tasked to anchor three huge poles to a concrete driveway.  The weak link is the concrete which will pop up with the anchor at the limit of the concrete's PSI rating.  10.000 pound is considered strong, concrete wise.  3/4 inch bolts are good for something in the order of 180.000 PSI.  What's interesting is that anchor bolts that are too close to one another actually weaken the structure which are attached by the bolts because the concrete is compromised.

 Cracks in the concrete set up corrosion which weaken the steel substructure and inspection is impractical since there is no baseline to establish when a structure is ready to fail, not to mention the economic losses of closing and repairing a structure that may not fail for 50 more years.

I believe that maintenance personnel and the quality of the bridges and associated structure's are up to snuff based on the rarity of catastrophic failures versus the number of structures in the country.