Post Tension Failure Florida Bridge Collapse | Engineering EXPLAINED!

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Shared March 16, 2018

THANK YOU FOR YOUR INTELLIGENT ANALYSIS and WILD-ASS THEORIES! I ran a test to see why the post tension rod was sticking out of the rubble. There was a problem with cracking on the pylon side of the bridge. As my homebrew experiment proves the rod must have failed during tensioning just before the bridge collapsed. Engineering Forum http://www.eng-tips.com/viewthread.cf...
Reddit.com/r/engineering


satburn

Although the content is very interesting i'm actually here for the foul language.

1 year ago | [YT] | 1,293

a24396

I really want AvE to narrate "seconds from disaster"

1 year ago | [YT] | 118

Glenn

The bridge identified as a sidewalk.

1 year ago | [YT] | 260

Paul Phillips

You referenced the collapse of the Ironworkers Memorial Second Narrows Bridge in Vancouver B.C. in your presentation above was due to falsework failure. My father knew the first engineer who designed the falsework support for the bridge construction. The base was originally designed using 12X12s laid tight, in four layers to support the upper falsework. The powers in charge considered the design too conservative and used too much timber. The engineer was let go from the project and another engineer was installed to finish the project. The second engineer's design used four layers of 12X12s on 24 inch centers to save materials costs, against the strong objections of the first engineer. After the bridge collapse, my dad found out that the first engineer encountered his replacement in a bar shortly thereafter and beat the living crap out of him. Apparently no charges were laid as a result of the altercation. Thought you'd like to know some background on a bit of B.C. engineering history. Paul

1 year ago | [YT] | 216

losing_myself 2571

Foul language in construction jobs? Apparently the people complaining have never had to deal with this line of work. New subscriber I'll be waiting for the next f-bomb filled episode 👍

1 year ago | [YT] | 131

Eric Gulseth

Anybody that's offended by swearing on these videos have never gotten their hands dirty for a living.

1 year ago | [YT] | 145

Clinton Andrews

"Under certain circumstances, urgent circumstances, desperate circumstances, profanity provides a relief denied even to prayer." — Mark Twain —

1 year ago | [YT] | 228

rhagerty1

If your post tensioned member lasts more than four bours, contact a physician. 😀

1 year ago | [YT] | 149

fusionstar916

That $15 million bridge is going to cost $200 million in legal fees and settlements.

1 year ago | [YT] | 43

Michael Rosenthal

Three worst in the job swear words are :
Should
Easy
And
Fine.
Somebody on that project said" it should be fine" amd wasn't
Don't ever say 'easy' until the check clears.

1 year ago | [YT] | 41

Rivera

There’s an article somewhere on the inter webs with the tittle:
“A Foulmouthed Canadian YouTuber Might Have Solved the FIU Bridge Collapse”

2 weeks ago | [YT] | 2

Internet Privacy Advocate

I see the rod failure as simply a side effect of a horribly poor design. Concrete is not a suitable material for a truss. Had the central single truss been fabricated entirely of steel it would have been more easily and more safely moved. The bridge would have been 90% lighter. The more you study this design the more you realize it was a complete POS. All hype, and no substance. It should have been removed from consideration early in the design concept stage as being totally unproven, and quite impractical. Blaming the collapse on a single bolt gives the engineers an out, but it doesn't excuse them from choosing a worthless design with absolutely no merrit in the fist place. Rather than blaming the catastrophe on a single overly stressed bolt, I put the blame on "group think" where common sense was not only ignored but shunned. All this said, your demonstration was quite informative, particularly when you show how the bolt shoots back out of the hole, and that is seen on the Rosenberg/Figg bridge as well.

1 year ago (edited) | [YT] | 46

AgentFoxMulder

I love this guy, holy shit! Finally, someone with a sense of logic and how to use language to make cogent points. Great great video, thanks for posting and keeping it objective.

1 year ago | [YT] | 3

metaforest

If you are offended by what this man says, it is YOU that have a problem, not him!

1 year ago | [YT] | 18

rickterfied

I found it interesting that this was on the wikipedia page for a couple of hours:
In many bridge truss designs, the triangulated supports are arranged into two or more parallel walls. Among other benefits, this gives some redundant load-bearing paths to help the overall structure survive if any one member fails. In the FIU bridge, there is only a single vertical plane of diagonals along the centerline. There is no backup for any strut. The entire structure is threatened If any one diagonal or joint were to fail. Collapse can be avoided if the remaining joints and members were overbuilt stiffly enough to accept the shifting emergency loads without breaking. Otherwise, the structure continues to sag unchecked to the point where more things fracture or buckle, and the structure folds. Such bridges are called [National Bridge Inventory fracture critical] with each strut being a potential [single point of failure]. That vulnerability is avoided in most new bridge designs.

But not in this case.

1 year ago | [YT] | 18

MrSpeedDemon72

I still don't understand why it was deemed necessary to have a bridge this big and heavy for just foot traffic.

1 year ago | [YT] | 16

Tim Maurer

The first diagonal web member was designed to be a compression member in the completed structure. It was designed to absorb the high shear forces that develop near a support. A late in the game change (Which happens on just about all fast track over budget past schedule projects) required the transporter to be moved one more web panel toward the center of the span. This changed the first diagonal member into a tension member to support the shear of the newly created cantilever end of the bridge. They likely call the engineer and need a "quick" analysis to see if they can do this even though the bridge was analyzed to hell and back in it's permanent position AND "planned" transport position, which unfortunately changed at the ninth hour. The very large tensile forces created in the first diagonal must pass through the post-tensioning tendons. As you see in the video, one of the tendons in the member (The one that has to be tightened from the bottom 12:20)  terminates PRIOR to the "node" or intersection of the rest of the tendons at the blister. The tension in this dead end tendon is resisted by primarily concrete and requires a much lower load to "breakout or crack the concrete." A crack formed and opened over straining and stretching the remaining cable (The one being tightened when it fell). After the bridge was placed back onto its permanent support, the first diagonal goes back into compression and the adjacent web goes back into tension. They go to tighten the cable from the top that was found to be loose (because it had yielded.)  They unknowingly over tighten the loose cable beyond it's strain limit. The imbalance of force causes the crack created earlier to propagate behind "dead end" plate on the first diagonal and a shear failure occurs causing the top deck to fold almost instantly followed by complete loss of shear and bending capacity. PT concrete is not supposed to crack. The pre-compression cause by the steel rods/strand are there to maintain compression or at the very least limit tensile stresses in the concrete to very low values. If a crack forms in through /adjacent to a "node" where intersection forces occur then it could entirely screw up the post-tensioning calculations since the forces have to travel within the material until equilibrium and the guys in the field could be chasing their tail trying to hit target values that can't be achieved without straining the steel past it's breaking strength. Trusses are generally not redundant. All of the members are critical. The job should have been stopped, budgets and schedules blown further, the road should have been shut down until a complete and a thorough analysis of all of the potential failure mechanisms were flushed out. This decision requires GUTS since it could cost a person or Company their jobs. If you can't get ahold of the State when they are on break, then you call the police and have them shut the road down until things can be evaluated and then peer reviewed (Time, money, inconvenience)...No loss of life.

1 year ago | [YT] | 5

Guy Ligier

I believe the unloaded structure should have been strong enough to stand in place had everyone done everything perfectly by the book, but as was said, a disaster often is due to a series of errors.
Error 1: This “first of its kind” bridge is made entirely of “self-cleaning” concrete which contains titanium dioxide. We’re not talking about titanium paint on the outside of the concrete structure, but titanium mixed right in with the concrete. There are many levels of purity for Titanium, and more pure is more expensive. I will bet the materials samples tests will come back that the titanium was substandard.
Error 2: Also, I bet tests will show that the self-cleaning concrete was not mixed thoroughly, and uniformly, and long enough. This resulted in “veins” of overly brittle concrete. That, combined with the too short curing time, left brittle streaks so bad that the concrete’s overall compressive strength was not half of what was expected. (Also, isn’t a giant kiln usually used in making most self-cleaning pre-fab concrete sections?)
Error 3: By not placing the transporter/crawlers at the very ends of the bridge truss, it caused the more slender top member of the truss to be in tension in ways the bridge designers had never intended. When the quickly constructed truss was moved/swung from the side of the road 90 degrees to across the road, the transporters were too far in towards the middle, so the ends of the truss were probably drooping. The crews were probably instructed to tighten the top tensioners more than they would have ever been had the truss been supported from the ends. This over-stressed the compressibility of the crumbly substandard concrete in the top member. The stress from drooping and then over tightening served to cause the brittle veins in the top member to develop deep cracks CLEAR THROUGH the top member like a series of seismic oblique slip faults.
Error 4: Now remove the transporters and start supporting the truss by its ends, and the damaged top member with its slip faults of now powdered titanium concrete is still, remarkably, holding together. Yes, holding together like a half dozen bricks being suspended, held between your two hands. They’ll stay together as long as you keep pushing your hands together. Let up, even a little, and it all falls down. The workers were then probably instructed to loosen the top member tensioners (you can hear that on the video) back to spec, and boom, the top member catastrophically fails along its faults, and its weight and momentum break the truss’s bottom member…and you have 6 crushed to death.

1 year ago | [YT] | 18

Strong's Adventures

I’ve see a post tension cable shoot 400 feet out off a 260 foot building

1 year ago | [YT] | 276

CofRed1228

When trusses are designed, all members within the truss are designed as tension/compression members only. No bending. So like you said, the original transport plan showed the supports at the panel points of the truss or the nodes of the truss. You always load a truss at the nodes...never between nodes. When they moved the SPMT to a spot between nodes, they were asking for trouble.

1 year ago | [YT] | 7