Diversity Fail? All-Women Engineering Team Blamed for Collapse of Miami Pedestrian Bridge

[RoosGirl]

@RoosGirl

Florida Professional Engineer licence #   34332.  Licence since 1984, expires 2019. 

You can search here:  https://www.myfloridalicense.com/wl11.asp

Oh, Denney is his middle name.  I used it as his first.  That's why nothing was coming up.

[DB]

This stop motion shows where the tendon appears to fail, or at least fail in adhesion to strut, then the other end shoot off the top.

I wonder if it was over tightened and/or with increasing the tension the end anchors failed. Or if they were tightening the wrong support, #11. It would seem that particular support was already in heavy compression, why add more compression to it? The next support over, #10, was being stretched so tensioning it would make sense.

[RoosGirl]

Isn't that in part, what government agencies do with plan checks, inspections, materials tests etc?

I know you really really really want this to be the government's fault, but those kinds of things are generally the responsibility of the EOR to verify and sign off on.  The permitting agencies will set the requirements for what tests are required and what the results of those tests should be, but it is the engineer that is responsible for signing off on them.

[thackney]

I wonder if it was over tightened and/or with increasing the tension the end anchors failed. Or if they were tightening the wrong support, #11. It would seem that particular support was already in heavy compression, why add more compression to it? The next support over, #10, was being stretched so tensioning it would make sense.

I've read reports both that they were tensioning and relieving.  I could see where after transport and put into place, #11 would need additional tensioning.

The following exaggerates the differences from transport to placement in how the trusses work differently in each case.

[DB]

I've read reports both that they were tensioning and relieving.  I could see where after transport and put into place, #11 would need additional tensioning.

The following exaggerates the differences from transport to placement in how the trusses work differently in each case.

Isn't that the other way around? During transport it would need additional tensioning because it was being stretched and the additional tension needed to be higher than the stretch force. Once in place it was being compressed and the tension could be relaxed (we're talking about support #11). Support #10 is exactly the opposite. It looks to me they were adding tension to the wrong support, #11.

[truth_seeker]

I know you really really really want this to be the government's fault, but those kinds of things are generally the responsibility of the EOR to verify and sign off on.  The permitting agencies will set the requirements for what tests are required and what the results of those tests should be, but it is the engineer that is responsible for signing off on them.

You are really, really wrong as to what I want. I want to learn what took place.

The party regarding which we are the LEAST likely to get the entire truth is the government role.

The city/county/state collect building fees, purportedly in part, to insure that lives and property are safe.

I realize the cause might be material failure, bad design, improper procedure, etc. It could be crane operator error. 

[RoosGirl]

You are really, really wrong as to what I want. I want to learn what took place.

The party regarding which we are the LEAST likely to get the entire truth is the government role.

The city/county/state collect building fees, purportedly in part, to insure that lives and property are safe.

I realize the cause might be material failure, bad design, improper procedure, etc. It could be crane operator error.

My apologies.  That is the second or third time you've asked a question or made a statement regarding this collapse that, imo, seemed like you were blaming the government for what happened.

[INVAR]

As was pointed out by serval earlier - the bridge was using brand new 'earth-friendly' and unique material, on top of those who keep bringing the focus to the design itself; no redundancy to carry load weight with a structure totally made out of concrete instead of steel beams. 

From FIU's own brochure:

The new bridge is the first in the world to be constructed entirely of self-cleaning concrete. Titanium dioxide will keep its surface white, remove pollutants from the air, and decompose UV radiation. The titanium dioxide, when exposed to sunlight, captures the pollutant particles from the air and self-cleans its own concrete surfaces. This reduces maintenance. This self-cleaning concrete is considered a promising tool for reducing pollutant load on heavily congested traffic routes.

The main span was built next to Southwest 8th Street using Accelerated Bridge Construction methods being researched at FIU’s Accelerated
Bridge Construction University Transportation Center. These methods reduce potential risks to workers, commuters and pedestrians and minimize traffic interruptions.

Oops.

[DB]

As was pointed out by serval earlier - the bridge was using brand new 'earth-friendly' and unique material, on top of those who keep bringing the focus to the design itself; no redundancy to carry load weight with a structure totally made out of concrete instead of steel beams. 

From FIU's own brochure:

Oops.

The fault may be as simple as the wrong tension rod being tightened crushing the support member around it.

[RoosGirl]

As was pointed out by serval earlier - the bridge was using brand new 'earth-friendly' and unique material, on top of those who keep bringing the focus to the design itself; no redundancy to carry load weight with a structure totally made out of concrete instead of steel beams. 

From FIU's own brochure:

Oops.

I don't think "entirely out of self-cleaning concrete" means what you think it means.  I think it means that all of the concrete used in the project is self-cleaning concrete, as opposed to regular concrete, plus the other materials in it.  It clearly has steel reinforcement (tendons) called out in the design plan.

[edpc]

Make me a sammich!

Be careful what you wish for.  Club sandwiches are load bearing.

[INVAR]

I don't think "entirely out of self-cleaning concrete" means what you think it means.  I think it means that all of the concrete used in the project is self-cleaning concrete, as opposed to regular concrete, plus the other materials in it.  It clearly has steel reinforcement (tendons) called out in the design plan.

From what I am hearing and watching explained by engineers going over this collapse - is that the design itself was flawed.  They are laughing at the absurdity of it. 

The entirety of this "first ever use" of a redesigned truss concept for a concrete span that had no steel beam support structure, was wholly dependent upon the cables inside the concrete trusses for weight load, tension and flexibility.  They keep repeating that with this 'new design' that if just one of those cables became compromised, weakened or stretched/snapped that the entire structure would have collapsed exactly as it did.

They are suggesting that the design seemed more interested in aesthetics than practical safety.

The fact that the span had no support outside of the single trusses after it was placed on the support bases after over stressed cantilevering of the bridge during it's installation, and that they permitted traffic and pedestrians to travel beneath it, was beyond reckless.

[Fishrrman]

I was an "engineer", but one who played with trains, not bridges.

But one thing is clear to me about -this- bridge.

If they replace it, the replacement had ought to be of a time-proven OLDER design that is known to work and be capable of holding itself up, not some new-fangled and untested one...

[BassWrangler]

The design itself was fatally flawed and would have ended up killing a whole lot more people at some point in the future. 

Also - the installation itself was beyond stupid.  No supports above or below - while allowing traffic to run by underneath.

The following video from an engineer is a great examination of the bridge design itself and the collapse.

He explains that the vertical tower and cables were just a "dummy" suspension bridge "look"---NOT the support system for the bridge.

The ONLY support system for the bridge was a SINGLE LINE of "trusses" consisting of V-shape diagonal concrete columns, that have a single cable inside. If the cable in ANY ONE of those fails or breaks - the bridge was going to come down regardless of how or when it failed.

They were apparently tightening the cable on the first truss when the cable snapped, and down she went.

There was no backup for the design, no redundancy of support, only a single column of concrete trusses to hold up the bridge.  No steel in the construction whatsoever, except for whatever cable they had inside the trusses.

It was a disaster just waiting to happen.  I suppose better now than if it was open and operating and it collapsed with a bunch of students walking on it AND cars below it.

! No longer available

great post

[thackney]

Concrete Truss bridges have been in use for a while.  The oldest I know still standing was built in 1915.

https://bridgehunter.com/category/tag/concrete-truss/

[Weird Tolkienish Figure]

Post this on Facebook and see how many angry harpies reply. 

[Bigun]

The fault may be as simple as the wrong tension rod being tightened crushing the support member around it.

@DB

So it would appear but I'm not much on long distance failure analysis.  Maybe the truth will come out sooner or later but I personally wouldn't bet on that either.

[Sanguine]

Post this on Facebook and see how many angry harpies reply. 

Why wouldn't they?  The headline is very misleading.

[the_doc]

Generally speaking, women have talents men don’t and men have talents women don’t, and it has nothing to do with socialization. There actually are gender differences beyond the obvious physical differences.

However, without knowing the specifics here I’m not prepared to say those differences were in play in this case.

A lot of female civil engineers are very competent.

[Elderberry]

NTSB News Release
National Transportation Safety Board Office of Public Affairs
 NTSB Investigation of Bridge Collapse Continues
3/21/2018

https://www.ntsb.gov/news/press-releases/Pages/NR20180321.aspx

MIAMI (March 21, 2018) — NTSB investigators remain at the scene of Thursday’s pedestrian bridge collapse on the FIU campus, focusing on measuring and documenting the critical structures at the north end of the bridge.
Significant developments in the investigation include:

    Investigators secured a contract Tuesday to have a company remove components from the bridge that we believe warrant additional examination and testing. These components include sections of the floor, the canopy, a vertical member and a diagonal member; all from the north end of the structure.  These components were in the area of where the failure occurred. In addition to these components, we obtained additional core samples from this area to supplement the core samples we obtained earlier.
    Shipping the core samples along with some recovered rebar and tensioning rods to the Turner Fairbank Highway Research Center, in McLean, Virginia, for testing and evaluation.
    The investigative team has obtained an exemplar tensioning rod and hydraulic unit used by the construction crew to make tension adjustments to the tensioning rods. These items are also being shipped to the Turner Fairbank Highway Research Center for evaluation and testing.
    The larger bridge components the investigative team is removing, are being stored at a secured Florida Department of Transportation facility, under the control of the NTSB. The additional examinations and forensic deconstruction of these components will occur there.
    The investigative team has confirmed that workers were adjusting tension on the two tensioning rods located in the diagonal member at the north end of the span when the bridge collapsed. They had done this same work earlier at the south end, moved to the north side, and had adjusted one rod. They were working on the second rod when the span failed and collapsed.  The roadway was not closed while this work was being performed.

Ongoing work includes:

    Removal of the post-tensioning device to a temporary storage area and preparing it for shipment.
    Preliminary comparison of bridge schematics to measurements obtained during the investigators’ examination of the collapsed structure.
    Interviews with first responders

While segments of the bridge are being transported to and stored at an FDOT facility, there are no plans to reconstruct the bridge as part of the NTSB investigation into why the bridge collapsed. The nature of the structure and the way it failed make reconstruction impractical.

The next update on the progress of this investigation will likely be the preliminary report. Preliminary reports are generally completed within a few weeks following completion of field work.  Preliminary reports do not contain analysis and do not address probable cause.

[DB]

Thanks for the update.

[RoosGirl]

I happened to strike up a conversation yesterday with one of the principals of one of the forensic engineering firms doing the digging into the collapse.  He is a nuclear engineer, said he was keeping far away from that nonsense and letting the people in his office who know what they're doing complete the investigation.

[roamer_1]

The collapse starts in the span where the workers are tensioning/relieving one of the canopy tendons.

Looks to me like the crane was bearing, and lost hook. Something goes flying off... The stop-action makes it hard to see if the boom bounces...

[RoosGirl]

Looks to me like the crane was bearing, and lost hook. Something goes flying off... The stop-action makes it hard to see if the boom bounces...

I believe the crane was there to support the worker on top.  His harness failed when the bridge fell and that's what you see go shooting up; the worker falls, snaps the harness, worker keeps falling and harness snaps back up.

[DB]

Looks to me like the crane was bearing, and lost hook. Something goes flying off... The stop-action makes it hard to see if the boom bounces...

The crane was likely there to move the hydraulic tensioner and worker using it safely around to the different tensioner locations on the top canopy. The things shooting off at the start of the collapse are likely either the tensioning rod snapping or the support member around the tensioning rod collapsing.