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Only five days after installation pedestrian bridge in Florida collapses

The coming dark age: Less than five days after it was installed at Florida International University a pedestrian bridge has collapsed, trapping and possibly killing an unknown number of people below it.

The story from the weekend describes the bridges construction and installation.

This is a horrible story. Does it, as does the Australian train story from yesterday, indicate a trend? Sadly, I worry that it does. For engineering to fail this badly, this quickly, indicates a level of incompetence or corruption at so many levels it is downright appalling.

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  • Cotour

    A terrible failure of something.

    I found this picture of the bridge during the installation and find the design very interesting in that it is not a symmetrical repeating design of the uprights but the uprights vary in their size and angle as they spread across the span. (?)

  • Kyle

    This is why Civil Engineers are required to take an ethic classes in college, when an electrical engineer cuts corners it might wreck a cell phone battery, but when a civil engineer cuts corners people can die.

    As an engineer, I would like to point out that the central structure wasn’t built yet and none of the suspension cables were in place to hold up some of the loading across the span of the bridge. It could be a fatal design flaw, or the bridge wasn’t built in the correct sequence.

  • Garry

    When I lived in Japan, there was a series of engineering failures in South Korea, including an escalator in a shopping mall, a major bridge, and several others, all within a period of a few months, and all involving fatalities. Needless to say, it went very high profile.

    No design flaws were revealed, but inspectors were paid to ignore use of inferior (cheaper) materials, skipping of critical inspections, etc.

    I can’t remember many cases where a design flaw caused a catastrophic failure like this; it’s usually execution of the design, or lack of maintenance. But we’ll have to see what the engineering investigation reveals.

  • Cotour

    A couple of other observations, the bridge is very flat and does not seem to have any designed in stiffening bow to it. And it appears by some of the comments that this is a “first of its kind” design. I will suppose that that refers to its set of angular single center uprights and “I” beam like top and overall construction configuration resulting in the flat design.

    Kyle refers to “suspension cables”. Do you mean cables hanging over the structure attached to the top and supporting it or Tension cables that run through the main platform “setting” it in tension? If so then why was the bridge either not installed until they were in place or there was a center support that would be removed after they were?

    Its a very long span.

  • Tom Donohue

    The Miami Herald quotes an engineer who believes that the two workers on the bridge when it collapsed were adjusting the cables to fine tune the bridges arc or camber. The article called their actions a “Stress Test” which may not be an accurate description of what was going on –
    I’m curious to know if the tensioning cables only ran underneath or within the lower surface .. or .. were they also routed through the zig-zagging support columns that tied the upper roof-like structure to the lower deck for tensile strength. We sill know more in a few days, I’m sure.

  • Tom Donohue: What I have not been able to determine from the link you provide, or any other stories, is whether the bridge’s tower and suspension support cables were in place. If you look at the last image at this link, describing the bridge’s installation on Saturday, it shows the finished bridge with a single tower from which diagonal suspension cables radiate to provide additional support for the bridge.

    Images of the collapsed bridge today suggest this tower and suspension cables were not yet installed, suggesting that the bridge lacked a significant portion of its support structure. I have not been able to confirm this however.

  • Cotour

    Now I get it.

    I had not seen a rendering of the completed bridge I thought it was just a simple span over the street thats why it looked so / too flat to support itself. It looks like the tower was not up and the tower provided a significant amount of support for the bridge.

    A fatal assembly sequence mistake? That main span is so long, why would it not be temporarily supported in the middle down to the street until the over head was assembled? If the bridge was designed to have an overhead suspension component then why would the main span be set without that crucial support?

    This very unfortunately may well refer directly back to the associate train story, everyone thinks someone else is doing the thinking.

  • Cotour: You are welcome.

  • pzatchok

    I wonder if the concrete was even fully set before assembly?

    It normally doesn’t reach full strength for a month or more.

    One possible scenario…

    Everyone thinks the stuff was poured a month ago so they assemble it and lift it into place, when in actuality it was poured last week, the day before delivery.
    The concrete company was never told to season the parts before shipping them.

  • Max

    From the article,
    U.S. Sen. Marco Rubio, R-FL, said in a Twitter post that: “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.”

    Looking at the motorist picture, there was a crane holding the bridge up until the supports are in place. First section of 175 feet (a total of 320 feet long when done). Not expected to be finished till 2019.
    My guess is the cable clevis failed or ground under the crane wasn’t stable enough to support the weight.

  • Dick Eagleson

    I’ll offer no speculation on causation here; just a little “Evening Pause” of my own that seems magnificently appropriate. Hymn of Breaking Strain written by the great Rudyard Kipling in the last year of his life. Set to music and performed by Leslie Fish and Julia Ecklar.

  • Cotour

    Zman: Thank you.

    Why would you set a 174 foot long bridge across a busy highway, even if it had properly cured, if the design of that component itself did not indicate that it could do what was asked of it, remain in place without the aid of the other main supporting system or a temporary support from the street?

    “Because “I” designed it to do that, my calculations say it can safely stay in place and you could also park a 747 on it without concern”. Or something like that (?).

    Looking at the scene there is a crane there but it does not appear to be there to support anything, its there to lift components to workers doing work on the top, I would say probably assembling the cable attachments but that does not make sense because the tower does not even exist. There was a reported “stress test” being conducted or was just conducted earlier in the morning. So I assume you would have to ask, did that stress test damage or over stress the component in some way?

    The supporting tower is not in place and nowhere in sight as fare as I can see. I assume it might be built off site and was on its way (?). But the tower is huge and IMO it was probably going to be built on site. You can better see the preparations for the building of the supporting tower in this video. Notice the rebar sticking up in the middle of the span, this indicates that the supporting tower was going to be built on site and was the next phase of construction.

    The news report stated that “this was a preferred system of construction”, which I assume means that it was well proven and done many times before the exact same way (?), with the same length of span involved (?) without the supporting tower and cables not in place (?).

    If the tower and cable stays are 50 percent or so of the design in supporting the bridge, then why is the tower not ready before that 174 foot component is set in place? Again, a single 174 foot long reinforced concrete component, even in the configuration of an “I” beam is very long.

    A fatal assembly sequence failure? The first thing to be built in the future? The The tower or the placing of a temporary supporting structure in the center of any long span component.

  • Cotour

    The next question to ask might be:

    If the design is well proven and all materials involved are verified and the span length is not over specification then might the point of attachment and where the span sat on the foundation have somehow failed?

  • Cotour

    An interesting quote, the spin and the politics begin :

    “Munilla Construction Management, which was also involved, also issued a statement of condolence. Bridge collapses in the United States are infrequent despite rising risks associated with aging infrastructure.”

    This “bridge” is not “aging infrastructure”, it was not even “infrastructure”, not until it had a chance to become operational and age anyway. Reaching into historical statistics to explain something that has nothing to do with those statistics is fraudulent.

    AND, we can take a look at this particular picture posted below and notice one very interesting element of the collapse. Notice the one upright is pushed through the top of the reinforced concrete top and the cap / cable attachment point is entirely destroyed, essentially exploded and disintegrated.

    All other uprights are crushed and are below the top structure. A possible cause might be that the top structure failed and the upright pushed through the top destroying the cap / attachment point thereby breaking the structural integrity of the entire span (?).

    Pure speculation.

  • Kyle

    I don’t think the contractors had the right equipment out there temporarily holding the span up.

    Or the engineers could of used the wrong values in their concrete calculations. For all the math we did in school we do a surprising little at the office, most of it is plug-n-chug values into excel. Some of these equations are pretty intense so if you use the wrong strength value it can screw up the results. Experience engineers can determine if the number an equation spits out makes sense or not. But the key word is experience. Some firms have E.I.T. (engineer’s in training) do most of the engineering and then have a PE look over their work and sign off. And if they are as busy as we are they have a lot of other projects with deadlines to review as well. The last time I did any prestressed concrete design was in college, and most of it went over my head. Needless to say its complicated stuff. Combine all of that with the new “self-cleaning” concrete they used and I wouldn’t be surprised if they calculated the wrong yield strength or something and it got overlooked.

  • Andrew_W

    All other uprights are crushed and are below the top structure. A possible cause might be that the top structure failed and the upright pushed through the top destroying the cap / attachment point thereby breaking the structural integrity of the entire span (?).

    Very plausible observation, might fit well with the talk of a support cable going slack.

  • Cotour

    The failure appears to begin at the upper end of the farthest angled upright at the far end of the span. As soon as the upright web support fails, for what ever reason, it all lets loose.

    Go to the 41 sec point of the video and see where the failure appears to start.

  • Cotour

    Andrew W:

    There were no “supporting” cables overhead, the tower was not in place to secure them. There are tensioning cables contained within the slabs that contribute to their strength, but there are no hanging / supporting cables. I think this is becoming a confusion.

  • Andrew_W

    Fair enough, there was talk of a crane acting to support, but yeah, it’s clear on Bob’s latest post that the order of construction was . . peculiar.

  • Max

    Yes, there was a crane on site but why it was not supporting the bridge is a major screwup.

  • pzatchok

    I also have a problem with the roof shape.

    Its just a giant wing.

    Lets just say they had all the concrete calculations correct and they did think this thing could hold itself up untill it was finished.
    What about the wing effect of the roof possibly lifting and dropping the whole thing as each breeze came by?
    At about 150 feet long it must have some effect. Even a few inches movement up and down could double the stressed weight.

  • Cotour


    That crane that you see is probably a 20 ton mobile crane, the bridge weighs 940 tons.

    (The crane was there to facilitate work that the workers on top were in the process of doing, I am not certain that what ever they were doing had anything to do with the collapse)

  • pzatchok

    Upon closer inspection it looks like they took care of the wing shape of the roof.

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