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Pedestrian bridge collapse
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mindwaves
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Mar 16, 2018, 02:54 AM
 
http://www.bbc.com/news/world-us-canada-43418898

Picture of completed bridge (not at time of incident)
https://news.fiu.edu/wp-content/uplo...18_DIGITAL.pdf

Tragic event, but I don't want to focus on it, but rather on the accelerated bridge construction, as they say, was used to construct the bridge. In this manner, the bridge was constructed on the side and then craned over and installed in six hours. I've seen this before (on Youtube, at least) and it seems to work well, but not in this case. I wonder if this engineering firm who was in charge of the bridge ever used this construction method before.

Another thing that I would like to mention is that even if that bridge was installed correctly and functioning, that few people would ever use that bridge. There is a crosswalk complete with stoplights about 20 feet away. Yes, people would argue that someone got killed at that crosswalk last year and it is dangerous because people speed, but don't ever underestimate the power of human laziness. What human would walk up a flight of stairs (1.5 story building height, I guess), cross over, and walk down, versus waiting for the stoplight and being careful? Very few people indeed. Pedestrian bridges are usually for a long block where the crosswalk is not handy (or for when there is a barrier that separates the lanes), not when a crosswalk is 20 feet away.
( Last edited by mindwaves; Mar 16, 2018 at 05:01 AM. )
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Waragainstsleep
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Mar 16, 2018, 05:49 AM
 
The bridge had tables to sit and eat lunch etc.
I have plenty of more important things to do, if only I could bring myself to do them....
     
ghporter
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Mar 16, 2018, 11:12 AM
 
The Tamiami Trail through Miami is a notoriously fast and dangerous road. We're talking about a major highway through that part of Miami, with 6 lanes (plus turn lanes) that are very busy most of the day. Crosswalks and lights on 6-lane highways are not sufficient for more than trivial foot traffic. The bridge was intended to connect the campus with an area where a lot of students live, so they could walk to school and avoid both traffic and the costs involved with shuttles, cars, and so on.

The problem does not seem to be with the installation of the span over the roadway. It's too early to even hazard a guess as to what happened, but from the way the thing came down, it looks kind of like what happens when you tap tempered glass on the edge: the object basically disintegrates. I'm hoping to hear a definitive answer for how it actually failed.

Glenn -----OTR/L, MOT, Tx
     
andi*pandi
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Mar 16, 2018, 01:21 PM
 
boston has a similarly designed vehicle bridge that they are now concerned about.
     
reader50
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Mar 16, 2018, 01:40 PM
 
I agree with Glenn, we need to wait on the engineering analysis. It might be the design, or someone mistakenly used standard-strength bolts. Or road vibration splintered the cement foundations, because a wrong mix was used. Too many possibilities, no real data.
     
mindwaves  (op)
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Mar 17, 2018, 07:45 AM
 
Yes, it may be a dangerous road/intersection, but I still doubt anyone would have used the bridge. There is a very similar pedestrian bridge where I live (3 miles away) that is also about 20 feet away from a functioning crosswalk. It is also about 50 feet from a flyover on-ramp. No one uses the bridge still. It is better (or faster) to be careful and take your chances on the crosswalk instead of going up and down stairs.

Now, if they put some barrier between opposing traffic like bushes, then people would be forced to walk up the pedestrian bridge, and then they can actually remove the sidewalk. Some cities do this and its highly effective.

I just read the transcripts of an engineer who reported cracks in the bridge 2 days before the incident, but declared it nothing to be concerned about. Probably not the source of the problem, but interesting nevertheless.

http://www.fdot.gov/info/CO/news/new...e-Collapse.pdf
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ghporter
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Mar 18, 2018, 06:06 PM
 
Here's a link to a dash cam video of the actual collapse: Dash Cam

While it looks like the collapse started where the crane was (just on the leftmost median), the deck/support structure clearly failed at a nearby spot. There was no visible movement of the crane; if it had been supporting the end of the bridge (and it was way too small to do that) it would have bounced all over the place.

The end that failed was indeed the north end of the bridge, where the project engineer in the link in mindwaves' post above said there were cracks. Aside from the whole issue of the FDOT not knowing enough about the project to correctly enforce traffic closures - or prohibit installation of the bridge if needed - the transcript sure sounds sketchy, doesn't it?

Glenn -----OTR/L, MOT, Tx
     
mindwaves  (op)
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Mar 19, 2018, 01:25 AM
 
The video will sure prove helpful in understanding the point of collapse. Definitely doesn't seem to have the crane be connected to the bridge at the point of collapse. I am not sure why you think that the transcript seems fishy. Can you clarify? Seems coincidental to me and probably common to have engineers voice their concerns after a building is constructed so corrective action can take place.
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ghporter
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Mar 22, 2018, 06:34 PM
 
Having a professional say “um” and such so often just sounds fishy to me. You’re calling to explain that you found “something,” but it’s no big deal should be just that: “we found some cracks, but they’re no big deal.” The transcript sure sounds like the telephone equivalent of avoiding eye contact and sort of, kind of, maybe hedging on whether the engineer was doing his job at all.

I’d feel better if he’d said anything straightforward at all. On the other hand, it may just be that the guy was lousy with leaving messages on voicemail. That bugs me, but for a different reason: a professional should be able to express himself about his profession without sounding like he’s making stuff up as he goes. I have to do that in my health care profession every day (all day, sometimes).

Glenn -----OTR/L, MOT, Tx
     
   
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