
Florida Pedestrian Bridge Constructed 5 Days Ago Collapses, Multiple Casualties - guardiangod
https://jalopnik.com/florida-pedestrian-bridge-constructed-barely-a-week-ago-1823806666
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niftich
As one can see in the installation video from last weekend, the bridge in
question was the first span of a larger project, in which at least one other
span would have to be installed above an adjacent canal to complete the
crossing.

A rendering [1] shows the completed crossing to be an asymmetric harp-type
cable-stayed bridge, with cables supporting both the portion above the road
(the piece in question), and the piece that's yet-to-be constructed to go
above the water. In this design, it's usually not possible to (temporarily)
install the cables solely on one side of the tower, as the loads on one side
of the tower would collapse the tower.

Therefore, it stands to reason that the cables were either to come into play
at the very end, or if the bridge were constructed by cantilevering out from
the central tower and attaching cables as you go.

In other words, without trying to pass judgment on the cause, the cables are
either a red herring (because the sub-spans are self-supporting), or the
bridge was assembled in a terribly incorrect sequence.

[1] [http://www.miamiherald.com/news/local/community/miami-
dade/w...](http://www.miamiherald.com/news/local/community/miami-dade/west-
miami-dade/article204506084.html)

~~~
Someone
On the rendering, it seems to me that the part over the water is significantly
shorter than the now collapsed part. It also doesn’t look heavier per meter to
me, and the tower seems to be perfectly vertical. That would make it
impossible to fully ‘hang’ the part over the road from the tower.

=> It is quite possible that the span over the road was designed to be self-
supporting.

That would be a non-standard design, but we are so good at building such
bridges that ‘being non-standard’ almost has become the standard.

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danso
Apparently the elevated walkway was installed in less than 1 day (with major
parts of it being pre-fab). But it sounds like it wasn't the complete project,
which was expected to be finished in 2019:

> _Once it’s finished in early 2019, the new pedestrian bridge will link FIU’s
> Modesto A. Maidique Campus directly to the small suburban city of
> Sweetwater, where the university estimates 4,000 of its students live._

[http://www.miamiherald.com/news/local/community/miami-
dade/w...](http://www.miamiherald.com/news/local/community/miami-dade/west-
miami-dade/article204506084.html)

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jandrese
Is it common for pedestrian bridges to be so overbuilt? Given the weight and
span it sounds like it has a cross sectional area of about 75 square feet of
concrete (a little less for the steel components, but still a lot) for a mere
15 foot traffic deck. It's not crossing an especially large span nor need to
carry any substantial weight other than its own, so why does it need to be so
heavy?

Are they expecting trucks to run into it maybe?

~~~
CapitalistCartr
They have to calculate for worst-case scenario. Imagine it were completely
full of people. Dancing. Plus, people do ride motorcycles on them if they can
get them on.

~~~
nugi
I have a few friends that easily outweigh my full size motorcycle.

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AJ007
Are bridges collapsing common? Looks like those involved had at least two
other bridge related incidents in the past -
[http://www.miaminewtimes.com/news/fiu-bridge-collapse-
constr...](http://www.miaminewtimes.com/news/fiu-bridge-collapse-construction-
firms-accused-of-unsafe-practices-10176596)

~~~
sitharus
Not major infrastructural bridges, there's a list on Wikipedia:
[https://en.wikipedia.org/wiki/List_of_bridge_failures](https://en.wikipedia.org/wiki/List_of_bridge_failures)

The US seems to have a lot, but there are a lot of bridges in the US.
Construction is pretty risky though, there are often elements that are
incompletely supported - engineers do plan for this and ensure they are strong
enough.

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pram
It appears that the intended final design includes suspension cables, but it
looks like it was installed without them attached?

~~~
sitharus
It looks like a typical cable-stayed bridge. Often spans are installed in
advance of cables by omitting heavy elements, like the deck, so the span is
self supporting. The cables are then installed and anchored and the deck is
fitted.

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giarc
>The $14.2 million project was designed as a cable-supported bridge by MCM and
Figg Bridge Design. Figg was hired to design the replacement for a bridge on
I35 in Minnesota that collapsed in 2007 and killed 13 people.

1 paragraph later.

>“In our 40-year history, nothing like this has ever happened before,” Figg
said.

EDIT - As others have pointed out... I misread these statements.

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maxerickson
They designed the _replacement_ that was installed in 2008. The bridge that
collapsed was designed by a different company in the 1960s.

[https://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge...](https://en.wikipedia.org/wiki/I-35W_Mississippi_River_bridge#Design_and_construction)

~~~
giarc
Oh I see... I've edited my comment.

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mudil
Famous video of "Galloping Gertie" Tacoma Narrows Bridge collapse in 1940:

[https://youtu.be/j-zczJXSxnw](https://youtu.be/j-zczJXSxnw)

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gumby
People died and FIU offered...yes, thoughts and prayers (look at the end of
the article). Sigh.

