Posted on 03/16/2018 6:42:02 AM PDT by knarf
Seven ,minute, very good explanation of pre-stressed concrete
SO much is being discussed about the collapsed bridge in Florida, having worked with pre-stressed concrete, I thought it advisable to show the video orientated world just what is going on.
The principle is simple and has been used for decades.
The first thing I thought when looking at that bridge being raised into position was where are the under girding I-beams like other non-suspension bridges/overpasses.
bfl
Sounds like they used post tensioned not pre tensioned.
Years ago I ustashi see these things on flat beds going down I 95 in Fl as exits were being constructed
So was this thing being put in position with a magnet went it came down or was it in place already and then collapsed.
This was post-tensioned, both laterally and longitudinally. From the looks of it, the deck looked mighty thin, so the roof might have been part of the contributing structural system. There just doesn’t seem like that much concrete to take that much compression load for a 174 foot span without the roof being part of the structural system. I’m just a lowly engineer, so what do I know?
https://twitter.com/MoniqueOMadan/status/974478688346693632
Here is the footage showing the #fiubridge collapse. @MiamiHerald
twitter.com
Lots of our bridges have been built by FIGG who built Miami walkway bridge...watch the video...
My hubby is retired chemical engineer. I think engineers are the smartest ppl n the world. I am an artist. I supply the other side of life necessities... beauty etc.
Yep, I see a lot of post-tensioned designs in residential homes' slabs. I'm afraid that many contractors are using that design to cut back on the rebar and the concrete thickness.
This was a basically short span designed for pedestrian traffic.
I have no answers, but I am no longer the reader I used to be because of failing eyesight.
I just wanted to get the picture drawn in the thoughts of those that will comment.
The bridge was poorly made, or inappropriately cured, IMO.
knarf wrote: "...I am no longer the reader I used to be because of failing eyesight."
As one who successfully enjoyed results of RK surgery to restore 20/20 vision in '85, but now suffer from age related near-sightedness, I sympathize. Saw this report this morning and thought you might be interested:
It was preconstructed and installed in one piece last Saturday. It seems they were making adjustments to the tensioning when it collapsed.
I've had vetrectomy with a peel (NO idea what that is) on both eyes after cataract correction .... my eyes are plastic anymore.
I might not have anything to work with.
Like teeth, once you've brushed your enamel away, NO whitener can whiten a dull bone color.
From the video, it would seem then that they over tightened and a cable snapped and the rest followed.
Wonder if they were using US Steel cables and girders or foreign supplier ?
If so I think the contractors are screwed.
(Looks like MCM Construction ?)
Traffic under and across should have been stoped, detoured, whatever during any positioning or adjusting until the final support and cables were in place
Just my 2 cents
Now you're meddlin' !
/8^)
Is there anything known yet about the actual quality of the concrete itself?
The Romans knew better to wash the sand they used to purge the salt content out of the sand.
That's why to this day there are many Roman built concrete and cement structures still standing.
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