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Post tension concrete - how does it work

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Old 11-02-2007, 08:52 AM   #1
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Default Post tension concrete - how does it work

I don't understand this, unless I heard it wrong.

On a post tension concrete slab. You first run the tension cables. Pour the concrete. Let it try. Then tighten the cables.

Question. If the concrete is dried, how can you tighten the cables?

Did I get the process wrong?

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Old 11-02-2007, 08:59 AM   #2
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Default Re: Post tension concrete - how does it work (GoLowDrew)

Put the high strength cable in a tight fitting plastic sheath, like 0.065 wall thickness. Slightly tension cables so they are straight. Pour concrete. Steam cure concrete. Swage tapered ferule on one end. Let it seat into nice pocket in concrete already provided with styrofoam plug when concrete was poured. Tension cable with ratcheting hydraulic gripper/stretcher with load onto face of concrete. Swage tapered ferule on opposite end of cable. Release hydraulics, and allow cable to seat in ferule trap. cut cable. Repeat as necessary.

.... at least that is how I would do it Drew...
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Old 11-02-2007, 09:04 AM   #3
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Default Re: Post tension concrete - how does it work (GoLowDrew)

After the concrete is placed and has reached its required
strength, usually between 3000 and 3500 psi (“pounds per
square inch”), the tendons are stressed and anchored. The
tendons, like rubber bands, want to return to their original
length but are prevented from doing so by the anchorages.
The fact the tendons are kept in a permanently stressed
(elongated) state causes a compressive force to act on the
concrete. The compression that results from the posttensioning
counteracts the tensile forces created by
subsequent applied loading (cars, people, the weight of the
beam itself when the shoring is removed). This significantly
increases the load-carrying capacity of the concrete.
Since post-tensioned concrete is cast in place at the job site,
there is almost no limit to the shapes that can be formed.
Curved facades, arches and complicated slab edge layouts are
often a trademark of post-tensioned concrete structures.
Post-tensioning has been used to advantage in a number of
very aesthetically designed bridges.
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Old 11-02-2007, 09:30 AM   #4
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Default Re: Post tension concrete - how does it work (Nikos)

this sounds like my line of work, what do you guys do for a living?
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Old 11-02-2007, 09:36 AM   #5
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Default Re: Post tension concrete - how does it work (BIGBLOCKEK)

Google search analysts
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Old 11-02-2007, 09:55 AM   #6
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Default Re: Post tension concrete - how does it work (x justin)

I am a civil engineer, structural bridge engineer but I also know how to copy and paste ****
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Old 11-02-2007, 10:22 AM   #7
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Default Re: Post tension concrete - how does it work (Nikos)

I always thought that you tension the cables then pour the crete. After it dries you release the tension.

It creates more force in the concrete to hold it together better.
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Old 11-04-2007, 05:29 AM   #8
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Default Re: Post tension concrete - how does it work (thesmogman)

Yes, that is the prestress concete, he asked for POST tension
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Old 11-04-2007, 12:30 PM   #9
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Default Re: Post tension concrete - how does it work (Nikos)

Quote:
Originally Posted by Nikos
Yes, that is the prestress concete, he asked for POST tension
Yup. I'm a Civil Engineer too and thought to first google a more accurate response before posting.
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Old 11-04-2007, 12:32 PM   #10
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Default Re: Post tension concrete - how does it work (Bishop Don Shizzle)

Prestress and post tension suck because I have to have the floor surveyed before I drill big *** holes in it.
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