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Post Tension Slab Project
This thread has 17 replies. Displaying posts 1 through 15.
Post 1 made on Saturday May 24, 2014 at 15:14
SB Smarthomes
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I've been working on a significant residential remodel where the main level floor is post tension slab with traditional frame construction and the lower level is all concrete.

Between electrical, plumbing & HVAC there have been several hundred cores drilled ranging from 2"-16" in diameter.

They found where a core was drilled through the post tension floor for a drain back during original construction and one of the cables was hit.  Didn't cause catastrophic damage, but did blow out some of the surrounding concrete when it gave way.

I've heard bad stories about cut cables doing lots of damage, but I expect this is on larger structures like multi-story commercial buildings, bridges, etc.

Here's a couple photos... you can see the cut cable splayed out on the right side.





 
www.sbsmarthomes.com
Santa Barbara Smarthomes
Post 2 made on Saturday May 24, 2014 at 16:42
Ernie Gilman
Yes, That Ernie!
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PTkills. Everyone was very lucky.

From [Link: posttensioncablelocators.com]:

The cables installed are usually pulled so they each have approximately 28,500 lbs. of tension. The released tension will find the path of least resistance. A very loud noise similar to thunder usually occurs if the cables are cut while coring or saw cutting a slab. Experienced saw cutters will know immediately something has happened. Many factors can influence what will actually occur. Some cables just retract back into the slab towards the perimeters of the home. Some cables retract and protrude out of the slab on the side of the house. These types of cable cuts are relatively easy to repair.

Other times the cables pop up above the concrete in several places in a sort of ripple effect along a line towards the perimeter of the home. This obviously destroys the concrete and flooring and can be quite expensive to repair. Injury can occur if someone is standing on top of the cable when it releases.

The main reason to use our services is to avoid the worst case situation when a length of cable whips out of the slab and injures someone. This is a very serious situation, of course. We think it would be negligent for a contractor to cut into a slab suspected of having cables without having them located. Don’t take a chance. Just call us, or some of our friends in the industry.

That was 28,500 pounds of tension.

Researching this answer, I read of a worker 35 feet away from the fixed end of the cable.  As the cable was being tensioned it snapped, flew back toward the fixed end, flew 35 feet past it, nailed this guy "in the clavicle," and killed him.  A search of "pot tension accident" gives lots of responses, none of which are the first such story I heard, of a cable being cut and snapping some fifty feet outside the building, killing someone.  But 35 feet is a damn big expansion of the danger area!
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
OP | Post 3 made on Saturday May 24, 2014 at 17:17
SB Smarthomes
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I didn't want to imply that drilling in post tension slab wasn't dangerous or that you shouldn't take proper precautions.

Seems like this subject comes up a couple times a year on the forums so thought I'd post about the experience.

 
www.sbsmarthomes.com
Santa Barbara Smarthomes
Post 4 made on Saturday May 24, 2014 at 18:21
Trunk-Slammer -Supreme
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On May 24, 2014 at 16:42, Ernie Gilman said...
| A search of "pot tension accident" gives lots of responses!



I'm guessing that "pot tension" is what occurs when someone Bogart's a joint.



That can be VERY dangerous... :-)
Post 5 made on Saturday May 24, 2014 at 19:13
radiorhea
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Lol
Drinking upstream from the herd since 1960
Post 6 made on Sunday May 25, 2014 at 10:21
Ernie Gilman
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I'm going to have to start saying I'm doing those typos on porpoise.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 7 made on Monday May 26, 2014 at 02:48
Mario
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I go 4x4 and when people have to use a winch, most still use steel cable.
I've seen first hand the damage that a snapped winch cable can cause and it ain't pretty.
Post 8 made on Monday May 26, 2014 at 10:31
Hi-FiGuy
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Did some research on Post Tension Slabs, scared the poop out of myself

I had no idea they are so prevalent in the construction of homes in So Cal.

Is that something that has to be disclosed at time of purchase?

How do you identify PTS by looking since the edges of the slab would be below grade.

Seems like a risk to reward percentages don't add up.
Post 9 made on Monday May 26, 2014 at 13:41
tweeterguy
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On May 26, 2014 at 10:31, Hi-FiGuy said...
How do you identify PTS by looking since the edges of the slab would be below grade.

We have a lot of post tension slabs in Las Vegas too. The ones I've seen (including one of my homes) had a stamp in the garage floor noting its presence. I had initially planned for a rack bolted to the concrete in the home (entire first floor was stained concrete) but chose not to due to the fear of destroying the place or killing someone.
Post 10 made on Monday May 26, 2014 at 17:32
Hi-FiGuy
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Cant believe that stuff is legal, I could not sleep at night on a multitude of levels knowing my children are sleeping on top of it..
I have never heard of rebar exploding out of a floor and killing somebody.
Post 11 made on Monday May 26, 2014 at 19:53
Ranger Home
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Im going to remove the gas from my house! I read about an explosion that killed people! crazy huh? get rid of your gas lines.

Im going to never get on a jet plane. I read one crashed! And there were kids on board!

Saw a video of a bridge collapse. Im NEVER crossing one again!

PTS are prevalent on grounds that are no that solid and are prone to shifting. Its a HUGE plus on stability. If one house for sale had it and one didnt, you would want the one WITH it. I have never seen nor heard of PTS exploding or breaking or causing ANY problem EVER. The dangers are doing the installation and even then its very rare and less than lighting strike deaths.

Hifi, youre over reacting lol.
Post 12 made on Tuesday May 27, 2014 at 00:19
Ernie Gilman
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Right. If PTS was dangerous without someone messing with it, we'd have heard A LOT about its problems way before now!

I understood that my installation could cause damage, but not until researching for this thread did I realize that the PTS installation itself could kill someone. Makes sense but I guess my brain didn't want to go there.

I understand that there's some minimum distance the cables have to be below the surface, and you can drill for redheads and such above that. But who'd risk it? In the cases I've seen lately, the slab was xrayed and marked so cores and redheads could be placed safely.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 13 made on Tuesday May 27, 2014 at 01:38
Hi-FiGuy
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I don't live and sleep or lay on the couch and watch TV on a bridge, or a plane for that matter.

I realize I am over reacting, or not, but there are odds here, and I understand the benefits.

I have never considered it being used in residential and I have drilled into a slab or two in the past.

In the future I will investigate before drilling.

Still that is a lot of stored energy to be sitting on.
Post 14 made on Tuesday May 27, 2014 at 01:41
Hi-FiGuy
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On May 26, 2014 at 13:41, tweeterguy said...
We have a lot of post tension slabs in Las Vegas too. The ones I've seen (including one of my homes) had a stamp in the garage floor noting its presence. I had initially planned for a rack bolted to the concrete in the home (entire first floor was stained concrete) but chose not to due to the fear of destroying the place or killing someone.

Was the stamp out in the middle of the garage floor or neatly tucked away in a corner where someone could put a cabinet on top of it.
Post 15 made on Tuesday May 27, 2014 at 11:29
BlackWire Designs
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On May 27, 2014 at 01:41, Hi-FiGuy said...
Was the stamp out in the middle of the garage floor or neatly tucked away in a corner where someone could put a cabinet on top of it.

Mine is at the center of the entrance right at the big garage door
BlackWire Designs
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