Post Tension Cable failure

I got an emergency call from the Fire Department about a loud explosion in a 3 story condominium. I arrived within minutes and was led to a corner unit on the 2nd floor. Once inside I observed a hole in the ceiling about 5 inches in diameter and 1 inch deep. There was concrete all over the floor and in the hole was 1 strand of a post tension cable that had shot out of the slab and left a loop about 9 inches long. This building is 28 years old and I inspected all units above below and on the same floor. There was no damage anywhere. No one had done any work that day or recently. 2 Structural engineers inspected along with me and the consensus was the same. We have never seen anything like this. For 1 strand to suddenly shoot out of the slab. The explosion could be heard over 300 yards away. Any ideas on what happened here ?

Anchor, wedge or tendon failure, not a whole lot left to go wrong, may be due to corrosion.

The Pope will likely chime in.

I’d like to see your photos!

I just closed the entry door and had one go on a vacant house.
Dust clouds for what seemed like days and hearing was buzzed for hours.
Scared the b-jeezuz out of me and was a shorts check time moment.
Didn’t get to complete the inspection because the client was with me and walked…no doubt. He said, “Could you imagine if me, my wife or kids were in that room?” I completely understood.

Barry, would you elaborate? We don’t have many post-tensioned slabs here and I’d like to learn more about them.

What are anchors, wedges and tendons and how do they fail?

What exactly happened in the home to create the dust cloud, noise, etc.? If a cable fails, is there a life-threatening explosion?

Get past the music 1 minute and watch this lecture and further episodes

This may be simpler once you know the components

The cable may still be live if only one strand has broken. The cable should be de-tensioned (which can be very dangerous) and removed.

Cable failures can be as uneventful as a “pop,” or as catastrophic as “exploding concrete,” capable of severe damage and bodily injury. If the cable is still live, the potential for further events is pretty high.

Other than drilling or cutting the stressed concrete, the cause of a cable failure can be any number of things, but generally occurs from a tendon that has been damaged prior to, or during placement. A damaged tendon is like a ticking time-bomb. . .

Here are some pictures of the “muscle and teeth” of PT cables.

The pictures show a “triple wedge” (doubles are most common in residential PT), a double wedge that is in place prior to stressing the tendon and the hydraulic ram used to stress the cable.

The last picture shows a “multi-cable” system, used in bridge construction. I worked with all of these systems for many years. . .





Here are a couple of elevated-deck pictures. . .



Thanks for all the posts. The real question here is why after 28 years ? I’ll post a picture as soon as I get to the office. My other question is now that 1 strand has “popped” will the others follow ?

Most likely this will be an isolated event. It’s very unlikely that additional cable failures will follow.

If it were to continue, the original installation methods would be suspect. The only “fix” for that would be to condemn the building.

Seems to me it would require an extremely large condom.

LOL, that leaves quite a picture in my mind…:lol:

:mrgreen: :wink:

As an ex-post tensioned concrete ICC special inspector, I want to agree with and support EVERYTHING that Jeff has said and provided. I would add that although it IS probably an isolated event due to damaged materials, I feel the engineers that were on site should contact the architect or engineer of record for the construction and get the special inspector documentation. The tendons cannot be pulled withou a special inspector documenting al the vital information. (LBS of tension, distance of pull etc) This could revel a possible installation problem though this is unlikely but no stone should be unturned when it comes to public safety. As jeff stated, if there are true issues condemnation is the only real cure.