Cut post tensioned strands
Cut post tensioned strands
(OP)
I have a situation where a plumbing contractor sawcut an existing warehouse slab that he later learned was a post tensioned slab. The building is 350' X 80' with grade beams and caissons at 25' bays in the long direction and 26'8" bays in the short direction. The cut extends diagonally across an interior bay. The contractor is proposing cutting the tendons, adding a couple at the cut ends and then re-tensioning the tendons. Then replacing the slab. Is there an issue with retensioning the tendons before replaceing the 5 foot strip of concrete removed to find the ends? I am thining we at lease need to pour strips between the tendons to take the compressive force from the tensioning. I am also planning on doweling in repar at the edge of the patched area to transfer the shear from the new to existing slab. Has anyone dealt with a repair like this. Is there a typical way this repair is done for a full bay length?






RE: Cut post tensioned strands
RE: Cut post tensioned strands
I agre, bring the specialists in. Call your local PT contractor and see if they can point you in the right direction.
RE: Cut post tensioned strands
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Cut post tensioned strands
RE: Cut post tensioned strands
You have been in Australia too long!!
RE: Cut post tensioned strands
made me laugh and think of my original home.
The whole unbonded PT thing is too entrenched in some countries to change.
I always have the image of an unbonded tendon launching out through the end anchor if cut, suspect that is not really the case though.
RE: Cut post tensioned strands
The tendons won't go shooting out very far, but the wedges could.
During demo of a elevated un-bonded PT slab, we had them set up plywood baracades in front of the anchorage points. As the tendons were cut, the wedges would dent up the plywood pretty good- but none penetrated it.
RE: Cut post tensioned strands
you could be right, but the sentance about the contractor already cutting the slab would make for a fun day.
ANY FOOL CAN DESIGN A STRUCTURE. IT TAKES AN ENGINEER TO DESIGN A CONNECTION."
RE: Cut post tensioned strands
Most engineers specified bonded tendons after this event.
RE: Cut post tensioned strands
Too bad the engineers in the other 51 states didn't listen. The post-tensioning world would now be a beter place if they had! Then, Alaska is never really considered to be part of USA except when they calculate their locally sourced oil quantities is it!!
Wonder how all the West Coast unbonded PT buildings are going to fare when the big one hits!
RE: Cut post tensioned strands
RE: Cut post tensioned strands
So have the tendons been cut yet or not? Your opening post is somewhat confusing. If the plumbing contractor has already cut through the tendons repair is the next step.
If the tendons have not been cut yet than I suggest that you have the slab scanned with ground penetrating radar. You may find that the tendons are bundled and you can avoid cutting them altogether. This may mean that some modifications will need to be made to the plumbing chase but this would be preferred to making structural repairs.
I just finished detailing shear transfer across a pt slab and it is not pretty or cheap and I would definitely avoid it if possible.
RE: Cut post tensioned strands
Yes, you will need to replace the cut out concrete to take the compression along the cut. You will have small leave-outs where the tendons will be repaired. The space required to make the repair connections is relatively small, and they will use "dog-bone" connections. The repair contractor should be experienced and they will have to verify the end anchorages.
It is not all that much trouble when it is a single tendon that is damaged, but this isn't quite as simple.
If they are unbonded, I expect that the anchorages have been unseated. I would also expect to be tendon snaking out of the slab on top or bottom, where the force cracked the tendon from the slab.
RE: Cut post tensioned strands
RE: Cut post tensioned strands
Strands are in both directions.
No cracks in the slab anwhere.
The building owner hired a scanning company to locate the tendons in the slab.
As far as we can tell they cut 25 or so tendons and all the top reinforing in one grade beam.
Quite a mistake by the cutter.
RE: Cut post tensioned strands
RE: Cut post tensioned strands
RE: Cut post tensioned strands
RE: Cut post tensioned strands
This really is not a post tensioned slab on ground but a structural post tensioned slab supported on grade beams which are supported by caissons.
The project is in the north east where this type of construction is cost effective for poor soild situations when there is a high live load(250psf)on the slab.
Thanks TXStructural for your post. This is the sort of information I was looking for. Has anyone else seen repairs done in the manner TXStructural mentioned?