Post tensioned slab on grade remodel
Post tensioned slab on grade remodel
(OP)
I am doing remodel where is post tensioned slab on grade.
I need to add some square spread footings below to support new columns. How can i get thru the slab? Can I cut the tendons? How would I retrofit them if i cut them?
Thanks.
I need to add some square spread footings below to support new columns. How can i get thru the slab? Can I cut the tendons? How would I retrofit them if i cut them?
Thanks.





RE: Post tensioned slab on grade remodel
Are the tendons bonded or unbonded?
Is this a PT Matt footing? If it is a matt footing, I would try to keep the loads as similar to the original as possible.
Mike McCann
MMC Engineering
RE: Post tensioned slab on grade remodel
The contractor cutted one tendon when he was cutting the slab for new square ftg.
RE: Post tensioned slab on grade remodel
If so, I would look at the geo tech report as there may be a bearing, excessive settlement problem with the subgrade in the PT area. In other words, more settlement possible in the area of the PT than the non PT slab.
If not, then I guess I am all wet here...
Mike McCann
MMC Engineering
RE: Post tensioned slab on grade remodel
RE: Post tensioned slab on grade remodel
Mike McCann
MMC Engineering
RE: Post tensioned slab on grade remodel
RE: Post tensioned slab on grade remodel
RE: Post tensioned slab on grade remodel
If you have only cut one strand, as long as you are careful not do damage any more, I would tend to just leave it.
RE: Post tensioned slab on grade remodel
I have repaired many severed unbonded tendons INTERNALLY without accessing the existing end anchorages, but best to check with a local PT contractor in your area to see if they have the experience to do such repairs.
Or, if the tendon is not excessively long, use a "GRABB-IT" combination splice chuck (see www.precisionpt.com) that incorporates a turn-buckle thread-arrangement that enables the strand to be re-stressed using a calibrated wrench but these are a pain to use.
The problem with both of the above stressing/splicing combination options is that the stressing hardware is bulky and for thin slabs it is difficult to accommodate, and also provide long-term durability to the hardware whilst also maintaining unbonded construction. Often the re-stressing hardware is cast-in and therefore the hardware becomes "bonded" - which I personally think is a benefit.
RE: Post tensioned slab on grade remodel
Judging by the photo, it looks like the tendon depth at the cut location is very near the bottom of the slab. This makes splicing/stressing at this location near impossible to accommodate the necessary hardware. If the tendon depth varies along its length it may be possible to accommodate the hardware where the tendon is closer to mid-depth of slab on either side of the cut, and therefore replace a segment of strand too, to 'link' the splice chuck to the center-stressing anchorage.
RE: Post tensioned slab on grade remodel
Does anybody know how can i set the prestressing load into the splicer if i don't know what was the stress before?
Thanks.
RE: Post tensioned slab on grade remodel
And there is no way to check the original ends of the strands.
Any thoughts?
RE: Post tensioned slab on grade remodel
RE: Post tensioned slab on grade remodel
When an UNBONDED tendon is cut the sudden release of energy does send a shock load to the end anchorages and there is always a possibility that the anchorage wedges may be dislodged. Is is more probable that the wedges will NOT be displaced.
As far as what would be the re-stressing load to place back into a cut strand, you simply re-stress to NOT exceed 80% of MUTS, and you could elect to re-stress to say only 65-70% based upon the fact that long-term PT losses have taken place, so adjacent strands are probably at a prestress level of 65%.
Anyway, I would do what HOKIE66 stated. And very quick and inexpensive
RE: Post tensioned slab on grade remodel