In unbonded post tension concrete flat plate slab - Multi story building, in case MEP installation were a drill used in concrete slab make a penetration in bottom more than 3/4" (the min concrete cover for PT cable) and then cut the cable, it can been seen goes out side edge slab around 3" , but the question is: if curtain wall used as facade, all edge slab will be hidden, how can I know if we have a new cut cable?
the picture shows one PT (Post tension) cable hit (drill cut it under the slab) in the middle of floor, you can see how its easy to note it,
Dear Ehab
For sure you will note if you cut a cable or even a single strand. Each 5" strand is carrying about 12 tons of force, cutting it will suddenly release all this force, you will hear high noise like blast and will feel the shock in the slab, also, the released force will through the wedges of this strand away like bullets. If the curtain wall is installed, it will be damage by those wedges.
it is not a happy experience, take care.
best regards
its has sound, but no way to hear any sound during constaraction, high noise of MEP equipment's were more loudly, also the post tension cables has profile, they ran up over columns and down at middle of spans, so immediately a high percent of forces with be observed, also due concrete patched used to fill the Anchorage which will prevent the wages of thorough out, you can see the pictures, its only 5" the length of strand going out side edges of slab, the wedges still in place.
Dear Eng. Ehab,
My answer based on personal experience, I saw it my self.
Any way, if you asking about what to do if you cut a strand, you have 2 solutions, the 1st is to over stress the rest of strands in the same duct (or adjacent ducts) to account for the lost force. the other one is to strengthen the slab with carbon fiber sheets ( or strips).
For both solutions you have to consult the designer.
best wishes
Dear eng. Ehab,
The 1st words in your question was "In unbonded post tension concrete flat plate slab" - refer to the top of the page. based on that I suggest the over stressing solution.
About CFRP solution, it is applicable even if you have MEP, CFRP strips are 10-15 cm width, you can coordinate MEP & Str. drawings to free this width even if have to do some minor adjustments.
After all this is an accident and it should not be frequently repeated. hence, you have to deal with it case by case.
again you have to consult the designer, he has all the necessary data to evaluate the proposed solutions.
by the way, I found a video showing breaking PT wire, see link below
https://www.youtube.com/watch?v=dq-agBEMLYI
best regards
well, this mean putting the strips in each lower profile, we have many, its good way to protract the cables, I believe its good idea, it will works except considering the cost.
for the link video.
Its interesting video, its pretension cables before concrete pouring, due over stressing or point damage in strand, sure, you will hear sound and its deadly area surround need safety protraction, the cables was long like 100 m length and straight, but in post tension slab its different, cables have profile with curves, the conduits which hold the strand it confined by concrete, breaking cables in side concrete slab will not go out edge slab no more like 5" for 100' cable length.
in all, I was thinking putting some censor at each face of anchorages, but its to expensive, as example: the regular PT slab with 100' X 40' contain 270 cables, this mean 135 life end, so for 30 floors:
135 X 30 = 4050 censor, its not practical solutions.
the second picture for one cut cable with 30' length, you can see its 1" out of slab edge.
thanks.
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