PT - single broken strand (of 7)

[DETstru]

I have a two-way PT slab project currently under construction. The [genius] contractors decided to core a hole through 4 tendons in a 16-tendon band.
No visible damage to the slab.

After further investigation, it turns out that only 2 of the 4 were cut all the way through. The other 2 tendons each have 1 broken strand (of the 7 strands). After some reading, I believe the friction in the tendon along its length will transmit the tension from its 7 strands to the 6 remaining strands where the 1 strand is cut.

I intend to thread 2 new tendons for the 2 that are cut though. I can get away with only 14 tendons in that band.

My question is should I leave the other 2 intact or have them cut as well? Since the tension from 7 strands is now being held in 6, that's a 17% increase in tension in each strand. That's under the ultimate strength of the strand but it doesn't feel great and I don't want to risk a future break. I also don't know how much I really trust the remaining strands. It's not inconceivable that they were damaged in some way as well.

 

[Ingenuity]

The other 2 tendons each have 1 broken strand (of the 7 strands).

I think you mean 'wire' - seven wires (6 outer and one central [and slightly larger diameter] inner/'king' wire) make up a 7-wire 'strand'.

Be very careful in visually examining the number of cut or nicked wires - it can be difficult to accurately determine how many wires are indeed damaged. Do not rely on the contractor to give you this info - best to go to site and check it out for yourself. If the depth to the cut strands is somewhat deep and/or the core hole small it can be real tough to determine the actual number of cut/nicked/damaged wires.

If it was me, and I needed 14 of 16 tendons to make the design calc out, I would inform the contractor to repair ALL damaged tendons. The additional cost to remove and replace 2 vs 4 tendons is very minimal. The building owner paid for 16 tendons - the contractor should give them such.

Are the subject tendons single-end stressed, or double-end stressed, or at a construction joint?

Also, the repair should also address the repair and reinstatement of the sheath at the core location - PTI has some recommended MINIMUM's for sheath repair. My preference is to use a HDPE injection welder (like a MIG welder for PE plastic) and splice a segment of new sheath and seam weld the new to old. If the exposure conditions are INTERIOR you may get away with PTI-approved duct tape, or similar.

PTI sheath repair FAQ: Link

Good luck!