PT Cable cleat loose

[seminole22]

We have exposed a P.T. slab edge which, after the mortar plug fell out, revealed a single location where the 2-piece cleat is not recessed with in the socket and is loose enough to be moved by finger pressure. (it appears that it was never tensioned, but the cable end was cut.) The question is what to do now. The building has performed for 7-years in this condition. I believe tensioning the strand would require splicing a new cable at a port cut away from the slab edge so that we could have enough cable length to grab onto at the edge. Any suggestions as to approach? experience or hints on this repair?

 

[dik]

First, might be OK to review the numbers and see how close the limit load capacity is. There's often some redundancy.

If it is essential that remedial work be undertaken, it might be difficult splicing to retension. Can you cut out the slab in the vicinity of the first point of inflection and stress from that location? Even if not required, I often have taken the strand centroid to the top kern pt of the slab to induce a little -ve moment resistance at that location and to improve the drape.

dik

 

[DTGT2002]

Have you contacted the PT supplier for help, or had the contractor call for assistance? There are special rams available that can grab a very short length of cable . With the ends cut, I doubt it is a good possibility, but it is worth persuing as no change to the design would be ideal.

I'd second reviewing the numbers, if the strand cannot be tensioned without great effort. What is the purpose of the cable, is it primanry reinforcement or a temperature tendon?

I would also ask the PT supplier about the possibility of threading a new cable through the in place jacket, assuming it is unbonded PT.

Good luck!

Daniel

 

[Ingenuity]

seminole22,

It may be worth invsestigating if the reason for the anchorage grout pocket falling-out was due to the strand rupturing internally due to coring/drilling or possibly corrosion. Tendons occasionally do go unstressed, but with the grout pocket falling-out it may be explained by other reasons.

ACI 318 section 18 has the 2% rule that states that "total loss of prestress due to unreplaced broken tendons shall not exceed 2% of the total prestress". You can argue what is the total prestress requirement is: full slab panel width, banded tendon prestress etc.

If it is deemed that retensioning is necessary you have a few options:

1. Use special ram/equipment to grip remaining strand tail. This can be problematic if the strand tails were cut very short and with slag from the cutting torch.

2. Access the strand internally via a partial depth invasive probe at least 3' from the anchorage and install a splice chuck and new partial-length segment of strand from this splice chuck to the existing anchorage (should be able to hand push in 4 or 5 feet of strand with little problems). Splice the new-to-existing strand with splice chuck. Re-stress the tendon from the existing anchorage. Patch back the probe. Patch back the anchorage pocket. The probe dimension and the location of the splice chuck will have to accomodate the expected strand elongation for the given tendon length to avoid 'binding up' the chuck during stressing. Of the adjacent tendons are in close contact to this untensioned tendon, you may have to increase the length of the probe to enable the chuck to be installed.

3. Relocate the existing anchorage by approx 4" to 6" from the existing slab edge anchorage location and replace with new. This will enable you to have more stressing tail where by the strand can be gripped and re-stressed without having to splice in a new partial-length segment of strand and splice etc. This option will not work is there are close adjacent anchorages that will not permit concrete chipping in such close proximity to stressed tendons.

4. Full length strand removal and replacement - will be expensive and possobly unnecessary.

Best to contact a PT repair contractor in your area who will be familar with the above techniques.

Good luck.