PT Tendon Bundles in Transfer Girders

[dengebre]

We are currently designing some long span transfer girders that require a significant amount of 1/2" unbonded tendons. We typically use rectangular tendon bundles that are six tendons wide, and this results in a large number of bundles. Is there a maximum number of tendons per bundle? Is there a minimum spacing between bundles? Thank you.

 

[KootK]

See sections C and D of page five:Link. No hard maximum on number of tendons but some limits on bundle spacing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[rapt]

Use Bonded Multistrand tendons!

 

[hokie66]

The link which KootK posted says that in practice, the limit is 6 strands/bundle. Like rapt, I don't know why you would stick with unbonded tendons...ever, but especially for transfer girders.

 

[rapt]

Hokie,

I should have expanded on this initially.

I agree, never use un-bonded tendons in transfer girders. The whole building is relying on the friction grip in the anchorages for the life of the structure.

 

[KootK]

Even in wayard north america, we'll grout our transfer beam tendons sometimes, just because the stakes are so high.

While I'm usually not one to hang my hat on this argument, we've done a lot of unbonded PT transfer beams and the track record indicates satisfactory performance. Usually a PT transfer beam will have a lot of tendons and a lot of anchorages. A friction grip failure in one isn't a big deal. A friction grip failure in several won't bring the building down and may well provide the warning that folks need to identify the problem. So, unless there's some reason to think that all of the anchors might go at once, the reliability aspect of this bothers me not at all.

Rogue corrosion issues would concern me more. I've done some main floor, perimeter PT transfer girders adjacent to traffic. Indoors... but adjacent to traffic. Hopefully the building envelope guys were up to snuff.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.