Concrete Column Splice Repair

[Galambos]

I am currently investigating an option to repair concrete columns, which would adjust the Class A lap splices to Class B lap splices, so that the columns can take direct tension, as a result of net uplift.

I was curious if anyone has had any experience with this. My thoughts were to either splice the lower bar to upper bar with a mechanical connector or to splice additional length onto the lower bar and extend the lap length. Offset bars may complicate the mechanical coupler option.

I am also concerned about how the re-concreting operations might work. The columns are supporting a PT slab and I am very concerned about movement that might arise from concrete consolidation, shrinkage and jacking operations.

If you have any insight, I'd appreciate it.

 

[ron9876]

You cold gunite a reinforced jacket around the column which is attached to the existing column.

 

[TXStructural]

Mechanical couplers might work very well for this, with minimal problems. With ties and such in the way, getting longer bars inside the column may be a real problem. You could also have the bars welded, depending on the grade and specification. Adhere to AWS on the welding; A706 can be welded, but A615 must be preheated, etc.

As for concrete, a form and pump could work with the right admixtures and the right contractor. Avoid excessive water in the repair mix to reduce shrinkage issues. Get with a local Sika or Ciba rep and the contractor to be sure the right material gets used properly. And when a contractor says "oh, yeah, I can do that" don't believe him, and require the material supplier to be present for the prep and pump operations. (I have experience with this.)

Another problem may be finding a way to jack the floor(s) above, since an elevated slab below will not have sufficient shear capacity to hold that kind of load. It will have been designed for just what it needs, and not for everything above.

 

[Galambos]

TXStructural, that's very good advice. Are you suggesting using one mix from the floor to the underside of the existing column? or are you thinking of new normal weight concrete up to the existing concrete with a gap to be filled in with grout?

 

[rowingengineer]

sounds like a lot of work to me, have you considered using FRP to get the extra strength?

An expert is a man who has made all the mistakes which can be made in a very narrow field

 

[TXStructural]

Depending on how much repair-crete you need, you could do as you mention, but you could plan to form and pump the entire repair with a normal pump mix fortified with high range water reducer, viscosity admixture, and maybe shrinkage-reducing admixture.

The ready-mix and admix rep (from Euclid, Sika, BASF, etc.) can advise you on how to get it to pump properly, consolidate without much, if any, internal vibration, and reduce the risks of segregation, incomplete filling, and drying shrinkage.

If the lift will be fairly high and the volume of concrete warrants it, you might do it in two stages, one with forms which are open to the top; just pump and vibrate, leaving a rough top to accept the final segment. Then form and pump a layer to span the gap between new below and old above. Usually, the added cost of mobilizing the pump twice makes doing it in one run more economical.