Existing column ties cut

[ajk1]

We have found when we removed an 8 foot length of hollow sounding concrete on one face of a 40 year old existing column, that all the column ties have been cut out on that face, so that there is nothing tying the #8 corner bars of that face. In fact, at least one of the corner bars has been also cut out and we are still investigating whether the other corner bar is there or not - so far we have not found it. The column is irregularly shape, with 5 corners rather than the normal 4. We don't know if the bar removal was done at the time of original construction, although I suspect so. I suspect it was done perhaps because the bars were showing on the surface due to lack of cover.

Question: In the design of a column, is it assumed that the ties and vertical bars provide confinement to the core of the column? If that be the case, it may be difficult to check this column strength by the normal procedures. On the other hand it will not be easy to add back the ties and missing verticals) even if we build out the concrete.

 

[SrVaro]

If you have access to all four faces of the column there are products out there that can increase the capacity of the column. One is FibreWrap. I have used them to reinf a column where we were asked to "engineer" it after the contractor placed with no drawings.

 

[ajk1]

That may be a possibility, although we would have to break thru a wall into a library that is in daily use, to get the wrap all the way around. But I think we should exhaust all avenues to show that it works before doing that, and to that end I posed the question as to whether the existing column might perhaps be shown to work. Hard to believe that they cut out the bars without having the ok from an engineer to do so.

 

[jayrod12]

If you don't have proper ties then the column is NFG for any real bending resistance if required. Elsewise, without proper ties you cannot count for any contribution of the vertical steel in the axial capacity.

 

[SteelPE]

I know this is a little off subject, but who is responsible for designing the FibrWrap? Is this something the mfr does with information provided by the EOR or is this something the EOR needs to do?

 

[steellion]

My (relatively limited) experience with carbon-fiber reinforcement is that is a proprietary, delegated design. The EOR provides the criteria to be met, and the specialty engineer would design the carbon-fiber reinforcement accordingly. In this case, I would probably indicate that carbon-fiber reinforcement shall be provided for confinement.

 

[JAE]

Another option that doesn't include fiberwrap is to install horizontal steel straps around the perimeter.

What you do is fabricate steel bands - perhaps 3/8" thick x 3" wide - around the column where the ties originally were intended to go.

The straps would be carefully fabricated to be just a bit short on each face. The contractor can flame heat these straps to expand slightly and
then install on the column. The ends of the straps are either bolted or welded together. As it cools it tightens on the column.

For the vertical bars, it might be best to chip away at the concrete cover and expose the bars such that you can supplement the vertical bars with new bars.
These might have to lap the existing bars or be welded onto them. Even if they aren't A706 weldable bars, you might be able to figure out the chemistry to get a good weld.

For a single cut bar, use two adjacent bars to keep the steel-bar configuration symmetrical.



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