Concrete Column Detailing 1

[papaaj]

Here is an issue which probably very basic and simple, yet has engineers in my office perplexed.

ACI 318, Section 7.10.5.4 requires that ties in concrete columns be provided "not more than one-half a tie spacing below the lowest horizontal reinforcement in slab or drop panel above." Section 7.10.5.5 states that when beams frame into a column on 4 sides, the ties may be stopped 3" below the lowest horizontal reinforcement in the shallowest of the beams. My interpretation of these requirements is as follows:

If I have a 12" slab supported by 24" wide by 36" deep (incl slab thickness) beams framing into a 24" square column on 3 sides, the ties in the column will need to extend up into the beam, to 1/2 a tie spacing below the bottom reinf in the slab. This would be the case irrespective of the seismic requirements for this column, but in my situation, there is no need for seismic considerations (i.e., column is not part of seismic-load-resisting frame).

Is this a correct interpretation? I have never seen a column detailed in such a manner - usually the ties are stopped below the beam, regardless of the number of beams framing into the column. It seems that to run the ties up into the joint between the beams and column would result in so much reinforcing that it would be difficult to place all the reinf, let alone cast the concrete. However, it seems that the requirements of Section 7.10.5.4 apply to ALL columns.

I would appreciate any comments on this code requirement.

Thank you,

Tony

 

[Qshake]

In my assessment your interpretation for this case is correct. Further to this point, see Notes on ACI 318-99 which depicts your situation.

The behavior or performance you are after is to confine the core of the column and when the horizontal beams are not present on one or more sides this is accomplished with the ties.

In your case, this may be more problematic than the benefit derived but it is good detailing based on lessons learned. In my experience, it takes a good rodbender foreman to figure out how to place that reinforcing but it can be done. And it is prudent to have inspectors make sure that it is done a detailed.