Concrete Column Splice

[lutein]

Have you ever seen a concrete column splice @ slab (between floors) being connected by only 1 dowel? In other words, assuming that the slab-column connection is pinned in analysis/design, have you ever detailed such pinned condition by just placing 1 vert. dowel that connects the column above to the column below?

I happened to see this detail, and it seems correct theoretically since it's a pinned connection, there is no tensile splice required; however, I don't know if there is problem by doing this. If this works, it will be a great saving in steel (especially with the steel price rocket high these days)

I would appreciate input and discussion to shed some lights on this idea.

Thank you

 

[kieran1]

would this not greatly reduce the rebustness of the structure

Kieran

 

[rowe]

with regard to "robustness?", if you design the column as pinned, then diagonals or walls are usually designed to resist lateral loads, and hopefully, the structure is adequate to sustain the anticipated loads.

With regard to redundancy, I would suggest that one rebar dowel is not adequate. The crossed rebar detail is far better.

 

[SRO]

Am I wrong to assume that this one piece is only at the slab, and there is full "typical" reinforcing through out the rest of the column?

 

[jike]

Do not the main vertical reinforcing bars need to be fully developed at the floor line? How are you accomplishing this development without the lap of the bars below?

 

[lutein]

Thanks for the reply.
The answer to Jike's question is:
No, the column vert. will be stopped w/ 90deg hook below the slab. Only 1 dowel penetrate through the slab into the column above. In the design of the slab, the column support below is assumed to be pinned. and all lateral loads are to be resisted by shear walls.

 

[jike]

Do you also have 90 degree hooks in the column verticals just above the slab for the upper column development? Do these hooks make it difficult to get concrete completely in the column without segregation or voids?

Can whatever (compressive or tensile) stresses you may have be carried by the plain concrete column beyond where the verticals terminate in a hook? Wouldn't this short unreinforced section severely limit the capacity of your column?

With hooks at both ends of each lift of columns, isn't it more cost effective and practical to just extend the bars up from below and lap as is the traditional way of constructing columns?

 

[denoid]

We've never used a single bar dowel for a pinned connection, but have used minimal reinforcing to create one, (for example 4-#4 bars approximately 3" clear each way near the center of the column). Usually, we've done this only at the footing to concrete column connection, and just lap-spliced the columns for all floors above that, assuming that the column would crack for moment release.

 

[J1D]

Lutain,
I agree with Jike.
Why do you have to make a physical pin at the slab-to-column interface. Once you have the shear wall for lateral support, the momemt at the interface is very small regardless of the rigidity of the interface. I'd recommend extending vertical rebar through the slab (assume you don't have over-reinforcement)to save your concerns and justification. This kind of saving is nothing.
Regards

 

[cap4000]

J1D and Jike

I am with you guys totally. I always design my concrete columnns with a min. 10% or 0.1t in each direction as a Min. Eccentricity Requirement per ACI Code. Those bars must be developed from one column to above and below. Overall cost savings can't be that much anyway. Also, please keep in mind the P-delta magnification effects from sway or drifting of your shear walls. Lutain reconsider, as you say in "theory" is not recognized as actual real world job site conditions. Good Luck.