CIP Concrete Column Splice 1

[Eldorado]

My typical concrete column detail shows the main bars for the "lower" level column with a sweep in them as they pass through the beam above and extending as dowels for the columns at the level above. I have a contractor that ordered straight bars that stop below the bottom of the beam. He wants to use dowels that extend into the low column, through the beam and into the high column. I have never used this type of a detail. Any insight as to experience with this situation or design concerns would be appreciated.

 

[JAE]

As long as you provide the required number of bars and splice length you should be OK. It seems like this would take more effort to cut, tie and locate these bars in the field.

The other issue is that with the splices, your "dowels" would be set inside the main column bars and thus, at the floor level your "d" of your column would be smaller than the typical "d" of your columns beyond the splice.

This usually occurs anyway with 1:6 tapered column bars extending up through the floor depth and lapping with upper column rebar just above the floor.

We usually avoid this by moving the laps up into the mid-height of the column (see this discussion: thread507-298261)

 

[TXStructural]

The proposed detail should be acceptable, subject to your evaluation of strength and structural integrity. If the bars are spaced sufficiently, dowels should be just inside the ties, adjacent to, but not inside, the main bars. They have to be fastened well, and using longitudinal steel and ties makes this more secure. Also, you are still subject to spacing, congestion, and maximum reinforcement ratios in the lap zone. Reinforcement without properly consolidated concrete all the way around doesn't function well. (We see this on the west coast from time to time.)

Starting lap splices at the top of slab is the economical way. This allows the upper cage to be set directly on the concrete surface. Starting splices mid-height required some way of securing the upper cage in place before forming. Tie wire is not really made for this kind of stress, and falling rebar cages are dangerous. If you use mechanical splices, splice them at a height above the slab to give workers good access. The offset bends in the longitudinal bars should start inside the floor beams/slab and be complete at the top of slab.

 

[JAE]

TXStructural - I perhaps mis-spoke - flipping the splice still allows for the upper cage to be set on the floor. It just reverses the 1:6 taper from occurring inside the beam-column joint area to being located above the floor at the splice length height. So "mid-height" was not a correct description.

See attached sketch

 

[Eldorado]

Thanks JAE, Yes, logically I could not see a reason why the straight bar dowels would make a difference. Depth, area of steel, everything seemed to still add up, but I have never used this type of column splice and wanted to post for comments. I have had to use mid-height laps in the past because sweeps were left out, but the concrete subs in my area really seem to struggled with it.

 

[Eldorado]

TXStructural,

My columns are square. Are you suggesting that Config A is better than Config B on the attached sketch?

Thanks.

 

[JAE]

In terms of average effective depth, d, the two options are similar.

 

[TXStructural]

They are essentially equal, but option A will generally be easier to tie securely, if bar spacing permits. The attached page from the CRSI Placing Reinforcing Bars publication is shown in the section on connecting from foundation to column.

As for reversing the usual scheme and putting the offset on the upper cage, it is perfectly acceptable as long it is detailed sufficiently in the CD's. That said, since it is non-standard, I recommend that you discuss it with the contractor to be sure it gets done correctly. Things done in a non-standard way are more likely to get built wrong.

 

[asixth]

I would do it but I do many things that some people wouldn't agree with. If column bars are cranked than I provide extra ties at the crack for any popping forces that may occur. I don't crank anymore than 1:6 and provide ties at 1/2 centres over lapped splices in columns.

 

[MrHershey]

Might also be a good idea to get in touch with the special inspector if you can to try and touch base and voice concerns to make sure it's built correctly. Always love working with good special inspectors who can essentially be my eyes and ears out in the field and keep an eye out for the little details that I'm prone to miss on site visits.

Unfortunately all too often special inspection just goes to the lowest bid who then progresses to not keep the engineer in the loop on anything. If they even show up at all.