Lap Splice vs. Bundled Bars

[engrjenjen]

Is there a proof that the concrete will identify whether the longitudinal bars are bundled or lap spliced only? I encounter this mostly when detailing columns and walls.
How about if the length of splice exceeds what is required, is this considered bundled?

 

[Retrograde]

I would say it is not considered bundled if you are not relying on the strength of both bars.

 

[engrjenjen]

I have an example here, please refer to detail shown.

At section A, the column requires 20-28∅ bars, 10 of those were lap spliced. As per ductility requirement, area of reinforcement over gross concrete area should not exceed 6%. Is it correct that at this section:

ratio = (20*615)*100/(500*1000) = 2.46%

instead of:

ratio = (30*615)*100/(500*1000) = 3.69%?

I considered only 20 bars since I am not relying on the strength of both bars. It is assumed that the bars with lap splices are continuous bars.

 

[KootK]

For ductility and strength, you've got 20 bars.

For local congestion, you've got 30 bars.

A lap is most definitely not a bundle.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

I think the OP may be confusing "bundled" and "continuous". The words mean entirely different things.

 

[engrjenjen]

Hi hokie66,
We cannot compare "bundled" with "continuous" as you've said the two are different things. What I mean with "It is assumed that the bars with lap splices are continuous bars." is that at section A (as previously shown) there are 10 bars which have lap splices, and counting the bars shown on that section it gives 30-28∅.
Based on my understanding on earlier post, lap splice is just a connection of (two) continuous bars, that's why I only considered 20 bars when computing for the ratio.

Hi KootK,
Thank you for the clarification.
Actually what we usually do at work is that we check all the sections with lap splices and then consider all the number of bars (shown when cutting a section) when computing for the ratio. I'm just curious with the method that we use.

 

[TXStructural]

There is no restriction about maximum reinforcement ratio due to laps. The limits are practical, for construction purposes. In the section shown, it seems that you are lapping top and bottom bars in the same section. While I do advocate for laps at 1/4 or 1/3 points, the practice is not widely used. It also looks like you are staggering laps, another good practice that is not used as often.

 

[KootK]

While I do advocate for laps at 1/4 or 1/3 points

What is the benefit of doing this? Just to move the lap away from the peak moment a bit? I would think it a major inconvenience for upper cages not to be able to simply rest on the concrete.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

TX,
We were talking about columns, I think.

 

[engrjenjen]

TXStructural,

I'm referring to a column here.

 

[TXStructural]

I should have read more carefully. And that makes clear Koot's remark - yes, that would be troublesome.