column splice for 16 to 24 rebars

[khinz]

I know splice for column rebars is at midspan of columns.. but how do you distribute them so they won't be at one layer or location for a small 400x500mm 16 to 24 rebar column? any papers or guidelines about this in the net for comparisons? thanks.

 

[dik]

You have to be careful that you don't exceed the max % of rfg at your cross-section... Depending on bar size, you may have a lot of rfg.

Dik

 

[asixth]

As soon as you start getting up to and over 4% reo (8% at splices) then placement starts to become an issue.

The scheduler will need to crank the bars at then it's up to the site guys to place them properly. You can specify a high slump mix which should help to prevent any honeycombing during placement.

 

[hokie66]

You may have reasons, but why are you splicing the bars at midheight?

 

[khinz]

Midheight is the only place one can slice bars in a column. But for 12 bars and splicing them to add another floor (because the existing bars are short), the percentage of steel at midheight reaches 4% already. I'm imagining all the bars at midheight are double because it is only there that splices can be made (you can't splice near floor level). Is this how you really splice them? (as long as the midheight is or near 4% it is ok if the bars are doubled)?

 

[msquared48]

For the larger bars, if you use Cadwelds and stagger the splices, congestion will be minimized and you will not go over the 4% figure either, let alone 8%.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[TXStructural]

By convention, we generally splice column bars where the upper bars rest on the completed slab. It has been done this way for safety and productivity for decades. A have not seen lap spliced columns done at midheight on any project.

You say "16 or 24 bar columns". That sounds like an excessive number of bars. In a 500mm square column with standard cover and ties, 16 bars means bars are spaced at less than 4" (100mm) apart. The use of many small diameter bars might shorten splices, but where you don't need closely-spaced bars for confinement in high seismic applications, you should use fewer bars of larger diameter. Doing this facilitates placing and eliminates excessive ties.

 

[hokie66]

I really do splice bars just above the floor, and that is the typical way of doing it. Is this requirement to splice bars midheight a seismic provision in your code? If so, which code? Why do you have so much reinforcement? If for axial capacity, it is generally much more economical to use higher strength concrete than to use a lot of steel.

 

[steellion]

The ACI code limit for column reinforcement is 8%; therefore, you want to limit your design steel to 4% to keep the steel within code limits at the splice. If you can't accomplish this, mechanical bar couplers are an option in lieu of lap splices.

 

[PUEngineer]

I believe ACI chapter 21 requires that, for special moment frames, column longitudinal bars be lap spliced at the mid-height of the column. The longitudinal bars can be mechanically spliced anywhere through the height; the type of mechanical splice depends on where in the column height, however.

 

[hokie66]

Fair enough, PUEngineer. I have never done a concrete special moment frame, don't expect to ever do one, and would refuse if asked.

 

[khinz]

why, hokie, what is wrong with concrete special moment frame?

 

[hokie66]

khinz,
I asked you some questions first. If you expect answers to yours, perhaps you should respond to other's queries.

 

[khinz]

hokie, it's the american ACI seismic code followed, the building is a special moment frame the can resist maximum horizonal shear. The main seismic system is only concrete special moment frame and nothing else, that is why it is heavily reinforced and it is only 3-storey. Why you would never do concrete special moment frame bothers me.

 

[hokie66]

I wouldn't try to design or construct a special moment frame in reinforced concrete because I know my limitations. I have never done it, and know that there are a lot of difficulties in implementing the code provisions. The code provisions are based on experience, but that experience is limited for concrete frames. There may be adequate expertise in California, Japan, New Zealand...in seismic concrete frames, but most of us are not that learned. Based on your problems in constructing a relatively minor building, it appears that the required experience may be lacking where you are located.

 

[khinz]

so what seismic provision do you use in concrete building? all shear wall? but space opening is limited for shear wall design. In my 3-storey building designed, the front and back have to be entirely open so the only supports are the columns and only special moment frame the choice.

 

[hokie66]

Maybe someone else will give you some answers, but where I have always practiced, seismic loading has been a minor consideration. Like I said, I know my limitations.

 

[msquared48]

As Clint said, "A man has to know his limitations."

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[a7x1984]

Maybe this thread should have been started in the "moment frame and shear wall engineering" category?

In Russia building design you!