Precast Column Base Connection to CIP Pilaster of Same Size

[KootK]

Normally, when I put a precast column on a CIP pilaster, I'll make the pilaster larger than the column by 3"-4" on all sides. That, to provide some tolerance and so that a standard four bolt precast base connection can be used without interference between the anchor bolts and the pilaster reinforcing. On a current project, I'm being asked to detail a precast base connection where the column and pilaster will have identical cross sectional dimensions. Is there a reasonable way to do that that is not cost prohibitive?

These are some options from a manufacturer's catalog for slightly different situations. One seems to show same sized precast columns successfully connected but I'm not sure if that would apply to a CIP pilaster. Also not sure how it was done.

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[TehMightyEngineer]

Hmmm, a good question. Does the column have significant flexural load or is it primarily axial?

I could think of a few ways to do it but no idea if it's feasible or cheap. Probably depends on the pilaster reinforcement and the loads involved. Can you provide a trademark KootK sketch of the pilaster and column reinforcement setup?

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[WARose]

How you detail it in the last pic is pretty close to what I've seen. If you look at it in the PCI handbook (5th edition, p. 6-24) they show something similar....and that is for a small column on a big pier.

 

[KootK]

Do you know how that last pic would work on a CIP pier where both column and pier are the same size? Seems to me that the anchor bolts and column cage would be all over each other.

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.

 

[WARose]

Do you know how that last pic would work on a CIP pier where both column and pier are the same size? Seems to me that the anchor bolts and column cage would be all over each other.

I would think close to how you have it. You'd just have to have that bolt gauge small enough to miss the ties/vertical reinforcing on the perimeter.

 

[JAE]

Could you relocate your column anchor rods to be centered on the face of the precast columns (instead of the corners) to avoid the conflict with the corner bars below?
You might have to splay out the block out sides to allow better approach to the anchor nuts with a wrench.



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[KootK]

Thanks for your help so far gentlemen.

I would think close to how you have it. You'd just have to have that bolt gauge small enough to miss the ties/vertical reinforcing on the perimeter.

Hmmm... it hadn't really occurred to me that I could tinker with the bolt gauge. I thought 2" was kinda "it" based on 4" angles in the corner. I'll explore that with the precaster if they ever return my call(s). Based on the geometry that I'll mention in response to JAE, I think I could make this work with 5 x 5 recess angles instead of 4 x 4 giving me 3" to the anchor bolt centres. This only reduces the cross sectional contact area by 5%

Could you relocate your column anchor rods to be centered on the face of the precast columns (instead of the corners) to avoid the conflict with the corner bars below?
You might have to splay out the block out sides to allow better approach to the anchor nuts with a wrench.

Yes. I think that I can even improve upon that though. On two opposing sides (front/back), the pilaster will be larger than the PC column in order to create a ledge for incoming hollow core. This will move the anchor rods away from the tight corner area just as you have proposes. Bloody brilliant..

Now that I think of it, if desperate, I might even have other options here owing to the pilaster being longer, one direction, than the precast columns. I could plop some 3 x 3 clip angles on the sides of the column, outboard, and get it done that way.

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.

 

[birneys]

Another option would be to use a grouted sleeve connection instead of standard anchor bolts. I used them for several large precast columns that were part of a large precast moment frame when standard anchor bolts didn't have the capacity we needed. Essentially, there is a sleeve that is cast into the precast column, and you extend dowels up from the CIP foundation/pier. Then you slide the precast column down over the dowels and grout them in place using grouting ports that were cast into the column with the sleeve.

This is a schematic detail, but it might help you solve your congestion issue if you can use the reinforcing to also make your column connection. One thing to keep in mind is that the sleeves are not cheap. It does leave you with a very clean connection when you're all done.

I don't remember the specific product that the PC manufacturer used, but I know Dayton Superior makes one (see page 113 here).

 

[dik]

When I did Kingsway Square I used similar details to those in KootK's first posting, but designed the baseplate for the column loading only, with no structure on top... then grouted the anchor rod pockets to take care of additional loading from the tees and slab over. Had hundreds of columns so minimising the plate thickess has some savings.

Dik

 

[hokie66]

Agree with birneys about grouted sleeves. We normally use corrugated post-tensioning ducts with grout tubes.

 

[Guest262653]

Probably you already know it, but Peikko has some column shoe solutions that might be interesting for your case:

https://www.peikko.com/products/bolted-column-connections/overview/

https://media.peikko.com/file/dl/i/yGix0w/0ZFj6oWsDyxeMUHvUgp3oA/peikko_columnconnections_final.pdf

 

[Brad805]

I too would use grout tubes in the precast, with projecting rebar from the pedestal. One, two or four depending on your load and column size. Pay attention to how the dowels fit in the precast. Your dowels tend to be inset a good distance from the edges to get it all to fit within typical tolerances. If you have larger bending forces, NMB splice offers a good product:

http://www.splicesleeve.com/

You have to use their grout, and that can be a coordination issue for your trades if there is not a source anywhere near you.

I do not think the Piekko base connections will work very well in this case where the sizes are equal.