Large Pedestal Stirrup Configuration 2

[azogr]

I have a very large footing pedestal (80" x 46") that is carrying two columns. I am trying to figure out the best way to orient my stirrups and I was hoping someone might be able to clarify a few things for me. I have not decided wich size bar I am going to use for my vertical reinforcing but I am leaning towards #5's. Whichever bar I go with I am going to have quite a bit of them to meet the minimum 0.005Ag for the area of steel. What I am trying to figure out is exactly which bars across the face are going to require lateral tie stirrups.

If I am reading the code right it is going to need to be every other bar and the bars that are not tied can not be more than 6" from the adjacent tied bar. this is going to make for a very congested pedestal. Am I reading this correctly? Would I be permitted to tie every third bar since each of the two intermediate bars would be adjacent to a tied bar just not on both sides? i would keep them within 6" of course.

I would really appreciate any drawings you might be able to post with recommended layouts.

Thanks!

 

[Lion06]

I believe you are right. I don't have my ACI in front of me, but I'm pretty sure you're right.
Use larger bars (maybe #8's or #9's) to get fewer bars and consequently fewer ties.

 

[hokie66]

I don't have the current ACI code, but I think one of the requirements has always been that every corner and alternate bar has to be supported. So I think the OP was reading the code correctly the first time. I don't see that the pedestal is "congested" by following the code.

If the pedestal would work as plain concrete, then reducing the reinforcement would be acceptable.

 

[azogr]

Thank you for the responses. I would like to keep my bars smaller because I am hooking them at the top to keep my anchor bolt lengths reasonable. (I need to get a ductile failure so I am relying on my vertical dowels to pick up and carry the tension load from the anchor bolts). I suppose if I did use a larger bar I could use them straight and reduce the development length because of having an over-reinforced condition for tension.

Good point hokie66, I will investigate the unreinforced condition. I have hairpins at the top of the pedestal to handle my horizontal loads so I will not have a much moment in the pedestal (only a samll amount of eccentricity). I could supply just enough tension bars to carry the load down into the footing and leave the rest of the pedestal unreinforced. pedestal should easily be able to handle the compression loads and given its size it should easily meet the aspect ratio.

I'll let you know what I find.

 

[hokie66]

Even if it doesn't strictly comply with the conditions for plain concrete, your pedestal is not really a column. More like a beam, or probably still more like a corbel which can be designed with strut and tie methods.