Round stirrup in 4-bar configuration in a round column??

[PostFrameSE]

My fabricator would rather do a circular tie than a square tie. Is it permissible to do this in a circular column if I only have four vertical bars?.......or is there some place in the code that I'm not seeing that specifies that one must use a square stirrup for only 4 vertical bars?

Thanks

 

[msquared48]

If the column is small, I see little problem with this, particularly if it is non-structural. In fact, the circular ties would be closer to the outside of the column, better able to control cracking.

That being said, however, I never use less than 6 in a circular column. Just personal preference here. I also don't allow the lateral spacing between the bars to exceed 6".

Mike McCann
MMC Engineering

 

[fegenbush]

ACI 318-08 seems to allow this per 7.10.5.3:

"Where longitudinal bars are located around the perimeter of a circle, a complete circular tie shall be permitted."

The argument could be made that the circular tie with 4 bars violates the 135° limitation of 7.10.5.3, since the circular tie would be tangent to the bar. However, I am not sure I would make that argument.

 

[msquared48]

For circular ties, the 135 degree restriction does not apply as no circular tied arrangenent would qualify. That's where the spiral tie design comes into play.

If you want circular ties, do not allow lap splices of the ties, but normal bent ends - 180 and 90 - and have the contractor alternate where these coneections to the vertical bars occurs along the length of the column.

Mike McCann
MMC Engineering

 

[fegenbush]

msquared48,

I agree with you. The philosophical question is whether the ties are in a square pattern or four-on-a-circle. That is the point I was trying to make (rather poorly).

 

[PostFrameSE]

Thanks for the feedback! Sounds like I can do this then.

msquared48, is there a problem with just butting the ends of the tie together and welding the stirrup?

I'm using these concrete piers in an application where I'm trying to raise TS columns above the animals that occupy the same space. Due to customer preferences, I have a pier that is WAY bigger than it really needs to be.....hence my question a week or two ago regarding minimum reinforcing steel below 1% of the gross area.

My biggest issue on these piers really is uplift..........and making sure that the forces in my steel column get transfered down to the spread footing below. Due to the MWFRS design that I'm using, there's hardly even any shear at the base of the TS column / top of conc pier so I'm really not stressing things out in compression that much.

What do you think about the welding?

Thanks.

 

[hokie66]

Mike,
Curious why you say that you can't have 135 degree hook on circular ties. Done all the time, just not on the same bar like at a corner in a rectangular column.

 

[rapt]

Some codes actually require a minimum of 6 bars in a circular column. I think it is in BS8110, but it may be Eurocode.

If you use 4 bars, you would have to check the capacity at different rotations of the bar pattern (single bar at top or 2 bars at top) to determine the lowest capacity.