Using links as column ties?

[xp1]

Have y'all ever seen links used in columns as shown in the attachment? I understand at some spots in the column, like where vertical bars splice and so they have to slope,it might not be preferable to use square ties since their size will be changing along the slope. However even then I've only seen U-bars to accommodate the sloped bars, never ties. What are y'alls opinion on these?

 

[KootK]

By "link" you mean the diamond tie, right? If so, it's very common in my jurisdiction. I believe that the intent is to leave the center of the column open and easier to pour concrete into.

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.

 

[xp1]

In this case they're making the diamond tie out of 4 separate links (like 1-legged stirrups; do these have another name?) though, is that still okay?

Actually though I didn't know that was a reason for using diamond ties, that's neat; thanks.

 

[KootK]

Ah... now I get it. I didn't pick up on the separate tie business from the picture. I've never, ever seen this done or proposed. I don't have any problem with it however. Conceptually, it doesn't seem materially different from regular cross ties.

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.

 

[Agent666]

The outer stirrups appear to be 2 u bars, in this part of the world it's a big no no to do that as there is no lapping of bars in the cover concrete unless you have a full lap length and turn in hooks into the concrete core.

 

[xp1]

Well for those U bars, I considered them okay because the required lap length is 16" which they're providing (column is 24x24.) However with those links, I was wondering if they needed to be lapped similarly and so maybe U bars had to be used. But KootK I think you're correct, they do just seem like cross ties. Thank you.

 

[Agent666]

I still wouldn't do it and I'm surprised your code allows it, if the column is subject to any cyclic loading the bond can breakdown, especially if there is an spalling of the cover concrete.

In this part of the world we generally use plain round bars for the stirrups which can't be lapped with a straight lap.

If you are trying to improve the buildability why not have one u shaped stirrup with 2 135 degree hooks with a closing link

 

[Agent666]

Just to clarify, I was talking just about the u bars in previous post. Internal links are fine as far as I can tell.

 

[xp1]

Oh! These U bars are only where the vertical bars slope, which happens about 4" below a beam intersection to within the intersection; so for the most part within the beam cage. At all other locations we require closed ties. Would you still think there's an issue with this?

 

[Agent666]

Ok got it. I've never seen a smaller stirrup being used in the region where the bars crank in at a column lap. Usually the main stirrups just carry through with a bit of a gap to them.

Never given it much thought to be honest, so not sure what others do?