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RC Column stirrups
2

RC Column stirrups

RE: RC Column stirrups

The one on the left is a much more rigid arrangement to tie the whole thing together during placement and concrete pouring. There is much more movement possible in the one on the right.

RE: RC Column stirrups

Yeah I'm with rapt. I'd bet the rebar monkeys prefer the detail on the left for rigidity of the assembly. The only benefit to the one on the right is the same sized stirrup for all, so you're saving a fabricator time (that he's not going to forward onto the project in terms of cost savings).

RE: RC Column stirrups

The stirrup set on the right in the first attachment also may need the overlap to be a full hooked lap depending on your codes rules for lapping stirrups in the cover concrete, for plain round bars this is 2xLdh.

RE: RC Column stirrups

The outer full loop link will also help if the column is ever subject to torsion.

RE: RC Column stirrups

I disagree with Trenno. Once these are constructed, they should behave essentially the same. IMO, any difference is solely related to ease of construction or fabrication.

RE: RC Column stirrups

If the lap between the green and the blue links is sufficient, then yeah it would work.

But say you have 12mm links, then the lap length would be around 40*db = 480mm. You wouldn't space longit. bars further than 300mm in columns, more like 150mm. In this case (typical) the lap isn't achieved.





RE: RC Column stirrups

double that length as well if you're using them for shear in some codes (if plain round bars).... rapidly becomes a silly idea.

RE: RC Column stirrups

Shouldn’t you be looking at hook development length rather than lap length?

RE: RC Column stirrups

Yes.

RE: RC Column stirrups

(OP)
Agent666 and Trenno,
are you aware of your statements?
Are you certain of what you are talking aboth?
See picture attached.
You want the lenght "L" to be a full tenssion overlap between the two bars?

RE: RC Column stirrups

Of course?

Don't know where you are located as you didn't say. But many standards contain requirements for lapping stirrups in the cover concrete. For example this what NZS3101 has to say on the matter. A plain round bar has 2xbar development length in NZS3101.

Our standard is loosely based on ACI318, so you may/may not find similar provisions in ACI, to be honest haven't really looked. All I'm saying is these provisions exist for a reason, so investigate what your local standard has to say on the matter


RE: RC Column stirrups

Of course it's different. But the requirements still require a full lap with hook turned into the concrete core under certain circumstances.

So where are you from, what does your code say on the matter?

I'm assuming you have loads in the long direction, correct?

RE: RC Column stirrups

(OP)
Can you use my picture and draw the "full lap with hook" you are talking aboth.
It would be easier to understand.

RE: RC Column stirrups

Sure, the stirrup leg does the same thing from each side effectively as a hooked anchorage. i.e.



Does that make sense now?

RE: RC Column stirrups

(OP)
It doesnt.
If you could draw you own column and sketch stirups and they arrangement.
My drawings always contained closed stirups shape.
You are talking aboth open shape stirups that need to be spliced?

RE: RC Column stirrups

Yes your drawings contain closed stirrups, the hook (bend) around the bar going into the concrete is effectively the same as the extension on a standard hook in this scenario. The two extensions are the same bar with a closed stirrup.

The closed stirrups are fine, I'd do exactly the same. However the point is you may need the lap or overlap between the two separate closed stirrups to be sufficient to achieve a development length like the sketch I have marked up in the last post. I'm not sure how to articulate it any other way?

On the sides of the column where you have the stirrups overlapping, the overlap may need to be a code compliant lap (i.e. L_dh). This may depend on what standard you are working to, but either way it is a good detailing practice. If the bar is plain round bar, then it is usual that 2 times the standard lap for deformed bars is required.

I've asked twice now where you are from and what code you are working to so I can see if there is more specific advice in whatever standard you are designing to, can you let us know so someone can comment if there are similar provisions in that code?

RE: RC Column stirrups

(OP)
"I'm not sure how to articulate it any other way? "

One more time, please draw a sketch of a real world case you had, so we can see your column stirup detailing.

RE: RC Column stirrups

We're here to help you mate, a simple 'please' wouldn't go astray.

RE: RC Column stirrups

Hi mar2805, I've never had a real world case in a column because in my opinion it's an inferior detail and my preference is for the outer stirrup to be one piece. This stems from a number of things, but one that people have not mentioned is that you're giving the ability for the two closed stirrups to move apart and violate covers on both end faces. At least with a single closed stirrup it can be detailed to achieve the cover all round, contractor still has to put it in the right location, but there's less opportunity to get it wrong.

You seem to be asking the same question over and over, which I believe I've tried to answer several different ways. So either I'm missing something obvious that you're after or you are missing something? If the below doesn't answer your question then please elaborate on what your particular concern is in more detail and someone else may be able to assist?

But here's an example of a wall detail from another engineer. Real world case looks exactly like your sketch but with sufficient lap length between the individual stirrups. In this case the bars were plain round bars, if they were deformed bars presumably the 450mm min lap could be halved.




RE: RC Column stirrups

2
@OP: it would be helpful to know more about you application. Where in the world will your project be located? Is this a high seismic, high ductility application?

Other comments:

1) For the case of overlapping tie sets, I believe that there will be many instances in which it will not be required to lap the neighboring ties. The first step with this, I feel, is to identify what job(s) it is that your ties are actually doing in your design. Often, as I would expect in OP's case, the ties are provided for confinement and vertical bar buckling only and are not intended to function as the wall horizontal shear reinforcing. When this is the case, shear is transferred across the length of the ties sets by horizontal bars that run either within the zone cage or outside of it, depending required ductility and local code rules.

2) Like others, I avoid overlapping tie sets, primarily, for reasons of constructability. Some not yet mentioned aspects of this are mentioned in the paragraph below taken from this article. For a relatively short zone like OP's I'm all about option [b] in the figure below. For very long zones, especially prefabricated ones, I think that the best approach is to break the tie set into separate modules entirely and detail shear transfer between them as required.


RE: RC Column stirrups

(OP)
Guys sorry for the delay.
Agent666, thanx for posting your picture.
Im Eurocode based
I understand what you ment, but I think that your idea is more closely related to Shear Wall boundary elemnt detailing then to columns....but ok. I understand what you mean and I can agree with those hook overlapps, but then, we get to KookT figure 5C situation...So I think it would be better to provide one BiG external hook and then smaller "inner" hooks. The big external would be probably limited in lenght...for egsample in Europe, we never had hooks that were longer then 2 meters. That hook would enclose an shear wall boundary element thats approx 0,9m meter long.

RE: RC Column stirrups

Since you're Eurocode based, I'll try to answer your last question. For DCM you need a stirrup holding a longitudinal bar at every 20 cm, and for DCH at every 15 cm. In case A you have a stirrup leg every 2s. If 2s < 20 (15) then it's okay, but i doubt it is. To me, kootk's example (b) seems like the best solution for walls considering both performance, simplicity and construction.

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