RC Column stirrups 2

[mar2805]

HI!
Can anyone maybe explain a benefit of using stirrups on the left instead the ones on the right?
Same column with 8 bars, except the right one has identical stirups shape and the one the left has 2 stirrups shapes.

 

[rapt]

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.

 

[jayrod12]

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).

 

[mar2805]

YOu would apply the same solution for boundary shear wall elements?
Top solution instead of the bottom one?

 

[Agent666]

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.

 

[Trenno]

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

 

[JoshPlumSE]

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.

 

[Trenno]

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.

 

[Agent666]

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

 

[wannabeSE]

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

 

[Agent666]

Yes.

 

[mar2805]

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?

 

[Agent666]

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

 

[mar2805]

I think that stirups laping is something you have like in the picture attached and ITS VERY DIFFERENT FROM CLOSED HOOK SHAPE like I posted in my 1st post.

 

[Agent666]

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?

 

[mar2805]

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

 

[Agent666]

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

Does that make sense now?

 

[mar2805]

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?

 

[Agent666]

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?

 

[mar2805]

"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.