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# Concrete columns issue

## Concrete columns issue

(OP)
I am a new user of Risa-3d and I have a question for concrete columns.

Imagine a 3-floor house with concrete columns (30cm x 150cm) on the corners. My problem is that I don't know how to design them in Risa3d in order to connect the beams to the columns and get the moment diagrams of these columns. I have tried putting 3 joints in a row (distance between them = 75cm, joint numbers for example N1, N2 and N3) and connecting the beams to joints N1 and N3, and draw the column on joint N2 with width 150cm. Is that a correct approach of the problem? Is there any other way to do this?

### RE: Concrete columns issue

Not sure I fully understand your question. Though the normal way to model is to use "centerline" modeling. Columns are drawn at their centerline locations and beams are assumed to span from centerline of column to centerline of column. Does that answer you question at all?

Some folks like to use "rigid end offsets" for the end of their beams. That way the beam is still modeled from centerline of column to centerline of column. However, the rigid offset designation adds rigidity to the beam between the face of the column and its centerline.

### RE: Concrete columns issue

(OP)
Just to be more specific, I upload a photo which I believe will make things clear. I understand the "centerline" modeling but I think I can not use it in this situation...(my guess...)

As for the rigid end offset you said, I have no idea what it is but I will search for it.

Thank you very much...

### RE: Concrete columns issue

Good picture. That's exactly what I thought it was. You want to use centerline modeling. Then adding rigid end offsets to your centerline model will accomplish what you're trying to do with that second approach.

You can access rigid end offsets a number of ways. The easiest will be to double-click the beam to bring up the member info dialog. On the General tab there is an "advanced" section which specified the rigid end offset dimension. Note: you can also specify a member label to base the offset on half the dept of the member.

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