Axial Load in Braced Frame Beam

Question

Axial Load in Braced Frame Beam

kmccain1 (Structural)

(OP)

11 Jul 13 17:50

I have multiple, non-symmetrical braced frames resisting wind modeled in Risa 3d. I applied the wind load to a single point attached to the rigid diaphragm at each level. Risa provides the axial load in the diagonal braces, but my question is if there is a way to trick Risa to quickly show the axial loads in the beams of the braced frames as well. (As I have it now I assume Risa attaches all of the horizontal beams to the diaphragm so they do not show any tension/compression) Hope this makes sense.

structSU10 (Structural) · Answer 1 · 2013-07-12 07:37:10

I don't know a way to do it that is easy. You could create more nodes on the beam that are disconnected from the diaphragm, but I don't know if that will get you a very accurate result. I would think the easiest way is to get the frame shear from your model, apply it to a seperate model for the frame, and get the axial forces from that.

JoshPlumSE (Structural) · Answer 2 · 2013-07-16 10:18:44

In RISA, you can look at the properties of the joints on the beam. Either in the Joint's double-click dialog, or in the Joint coordinates spreadsheet. You will see a box titled "Detach from Diaphragm". If you check this box, then that joint will not directly connect to the diaphragm. If you are careful with which joints you do this for, then you can get the diaphragm forces to drag through the beams into the braced frames.

It's not a perfect solution and it won't work for all models. But, it does work most of the time if you are careful.

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Axial Load in Braced Frame Beam