Combined Section 2

[dik]

Is there an easy method of modelling a combined section in Risa 3D? I'm looking at combining two HSS 14x10x0.500 sections to produce a 28" deep section over a section of beam (the ends will be a single HSS 14x10...

Dik

 

[sbouvia]

Dik,

Yes, you could do this with rigid links in RISA. The way I do it is setting the one beam center line at zero and then setting the other beam center line at plus 14 in your case. Then adding fixed rigid links between them at like a 1 foot interval. I am assuming there could be another way, but one of the RISA guys will have to respond to you. Hope this helps.

Scott.

 

[JoshPlumSE]

There are two ways to do this:
1) The first method is what Sbouvia talks about. Model two separate members and connect them with rigid links. The only drawback with this is that you don't get shear and moment diagrams for the built-up section.

2) The 2nd method is that you can create an equivalent section (with A, I and J of the built-up section). Draw the member in at the centroid of built up section. At the ends you use a rigid link to connect the centroid of the build up shape to the centroid of the HSS14 it connects to.

This built-up member might be an Arbitray member with a General material type because the section is not quite similar to a tube. Alternatively, you could define it as a user defined Hot Rolled tube and just modify the A, I and J values to be similar to the built up shape. That would probably be conservative because the local buckling (b/t ratios) issue should be over-exagerrated in the built-up model than they would be in reality.

 

[JAE]

3) Or ignore the center flanges that occur across the mid-depth and enter it as a modified tube as a new RISA tube section (i.e. add a new tube to your member list) and design it as an HSS 28 x 10 x 0.5.

This wouldn't be perfect as your area is less etc. but if you review the conditions of loading, stress distributions, etc. it might be conservative to do so.