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Proper Way to Input Multiple Members between 2 nodes in Risa3D

Proper Way to Input Multiple Members between 2 nodes in Risa3D

Proper Way to Input Multiple Members between 2 nodes in Risa3D

(OP)
I'm curious if there is a way to design with multiple steel beams between two columns. In other words, I'd like to have two beams and two braces attached to one column. When I try, seems that one of my beam mebmers gets stressed way more than the other, even though loads are even and each beam member is attached to the same nodes.

RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

Is one of your beam & brace combinations made of significantly stiffer members than the other? If so, the results may be accurate.

This may be a good application for a three dimensional model that can capture more complex behaviour.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

If you post this question in the Risa Technologies: RISA 3D forum, Josh Plum will answer. He is the residing RISA expert. You will have to redflag this string and request it be removed though if you do.

Mike McCann, PE, SE (WA)


RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

Are your beams at different elevations? or are they stacked? Any composite action?

If one is sitting on the other with no composite action, then place the two beams a small amount apart and add multiple rigid links between the two. That's how i'd do it, but others probably have more elegant ways.

RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

(OP)
Thank you all for the answers so far. What I have is two cee channels attached to a single column. The cee channels are separated by the width of the post, having the webs screwed to outsides of the column. Each beam has a cee channel brace attached to the column. Hopefully this clarifies it.

RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

I'd just model it as a single member that represents the back-to-back channels. Keep an eye on things to make sure that the proper effective lengths are used for buckling and LTB. If the cee channels are identical on either side of the column, then it sounds as though you are getting spurious results.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

(OP)
Thanks, Koot. That is what I had in mind. I don't know how to do the input. For wood, there is an option for multiple members. I'm using v7.1 release, so not sure if they have added that functionality.

RE: Proper Way to Input Multiple Members between 2 nodes in Risa3D

Seconded KootK's solution. You'll want to create and input a custom equivalent shape or section set. Be careful that your moment of inertia about the web axis correctly accounts for the channels being independent/partially composite/composite depending on their connection to each other.

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