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Instabilities in Open Structure

Instabilities in Open Structure

Instabilities in Open Structure

(OP)
I keep getting instabilities. I have reviewed the Risa videos and attempted to manage the pin pin connections along with attempting to make the model sturdier with shorter on center spacing. Any help is appreciated. I can relieve one node but another just keeps coming up.

RE: Instabilities in Open Structure

Looks like you have columns pinned at the bottom and a pinned joint. You can do either of those but not both.

Also looks like you have no lateral load resisting system in the X direction. Are the roof beams supposed to have moment resisting connections?

RE: Instabilities in Open Structure

BootLegend is correct about the base of the columns. Though this is an inconsequential instability.... Meaning it will not affect your results. In fact, RISA is smart enough to (by default) suppress the reporting of those instabilities.

However, there is another more important instability. You have no lateral force resisting system in the global X direction. No moment frames, no braced frames. Hence the structure wants to flop over in that direction and you're getting a very real instability.

RE: Instabilities in Open Structure

(OP)
Thank you both for the comments, I had put in some corner braces at one point and I thought I just had them un-selected. I will add the braces and see the results. I did not plan on moment connections. I want to use web to plate bolted connection for beams to columns.

Thank you! I will update soon.

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