Why moment frames is not seeing any lateral load?

[compe_ad]

Hi! I am modeling a structure in ETABS. I tried two different model. One with rigid diaphragm and another with semi rigid diaphragm. Floor for my structure is modeled as a bare steel deck. For the case with rigid diaphragm my moment frames are not taking any forces. Can you please help me understand why is this happening? (see attached pic).

 

[sticksandtriangles]

It is likely that your deck is not very stiff, therefore in your semi rigid diaphragm model, your model is probably very closely mimicking a "flexible diaphragm" where load is distributed based on tributary area.

With a rigid diaphragm, your loads are distributed based on the stiffness of the LFRS, not trib area. Your moment frames are likely very flexible as compared to the shear walls, therefore you dont see any loading in the moment frames.



S&T -

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[JoshPlumSE]

This is likely just a case of relative stiffness. If the shear walls are 100 times more stiff than the moment frames (in terms of deflection per inch) then they will take 99% of the load if you've got a rigid diaphragm. Right?