rho factor for modal analysis procedure

[OUe]

Do I use rho if the dynamic analysis falls between the elf and elfxrho?

ie:
Vmodal = 137 kips
Velfxrho = 167.4 kips (rho=1.3)
velf = 128.8 kips

I'm a little new to dynamic analysis with section 12.6 of ASCE 7-10, so any corrections/comments are welcome. I'm using RISA.

 

[OUe]

Another question I have is whether a steel plate used as a "plane stress" plate in RISA will behave like a horizontal diaphragm and grab all the members crossing the plate. I'm looking at certain mode shapes and some of the members look as though they are buckling out of plane on the edges. I'm wanting accurate results for the modal analysis, but it almost seems as though I will need to have a dynamic analysis separate model for modeling things that aren't "true" just to get a solution. Has anyone else encountered this?

 

[WinelandV]

I can't speak to your first post, but as for your second, plates in RISA only connect to other plates and beams at the corner nodes. Otherwise, the beam and plate will behave independently of each other. This means that if you need to have the plate affect the beam along the length of a beam, you will need to have lots of little plates so that the corner nodes can fall on the beam, creating continuity at those nodes.

You may also want to check out this thread: thread1419-294774

 

[OUe]

Thanks windlandv!