rigid diaphragm

[senior]

i have big model (15 and 30 stories and time history analysis). it is 2d .
someone told me if you define rigid diaphragm, your results will be incorrect and yo will certainly have analysis and convergence errors.
is it true?

[brag006]

how are you defining a rigid diaphragm?

[cxc08]

dear senior,
Could you please explain more about your model?
Here is some discussion about rigid diaphragm. It may help you.
http://opensees.berkeley.edu/wiki/index ... nsequences

[hnaderi]

if you use equalDOF command for modeling rigid Diaphragm in 2D frame, Moment and shear forces may be incorrect.
i think only in 2D RC frame with force beam-column (nonlinearBeamColumn) and fiber section.....(It depends on your model....YOU Should CHECK IT OUT)

look at the following :
http://opensees.berkeley.edu/wiki/index ... r_Elements

[senior]

brag006 wrote:
> how are you defining a rigid diaphragm?

i write:
rigidDiaphragm 3 11 12 13 14 15 16 17
for second story for example : 21 22 23 ...
but it doesn't work.

my model is 2d and it has 15 stories.

[hnaderi]

you can't use rigidDiaphragm command in 2D.

look at the following :
http://opensees.berkeley.edu/wiki/index ... gm_command
NOTE: The rigidDiaphragm command works only for problems in three dimensions with six-degrees-of-freedom at the nodes (ndf = 6)

[brag006]

just use equalDOF command. I think it has the same function

[xiell]

Firstly, rigid diaphragm can only be utilized in 3D model.
Secondly, if you want to restrict the displacement of four nodes, you can add two truss elements with large axial stiffness between two nodes in the diagonal derection. I have validated the reliability of this method both in 2D and 3D model, you can try it.