Diaphragm rigid

[ehsanala]

hi

how can with equalDOF command in 2D model to made Diaphragm rigid?
with equalDOF $rNodeTag $cNodeTag 1 2
or
with equalDOF $rNodeTag $cNodeTag 1
?why?

regards

[fmk]

the equalDOF sets the dof at the nodes to be equal for those dof you specify .. you are asking is it the 1 and 2 dof or the 1 only .. so ask yourself what is is you want to achieve and the answer should be obvious.

[ehsanala]

hi

What should be to made rigid diaphragm in 2D the frame?

thank

[fmk]

if you need to ask this you should not be using it! you need to understand what it is before you use it. i suggest a little research. it will aid you in the long run if you know what it is the computer programs you use are actually doing.

[civil]

Hi dear all;
Is it necessary to define equalDOF in 2D moment resisting frame?

[fmk]

depends on your structure. but no not necessary

[civil]

could you please explain it ?
how it depends on structure?
I want to consider rigid Diaphragm influence in my 2D moment resisting model.

[fmk]

you are modeling a structure. if you assume rigid diaphragm you are saying that the translational dof between the nodes at a floor do not move. you simply have to ask yourself based on the structure you have whether this is a realistic assumption. if you do use equaldDOF make sure you are not using the nonlinearBEamColumn (forceBeamColumn) for the beams in the model as the axial forces will end up being unrealistic because of the constraint.

[civil]

1- did you mean for consideration rigid diaphragm in 2D model i have to use equal DOF?
2- if I use nonlinearBEamColumn (dispBeamColumn) and equal DOF, every thing is ok?
3- if I use nonlinearBEamColumn (forceBeamColumn) i coudnt use equal DOF ? so what should i do in this case?
4- how can i consider rigid diaphragm for 2D model in opensees (except equal DOF)?

[fmk]

1. that or rigidDiapragm or model it using elements
2. yes.
3. yes. use the dispBeamColumn.
4. account for it in your model. it would be more accurate thing to do (nothing is rigid) but the more time-consuming.

http://opensees.berkeley.edu/wiki/index ... r_Elements

[civil]

Thank you very much dear fmk
your answers are very useful

could you please explain "using elements"? how?

[fmk]

you model it specifically in your model. it is a structure after all and no structure is built using something called a rigid diapragm. they are built using concrete and steel.

[civil]

Thanks dear fmk. but i dont understand how can i define Diaphragm rigid in 2D model by using elements!

[fmk]

e.g. the beam section might include the tributary area of the slab, you caould also add a truss element with a large axial stifness between the nodes, the possibilites are endless.

[Tas]

fmk wrote:
> 1. that or rigidDiapragm or model it using elements
> 2. yes.
> 3. yes. use the dispBeamColumn.
> 4. account for it in your model. it would be more accurate thing to do
> (nothing is rigid) but the more time-consuming.
>
>
> http://opensees.berkeley.edu/wiki/index ... r_Elements

An "objection" concerning points .2 and .3 of your answer. Either for FBE(forceBeamColumn) or DBE(dispBeamColumn), if they are used to model beams, it is not precise to use equal DOF because of the development of additional -unwanted- axial forces and moments to them. Actually, it is because the use of RC fiber section approach that causes shifting of the neutral axis either if they are used for FBE or DBE (see Vesna's presentation: "Modeling Diaphragms in 2D Models with Linear and Nonlinear elements" 2011). All these concern RC elelments (not Steel).
I suppose that there would be no problem if instead of using fiber section someone uses other type of section (e.g uniaxial, aggregator) when defining FBE or DBE...