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Civil Engineering/Etabs - Structure is Unstable

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Question
Typical floor
Typical floor  
QUESTION: Dear Sir

Incontinuation to my earlier Question

(Dear azhar

Remove the joint and let me know the result. It appears to me a redudant joint which cen be removed.

Regards
BEH)


Points Which are Visible in Photos are CG, Centre of mass Points of the Structure
There are no joints in the panel,
where i have marked location of warnings

Warnings are coming close to those points

Please suggest what could be the reason

ANSWER: Dear Azhar

A joint exists there, there is no doubt.

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: Dear Sir

1.
i have Rechecked my model,
removed all the Redundant joints if were there

What i have done is in set building view option un selected all, except points
then selected all the points then deleted, so that any redundant joints gets removed
Same warnings are coming again

2. Presently rigid diaphragm has been assigned to slabs
  if iam assigning as semi regid, then warnings are not coming at those locations
Structure is stable - is this ok if i was consider as Semi rigid Diaphragm
or when we need to consider as Semi rigid

ANSWER: Dear Azhar

It is true that very high stiffnesses lead to excessive error and artificial instability. I suggest you to use a true model of slab and remove the rigid diaphragm. The slab model will have the effect you need.

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply sir

Sir
How to use a true model of slab?

Answer
Dear Azhar

Rigid diaphragm is a hard model for the slab to make us able to constrain all joints of a floor together. This is a model used essentialy by non building structural analysis softwares like sap2000 to model the slabs effect. For etabs it is ok to use the slab model like shell or plate without any assignment of rigid diaphragm. The slab model do as a rigid diaphragm .

Regards
BEH

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