Central master node - Zero diagonal terms

[peppe83]

I have a floor area of 4 beams perimeter divided into 4 sections. I put in a master node in the center of the floor and I hooked up with the 4 corner nodes with rigid diaphragm. When I run static analysis and eigenvalue analysis I get the following message:"Zero diagonal terms encountered at the following nodes 1c(central node).There is some error?

[seismosoft]

Have you searched for "zero diagonal" on this Forum and/or the Help System? You should..

Seismosoft Support

[peppe83]

Hi, yes I tried but I could not find anything.

[seismosoft]

What you describe is not possible. Indeed:

- if you search the Forum for "zero diagonal", you should find 9 posts (of which 3 are relevant to your question).

- if you search the Help System for "zero diagonal", you should find 2 pages (of which 1 is relevant to your question).

Seismosoft Support

[peppe83]

I found this sentence in the forum:"Upon start of the analysis, users may be presented with a warning message regarding 'Zero diagonal terms encountered in a give node'. This means that such node is fully unrestrained in the degrees-of-freedom indicated (i.e. the node is not connected to an element or constraint capable of providing any restrain/stiffness in such dofs), a condition that, if unintended, implies the presence of an error in the assemblage of model. If, instead, such unrestrained nodal dofs have been intentionally introduced, the user may proceed with the analysis, knowing however that numerical convergence difficulties may arise more easily in such cases".

But my master node is connected to the 4 corners nodes .I don't understand the error.

[seismosoft]

Dear peppe83,

- the sentence you found is not from the Forum, but rather from the Help System. In any case, the fact that you finally managed to find it, does demonstrate that your previous statement on its inexistence was indeed incorrect.

- SeismoStruct never told you that there is an error in your model, but rather simply warned you that there are some unrestrained degrees-of-freedom. Indeed, your analysis still runs, does it not? (no need to respond, we know it does)

- and, again contrary to what you state, your master nodes are indeed unrestrained in some of their degrees-of-freedom (e.g. the vertical direction is not restrained by a diaphragm constraint, or is it?), hence the warning (not error!) message that you receive is perfectly justified.

We hope that with the above this discussion can now come to an end.

Seismosoft Support

[peppe83]

Ok, so I can leave everything as is. That's okay?
Why can not constrain the master nodes in the vertical direction.
Many thanks