topic Re: Combine Time-History with Static load cases? in Robot Structural Analysis Forum

Combine Time-History with Static load cases?

Anonymous — Wed, 03 Oct 2012 16:17:21 GMT

Hi,

I would like to combine a time-history analysis with an existing static load combination within ROBOT. Is this possible?

I have seen the 'Consider results from a selected case as initial ones 'tick box, however load combinations cannot be specified there.

Thank you for your help.

Regards,

Stuart

Re: Combine Time-History with Static load cases?

Anonymous — Wed, 03 Oct 2012 23:39:00 GMT

When you define the THA, you need to select a case that it is based on.

Just make this the static case you want to use for the THA and apply the forcing function. The "consider results" just means forces and displacements from the case you enter are the basis for the THA.

Re: Combine Time-History with Static load cases?

Artur.Kosakowski — Thu, 04 Oct 2012 07:16:08 GMT

You need to convert THA components into simple load cases first. Then they can be used in definitions of combinations.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Combine Time-History with Static load cases?

Anonymous — Thu, 04 Oct 2012 07:34:02 GMT

Thank you for your help.

This is not quite what I am trying to achieve. Appologies for the vagueness of my first question.

What I would like is for ROBOT to apply a load combinaton to the model and solve it statically.

Then, use this static case for the starting point for the THA analysis. I would like to apply the THA in addition to the already applied static load combination.

The load combination is the combination of the dead weights applied on the structure. (they are also included in the load to mass conversion for dynamic analyses)

Thank you again for your help.

Regards,

Stuart

Re: Combine Time-History with Static load cases?

Artur.Kosakowski — Thu, 04 Oct 2012 07:46:24 GMT

Stuart,

In such case you need to create a simple load case with loads as in the combination you would like to use as the starting load case first. This simple load case has to be defined before THA case. Finally you should type its number in the field indicated below:

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Combine Time-History with Static load cases?

Anonymous — Thu, 04 Oct 2012 08:22:02 GMT

Arthur,

Thank you for your help.

Just to confirm. I have to apply the dead loads in one simple load case?

Is there not a way to use a load case combination for this 'initial case'?

Regards,

Stuart

Re: Combine Time-History with Static load cases?

Anonymous — Thu, 04 Oct 2012 08:30:19 GMT

Appologies for the many questions.

Is dynamic mass accounted for in the THA?

If I was to need a number of different 'initial cases', with different dead loads, i.e. the models have different mass distributions. Would I need completely separate models?

There only appears to be options to apply the mass to 'Global Mass', 'Dynamic mass' or modal analyses.

Thanks again for your help.

Regards,

Stuart

Re: Combine Time-History with Static load cases?

Artur.Kosakowski — Thu, 04 Oct 2012 08:32:04 GMT

Just to confirm. I have to apply the dead loads in one simple load case?

Correct.

Is there not a way to use a load case combination for this 'initial case'?

Currently the option is limited to simple load cases. This is related to the way of accessing the results (results of linear combinations are not stored directly but created based on results of simple load cases).

Regards,

Stuart

Re: Combine Time-History with Static load cases?

Artur.Kosakowski — Thu, 04 Oct 2012 08:39:16 GMT

Is dynamic mass accounted for in the THA?

Yes, it is.

If I was to need a number of different 'initial cases', with different dead loads, i.e. the models have different mass distributions. Would I need completely separate models?

No, but you would need to create several groups of modal and THA cases (modal 1 followed by THA1, modal 2 followed by THA2 etc.). The load to mass conversion should be done for specific modal case (it will be then used for the following THA case) and inside the THA case that follows 'its' modal case you define the appropriate staring case.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Combine Time-History with Static load cases?

Anonymous — Thu, 04 Oct 2012 09:08:34 GMT

Thanks again Arthur.

So, the THA is always linked to the last modal analysis which was carried out for both the participating modes and the dynamic mass?

Is this the same for spectral analyses also?

Regards,

Stuart

Re: Combine Time-History with Static load cases?

Artur.Kosakowski — Thu, 04 Oct 2012 09:14:27 GMT

Yes, they use parameters form the modal case defined prior to them.