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StuartRogers
Posts: 25
Registered: ‎03-07-2012
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Combine Time-History with Static load cases?

541 Views, 10 Replies
10-03-2012 09:17 AM

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

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tony.ridley
Posts: 652
Registered: ‎09-07-2011

Re: Combine Time-History with Static load cases?

10-03-2012 04:37 PM in reply to: StuartRogers

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. 

Untitled.jpg

 

 

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Artur.Kosakowski
Posts: 4,777
Registered: ‎12-17-2010

Re: Combine Time-History with Static load cases?

10-04-2012 12:16 AM in reply to: StuartRogers

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

 

THA combination.PNG

 

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Artur Kosakowski
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StuartRogers
Posts: 25
Registered: ‎03-07-2012

Re: Combine Time-History with Static load cases?

10-04-2012 12:34 AM in reply to: Artur.Kosakowski

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

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Artur.Kosakowski
Posts: 4,777
Registered: ‎12-17-2010

Re: Combine Time-History with Static load cases?

10-04-2012 12:46 AM in reply to: StuartRogers

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:

 

THA initial.PNG

 

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.



Artur Kosakowski
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Contributor
StuartRogers
Posts: 25
Registered: ‎03-07-2012

Re: Combine Time-History with Static load cases?

10-04-2012 01:22 AM in reply to: Artur.Kosakowski

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

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Contributor
StuartRogers
Posts: 25
Registered: ‎03-07-2012

Re: Combine Time-History with Static load cases?

10-04-2012 01:30 AM in reply to: Artur.Kosakowski

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

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Artur.Kosakowski
Posts: 4,777
Registered: ‎12-17-2010

Re: Combine Time-History with Static load cases?

10-04-2012 01:32 AM in reply to: StuartRogers

 

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


 



Artur Kosakowski
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Artur.Kosakowski
Posts: 4,777
Registered: ‎12-17-2010

Re: Combine Time-History with Static load cases?

10-04-2012 01:39 AM in reply to: StuartRogers

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.



Artur Kosakowski
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Contributor
StuartRogers
Posts: 25
Registered: ‎03-07-2012

Re: Combine Time-History with Static load cases?

10-04-2012 02:08 AM in reply to: Artur.Kosakowski

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

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