Support reactions & displacements in local co-ordinates

[Anonymous]

Hi guys,

1. Is it possible to output the nodal displacements of a support node in the support local co-ordinates? This would be very helpful but I can't see how to do it.
2. I can get support reactions in the support local co-ordinates in the reactions table, but the seismic CQC combination includes a reaction in a translational direction that has been completely released. The individual modes all have a reaction of zero in this direction, and so does the SRSS combination. Is this a side effect of the CQC process? I'm not really sure what the CQC is doing but it seems like an error if it is creating reactions like this.

Thanks,

Rory

[Artur.Kosakowski]

1. No this is currently not possible and has to be done manually e.g. after export to Excel. I have added this request to the wish list.

2. Mind that contrary to SRSS CQC include interaction between directions.

http://docs.autodesk.com/RSA/2013/ENU/filesROBOT/GUID-9A9795B9-E2B1-4F70-BC47-FF61A312699D.htm?highl...

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.

[Anonymous]

Ok I'll post-process the rotations. I take it this should be done as three rotation operations one after the other for the alpha, beta, and gamma angles, and the rotation operation is the matrix multiplication as given in the "Basic rotations" here: http://en.wikipedia.org/wiki/Rotation_matrix#In_three_dimensions. Is this correct, and what is the right order to apply these transformations? Is it the alpha (around Z axis), then the beta (around Y axis), then the gamma (around X axis) rotation? The help does not seem to state what order is assumed by the software.

The CQC formula you linked to seems to show interaction between modes, but I can't see where the interaction between directions is. The help talks about multiplying the "spectral response to the modes i and j" together (Ri * Rj) which doesn't make any sense to me. I assume this means the CQC operation is carried out for one component (such as FX, FY, MZ, etc.) at a time, and it is the same component for each spectral response mode which is multiplied together to determine the CQC value of this component. If this is the case there is no interaction between directions, so as all of my modes have a reaction FX = 0 this would mean the CQC result should still be FX = 0. Have I misunderstood something?

[Artur.Kosakowski]

 Is it the alpha (around Z axis), then the beta (around Y axis), then the gamma (around X axis) rotation? The help does not seem to state what order is assumed by the software.

http://docs.autodesk.com/RSA/2013/ENU/filesROBOT/GUID-622CF256-CA23-440D-8D09-415F561E21A4.htm

Could you attach your model please?

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[Anonymous]

Artur,

Yes I've seen that article, but it does not confirm what order the rotations are carried out in. As 3D rotations are non-commutative I need to make sure I carry out the rotation operations in the same order as Robot.

The model is very big and I'd also prefer not to post it on a public forum, but Rafal has a copy that I uploaded to an FTP site as part of a previous question as a Product Support case no. 07496072. As an example if you open the reactions table and view results for node 2510330 for case 3402 in local co-ordinates, you'll see the FX reaction for all modes is zero but the CQC FX reaction is around 114 kN. (Note that I might be looking at a slightly different version of the model as I can't remember which I sent you, but I'm sure the results will be similar for the version you have.)

Thanks, Rory

[Artur.Kosakowski]

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@Anonymous wrote:

Artur,

Yes I've seen that article, but it does not confirm what order the rotations are carried out in. As 3D rotations are non-commutative I need to make sure I carry out the rotation operations in the same order as Robot.

 

[Artur.Kosakowski]

As far as I can see the name of the file from the reference you mentioned is 120725 v3.2_case1_2012.rtd but this model has got no dynamic cases defined. I can add them providing you make screen captures that show what parameters are to be used.

[Anonymous]

From the file name it looks like that version has been converted to Robot 2012 and is not the original. Perhaps Rafal deleted them to speed up analysis. I'm reuploading the original Robot 2010 version to the FTP site Rafal provided before for that support case, it should be done in an hour or two (it's a very slow internet connection from my office!). I've also attached a screenshot of the Reactions table to show the what I mean.

Thanks for the confirmation on the co-ordinate transformations. I've put together a spreadsheet to do this and the results look OK.

[Anonymous]

Hmm I have an email notification that you have posted a reply to my last message as follows but I can’t see it on the website:

 The file is different (v3.2 comparing to v.3.6 on your picture) but the reactions seem to be correct. I have calculated the model on both v.2010SP4 and v.2013SP2.

What do you mean by correct? Do you also find that the 20 individual modes have FX = 0, but the CQC combination has FX <> 0? If this is correct please explain why this is the case. How does the CQC procedure create a reaction which is not present in any of the individual modes?

[Artur.Kosakowski]

I'm sorry I posted the answer but then I realized that you checked the values in the local coordinate systems of supports rather than the global one therefore I deleted it. I need a bit more time to investigate this further.

[Anonymous]

Ah no problem! We've now issued the forces based on these reactions, so it's a little less urgent now 🙂 I'd still like to understand what's going on to be sure there are no problems with the results though.

Thanks, Rory

[Pawel.Pulak · Accepted solution]

Hi Rory,

the effect you observe is resulting from activating "Saving results of quadratic combinations.." in Job Preferences:

After switching it off and re-running analysis CQC combinations of reactions in rotated supports are correctly displayed in the local coordinate system:

This effect is resulting from converting CQC quadratic combination of reactions in local coordinates directly from analogous reactions in global coordinates (which are already available because of active setting in Job Preferences) instead of calculating them from reactions in local coordinates for appropriate modes.

It is registered to be corrected.

As concerns obtaining the values of displacements in local coordinate systems for rotated elastic supports it can be obtained not only from transformation of global displacements using Euler's angles but also using reactions in local coordinates and stiffness vaules of appropriate supports in appropriate directions (displacement=reaction/stiffness).

Regards,

[Anonymous]

Ah thanks that did it. It has also halved the analysis time by stopping the unidentified progress bar appearing for 25 mins after the main calculations complete! Can I suggest you put a title or some explanation on that progress bar window please?! If we'd know that's all it was doing we would have disabled the feature months ago and saved a huge amount of time waiting around for results!

That's a good point - I could have put in a very low stiffness for the released direction and then used the force to determine the displacement.

Thanks guys!

[Pawel.Pulak]

Hi Rory,

the currect description of progress bars for quadratic combinations is "Saving combinations and results:"

The suggestion to improve this description was registered 🙂

Regards,