2 identical models except for the fact that one of them has axial damping (Bar releases) on the X braces .
Help file from Bar releases says " The damping value is considered only in the time history analysis" .
But the modal analysis results are completely different.
files are here
http://www.4shared.com/rar/a3EfBUXCce/50ANDARES_analise_modal_NR.html
http://www.4shared.com/rar/DITxjswyce/50ANDARES_analise_modal-dampin.html
thx
Rafael Medeiros
Robot Structural Analysis
Solved! Go to Solution.
Solved by Pawel.Pulak. Go to Solution.
You can modify the damping (global) coefficient when you run a modal (spectral) analysis.
In the link that rafascudo attached (Taylor's devices) it writes some interesting things about it.
Just a comment to what i said in my previous post:
The global damping factor can be modified in case of using linear viscous damper (as the fluid viscous dampers are) and as far as i know it is the most common practice for this kind of dampers (although the dampers have to be placed properly distributed over the structure).
If someone (including the supporting team of course) has any kind of experience on the implementation of dampers in Robot (linear viscous or other kind) it will be much appreciated to tell us more.
Some comments to remarks of Rafascudo, t.sautier and Tuctas - apologies that so late
The most suitable definition for fluid viscous damper is 1) from this post, i.e. "free + damper"
Damping in advanced parameters of modal analysis does not influence modal analysis but seismic analysis following it (somehow misleading ) - like eta damping correction factor in EC8.
Tuctas also mentioned using global damping factor instead of dampers in case of dampers properly distributed over the structure - in case of THA it can be defined in Damping parameters of this type of analysis (direct values of relative damping for the modal decomposition method or via Alpha and Beta values for other methods)
I hope it helps.
Regards,
I'm working with Rafacascudo in the same project, where we're trying to use these dampers.
I'm having a problem with time-history analysis. I'm now trying to discover the structure response wihtout any damping. I have to use the non-linear analysis so I'm able to use the free dampers later and compare the results.
The thing is, when I choose the newmark method (acceleration), the response diagram behaves as if there's some kind of damping, even when I use alpha and betha constants as 0 and also the damping constant as 0 in the release definition. Is there somewhere else where I should define the damping I want?
If I use the modal decomposition method this doesn't happen, but then I can't add dampers later.
thanks
Hi all,
On studying this case , some doubts about the program results led us to do some tests using a small frame model.
1- For TH case ,Sinodal F-T function according to 1st mode frequency is applied to VENTO1 Load case.
2- Brace is fully axially released at the botton and a damping coefficient is applied.
3- If the TH analysis is linear , everything behaves as expected
4- If the TH analysis is Non-linear or P-delta , the structure behaves as if there is no damping applied to the brace and only the global damping acts.No matter what value is assigned to the brace damper , the results are the same.
5- Calculated Total mass(739,39kg) on modal results doesn´t match with structure total mass (1048kg , on quantity survey)
Model is attached
Rafael Medeiros
Robot Structural Analysis
I tried to run this simple case. If I use linear analysis it works just fine, but when I try to use non-linear analysis, the dampers don't work, and there's no effect on the structure. Is there any way I can use these dampers in a non-linear analysis?
File attahced.
This can be called a "synchronized " post!!!
Rafael Medeiros
Robot Structural Analysis
Any ideas of why this is happenning??
Rafael Medeiros
Robot Structural Analysis
Confirmation. Unfortunately if Non-linear or Non-linear and P-delta analysis is activated in time history analysis the dampers existing in the model are ignored.
Reported to dev team.
Regards,
Thanks Pawel!!
I did some futhers tests and this happens not only when you activate nonlinear/Pdelta on TH window checkboxes.
Having a nonlinear element like a tension only bar or an uplifted support ,is enough to deactivate the damper.
This happens even if this nonlinear element is only present on a separate structure on the same model.
Any chance of this being corrected in the incoming service pack??
thx
Rafael Medeiros
Robot Structural Analysis
It was reported with high priority but after completing development for RSAPRO 2015 Service Pack 3 which is already published.
Regards,
Pawel ,
I tried to use damping through compatibles nodes or supports as a workaround for this problem , but it also didn´t work when nonlinear is choosen.It worked perfectly for Linear analysis
Is there any other workaround to solve this problem , or for now , any kind of damping is incompatible with any kind of nonlinearity??
Was this always like that or it worked in any of the previous versions of the program??
thx!!
Rafael Medeiros
Robot Structural Analysis
@Rafacascudo wrote:
Pawel ,I tried to use damping through compatibles nodes or supports as a workaround for this problem , but it also didn´t work when nonlinear is choosen.It worked perfectly for Linear analysis
Yes, any kind of viscous damper (defined in releases, compatible nodes or in supports) does not work in case of nonlinear time history.
Rafacascudo wrote:Is there any other workaround to solve this problem , or for now , any kind of damping is incompatible with any kind of nonlinearity??
In such case it is possible to use distributed damping, defined using Alpha and Beta coefficients. It was suggested some time ago by Tuctas in his post.
Rafacascudo wrote:Was this always like that or it worked in any of the previous versions of the program??
It was always like this - since the implementation of viscous dampers in v.21 😞
Regards,
I'm unburrying this thread : what's new about that in RSA 2016 or RSA 2017? dampers + non linear THA is working?
Thx