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Hello,everyone! I can define the vertical mass and stiffness to get the vertical frequency,but during the timehistory analysis, horizontal and vertical mass and stiffness need to be appended at the same time to simulate the real reaction of structure, so the problem is coming, after time history analysis, how to stay the state(structural damage) and get the vertical frequency?
I can not delete the horizontal mass and stiffness and get the vertical frequency because doing that will cause time history analysis results loss, only get the original vertical frequency of structure.
Thanks for your answers!

mhscott wrote: ↑Tue Apr 16, 2024 4:53 am The modes dictate which directions get the target damping ratios. All the other modes get whatever according to the damping spectrum.

In fact,I'm not sure about it.If I define the stiffness and mass in both horizontal and vertical direction,then I use the sentences that what I have posted,I will get same damping ratio in both horizontal and vertical direction?

Hello,I met a question about Rayleigh damping,I used following sentences to define the damping,but it seems like only define the horizontal damping ratio.
set xDamp 0.05;
set nEigenI 1;
set nEigenJ 2;
set lambdaN [eigen [expr $nEigenJ]];
set lambdaI [lindex $lambdaN [expr $nEigenI-1]];
set lambdaJ [lindex $lambdaN [expr $nEigenJ-1]];
set omegaI [expr pow($lambdaI,0.5)];
set omegaJ [expr pow($lambdaJ,0.5)];
set alphaM [expr $xDamp*(2*$omegaI*$omegaJ)/($omegaI+$omegaJ)];
set betaKcurr [expr 2.*$xDamp/($omegaI+$omegaJ)];
rayleigh $alphaM $betaKcurr 0 0
I want to define 5% damping ratio in vertical direction,how can I achieve it?Thanks a lot for your reply!

Thanks for your reply！

Hi，everyone.I have a problem,I know that there are commands to output horizontal period/eigenvalue/frequency. Is there a way to output vertical frequency/period or vertical eigenvalue in OpenSees?
set xDamp 0.05;
set nEigenI 1;
set nEigenJ 2;
set lambdaN [eigen [expr $nEigenJ]];
set lambdaI [lindex $lambdaN [expr $nEigenI-1]];
set lambdaJ [lindex $lambdaN [expr $nEigenJ-1]];
set omegaI [expr pow($lambdaI,0.5)];
set omegaJ [expr pow($lambdaJ,0.5)];
set alphaM [expr $xDamp*(2*$omegaI*$omegaJ)/($omegaI+$omegaJ)];
set betaKcurr [expr 2.*$xDamp/($omegaI+$omegaJ)];
rayleigh $alphaM $betaKcurr 0 0
set numModes 12
set lambda [eigen $numModes]
set period "Periods.txt"
set Periods [open $period "w"]
puts $Periods " $lambda"
close $Periods
record (We can use the above command to output the horizontal eigenvalue/period/frequency of the structure)

But how can we output vertical eigenvalue/period/frequency in OpenSees？
Thanks for your reply,believe the answers will help more people who are confused about that.