MultiSupport Excitation vs Uniform Excitation

[Tortuga]

Hello all,
I have been working on a 2D reinforced concrete frame model with concentrated plasticity hinges at the ends of every member. The concentrated plasticity springs are modeled using the 'Hystertic' material.

I have been working on verifying that the uniform excitation pattern generates the same results as using the multisupport excitation pattern when each pattern is using the same earthquake. However, I am not able to get the same results as anticipated. I have compared these models to the examples, but my results are still not lining up correctly, but the magnitude and periods of the results are very close to eachother.

Can anyone please help me determine potential causes of error?

Thanks

[mhscott]

Not really sure which results you're looking at, but multi-support uses total acceleration while uniform excitation uses relative acceleration:

https://portwooddigital.com/2021/08/29/ ... xcitation/

[Tortuga]

Thanks mhscott, to clarify, by "results" i mean that I am measuring the lateral drift of a reinforced concrete portal frame using two identical models - one with uniform excitation and the other with multisupport excitation. I have found that when I use Rayleigh damping command with only the betaKcomm value, the top displacement line up *nearly* perfectly. For some reason, once the multi support model input values end, the displacement mysteriously increases unexpectedly.

However, when I input alphaM and betaK values for the damping characteristics, they no longer match each other as well. In both models they have the same values for alphaM, betaK, and betaKcomm. I have linked to a file below that hopefully illustrates my dilemma. Let me know if the link doesn't work.

https://drive.google.com/file/d/1PYORzv ... sp=sharing

Said another way, I have two problems:
1) Why do the two different models not have the same results when they have the same damping characteristics (betaKcomm)?
2) why does the multi support excitation model (and only this model) have a sudden jump after the last input value?

Thanks to everyone for their help!