Uniform Excitation/ MultipleSupport Pattern

[jpereirasan]

Good morning STKO team.

In an excel spreadsheet, how can I get the total displacement on a node that was excited using UniformExcitation? I have to add all the displacements of the node and the total corresponds to the displacement?

If I am using the groundmotion command and multiplesupport pattern, I want to apply some accelerations in x to a node that is already constrained in x, should I use the removesp constraints command so that the other nodes of the model can move in that direction?

[STKO Team]

In an excel spreadsheet, how can I get the total displacement on a node that was excited using UniformExcitation? I have to add all the displacements of the node and the total corresponds to the displacement?

You have to add the displacement of the ground (i.e. the displacement obtained from the ground motion acceleration).

If I am using the groundmotion command and multiplesupport pattern, I want to apply some accelerations in x to a node that is already constrained in x, should I use the removesp constraints command so that the other nodes of the model can move in that direction?

When you impose a multisupport excitation to a node, OpenSees will apply an imposed displacement to that node. If you use a transformation constraint handler, it is not necessary to remove the old fix, as the new one replaces the old one.
Instead, if you use the Penalty handler, you must remove the old one, otherwise, you will have 2 "penalty springs": one that wants to keep the node fixed at zero, and the other that wants to displace the node, and the results will be the average

[jpereirasan]

Thank you very much for your answers, they are very helpful.
I would like if you can help me with these doubts.

1)If I want to model a container whose edges do not move, but I want to apply a series of accelerations in the base I can do it with MultipleSupport Pattern? or this implies that those nodes of the base that are already fixed will suffer a displacement?

2)What is the difference between applying a timeseries with MultipleSupportPattern or applying a series of displacements with sp displacement and plain load pattern ?

[STKO Team]

1)If I want to model a container whose edges do not move, but I want to apply a series of accelerations in the base I can do it with MultipleSupport Pattern? or this implies that those nodes of the base that are already fixed will suffer a displacement?

Sorry but I don't understand this point, can you elaborate it?

2)What is the difference between applying a timeseries with MultipleSupportPattern or applying a series of displacements with sp displacement and plain load pattern ?
It's the same, but the MultipleSupportPattern also imposed velocity and acceleration

[jpereirasan]

Thank you very much for your answers.
About how to process the data obtained with UniformExcitation.
I understand that
For the displacements I must integrate twice the accelerations time series I am using as input and then I must add it to the displacement recorded in the node I want to calculate.
I understand that the accelerations and pore pressures are absolute values and I should not do any additional work.
Am I correct?

[STKO Team]

For the displacements I must integrate twice the accelerations time series I am using as input and then I must add it to the displacement recorded in the node I want to calculate.

Yes

I understand that the accelerations and pore pressures are absolute values and I should not do any additional work.

Acceleration velocity and displacements are all relative (in fact in the fixed node they will be zero).
Not sure about the pore pressure, because the uniform excitation should not work on it.
Anyway you can do a simple test to assess it

[jpereirasan]

Hi STKO Team. Thanks for your reply.

I have been working on post-processing the results, as I told you using UniformExcitation.
But the results do not follow as expected even using the same properties, elements, input accelerations and analysis steps as the reference.
I am adding the displacement at each time step obtained from STKO with the displacement at that time step of the input register.
Could you check if I am correct?

[STKO Team]

That's because the integrated displacement can contain rigid body translation.
However, looking at the image called TARGET (in your excel) it seems they are using relative displacement as well (it's zero at the bottom). Please double check it