Applying Earthquake Motion to each node at model bottom separately

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youngkyu
Posts: 36
Joined: Tue May 04, 2021 3:36 pm

Applying Earthquake Motion to each node at model bottom separately

Post by youngkyu » Mon Aug 02, 2021 5:12 am

Dear support member,

I have a quick question about the boundary condition applying earthquake time series to model bottom for modeling seismic geotechnical structures (i.g., square/rectangle sites, slope, retaining structures or shallow foundation etc.)

I believe that, in STKO, we can put earthquake time series (acceleration or velocity) to each node at model bottom individually with an time interval (e.g., sampling rate of the record).

As shown in the attached figure,
I want to give the entire time series to the first node at time = 0 sec, and then
do it to the second node at time = dt sec (e.g., 0.01sec which stands for sampling rate of time series), and then
do it to the third node at time = 2xdt sec so on till by the last node on the right side of model bottom.
(In other words, the ground shaking at the first node starts at t = 0 sec and
the ground shaking at the second node starts at t = 0.01 sec and
the ground shaking at the third node starts at t = 0.02 sec so on)

This means (you may recognize my purpose) that
I want to simulate the inclined wave propagation within OpenSees.
(This may be referred as 'moving node' for entering earthquake record).

This can be done by python-API (PyMpc), right?
I would like to have some comments or tips for achieving this task from you.

Best,
Youngkyu
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STKO Team
Posts: 707
Joined: Tue Oct 29, 2019 8:45 am

Re: Applying Earthquake Motion to each node at model bottom separately

Post by STKO Team » Mon Aug 23, 2021 10:51 am

Dear user,

I understand your purpose. Probably it's easier if you do it with a customCommand using TCL commands.
However, it is not going to be easy.

I would start creating a region in STKO with all the bottom edges. In this region you can tell STKO to write a TCL list, so that you can access the nodal tags in TCL from that list.

Then you need to sort them according to their X coordinate (you can use the nodeCoord opensees command).

Then you need to create a custom procedure that, after each analysis step, adds a new groundMotion to the node according to the current time.

You can try to play with it, and if you have issue let us know.


Keep in mind that you will have many issues.. first is that if you use GroundMotion, you are going to have reflections. If instead you use absorbing boundary contions, they do not work well for inclined waves...

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