Moments appearing in the wrong plane

[OmarA]

Dear STKO team,

I created a model in openseespy and I am trying to visualise the gravity results in STKO but I am a bit confused.

The orientation of the beam in Global X and Global Y is made using the following commands:
op.geomTransf(BTransfType, BTransfTagX, 0, -1, 0, "-jntOffset", *dI, *dJ)# local z-axis is in the negative global Y-axis
op.geomTransf(BTransfType, BTransfTagY, 1, 0, 0, "-jntOffset", *dI, *dJ)# local z-axis is in the positive global X-axis

and when I plot the local axes they seem to be right as shown here:

Screenshot 2024-09-16 at 8.42.18 PM.png (270.29 KiB) Viewed 3215 times

I defined the uniform gravity load using the following command:
op.eleLoad("-ele", eleID, "-type", "-beamUniform", -WyX, 0.)

No when I run the model and open the .mpco file and create a beam diagram plot. The results of the section.force Mz is as shown here:

Screenshot 2024-09-16 at 9.02.13 PM.png (432.92 KiB) Viewed 3213 times

Shouldn't the Mz be the moment around the local z axis? so the diagram should be plot in the X-Z plane not the X-Y plane?

Thanks in advance.

[kesavapraba]

Hi, the script seems to be fine, however the directions (in RGB Red, Green, Blue) in the first figure is not aligned with what is shown in STKO coordinate systems. For example, the local-x axis (red) should be oriented along the length of the beam, this is not correct in your first figure.

[OmarA]

Hey Kesavan,

Thanks for your reply.

The axes shown in the first figure are the local axes while the axes shown in stko are the global axes.

If the red is the X-axis in stko and the green is Y-axis then the global axes match between opensees and stko as shown bellow:

Screenshot 2024-09-20 at 2.11.54 PM.png (162.77 KiB) Viewed 3117 times

Please note that I think opensees uses different colour convention. GBR in opsvis are the X, Y and Z, respectively.

[kesavapraba]

You are welcome. Noted your points with thanks.

[STKO Team]

It's probably because you did not create the model in STKO pre processor.
Local axes are not obtained as an output from Opensees (they are not available for all elements), so we use STKO to generate a support file for the mpco recorderer, with the extension .mpco.cdata.
It contains several information not available from opensees recorder such as local axes and section extrusions

[OmarA]

It's probably because you did not create the model in STKO pre processor.
Local axes are not obtained as an output from Opensees (they are not available for all elements), so we use STKO to generate a support file for the mpco recorderer, with the extension .mpco.cdata.
It contains several information not available from opensees recorder such as local axes and section extrusions

Thanks STKO team for the reply. Is there a way to change the local axis direction in the .mpco.cdata? or any other solution?

Thanks in advance.

[STKO Team]

If you are not using STKO as a pre-processor, you don't have an mpco.cdata file associated with your mpco file.
However you can write an mpco.cdata file with the information of the local axis if you want.
But you need to understand how it works and there is no documentation about it (it's built by STKO, and not meant to be written by the user)

Try to create a sample model in STKO, write the input files and try to understand where the local axis information is written.
Then you have to figure out how STKO writes it (and you need to lear how Quaternion work!)