difference between Basic and Local Coordinate system?

[yangct]

Hello everyone!
I'm using the element recorder of twoNodeLink element and 'force,' 'localForce,' 'basicForce,' 'localDisplacement,' 'basicDisplacement' are available for this element.
I want to record the displacement and force of the i and j nodes of the twoNodeLink element, which option is proper?
It looks that when I choose the localForce and localDisplacement, the results were desirable. But I don't know whether that's right.
What's the difference between the Basic Coordinate system and the Local Coordinate system?

Thank you!

[emjac]

It is hard to explain this without a schema. Take a look at this: https://goo.gl/photos/NXLwGy7maGVX16Y7A

If your element's x-axis is parallel to the global x-axis then local and global displacements are the same, if not be careful that you know which one you are recording.

[yangct]

emjac wrote:
> It is hard to explain this without a schema. Take a look at this:
> https://goo.gl/photos/NXLwGy7maGVX16Y7A
>
> If your element's x-axis is parallel to the global x-axis then local and
> global displacements are the same, if not be careful that you know which
> one you are recording.

Thanks for your help emjac!
But I know the concept of local and global coordinate system.
What I'm wondering now is the definition of BASIC coordinate system.
Because when I use 'recorder Element localForce' and 'recorder Element basicForce' , I got different outputs.

[emjac]

Ah sorry. I read your post quickly. Look here.. she gives a quick description: http://opensees.berkeley.edu/community/ ... rce#p42683

and also here for a longer description : http://opensees.berkeley.edu/wiki/image ... EvsDBE.pdf

[yangct]

emjac wrote:
> Ah sorry. I read your post quickly. Look here.. she gives a quick
> description:
> http://opensees.berkeley.edu/community/ ... rce#p42683
>
> and also here for a longer description :
> http://opensees.berkeley.edu/wiki/image ... EvsDBE.pdf


Thanks a lot!

If I want to extract the Force-Displacement relationship of the two ends of a certain beam or column in the whole structure model, use recorder basicDisplacement and basicForce. Is this right?

[emjac]

I have not used it myself, but I would interpret it that way ie. the displacement should be relative... but I would test it first!