Linear Transformation

[shivanirani11]

Hello,

Can you please tell me how to use linear transformation command for 3D analysis. I have already tried to understand it form the mannul as well as form the opensees site. But I not able to understand it properly. Can you please tell me in a best simple way.

[vesna]

By using a geometric transformation you need to define a local coordinate system for your element. Local x axis always goes along the element (from node i to node j). With "geomTransf " you need to define local z axis.

[shivanirani11]

I am facing one more problem in linear transformation that at the site , vecxz is taken as parallel to x-z plane in the direction of z-axis and in the mannual it is taken as opposite to the direction of z-axis which one is correct. Please tell me

[vesna]

when talking about axes always mention if it is local or global. can you rewrite your question using these attributes.

[shivanirani11]

Actually I am just saying that the details given for reference in the manual of opensees and on the site for the same problem are different. So I am little bit confused which one should I refer. Till now I am just trying how to use this command.

[vesna]

I looked at them and I do not think they are different.

[shivanirani11]

Soorry to bother you.
I have the pdf file of the mannul of the opensees. So in that manual there is a difference in defining the vecxz from the command manual of the opensees site. Now, I think so that after deciding the x-z plane, the vecxz will be described by taking a vector along the direction of z-axis in the global vectors.

[vesna]

Yes, you are right.

[shivanirani11]

can you tell me that how to decide the local coordinate system. I thing that for the local coordinates, firstly I have to fix x-axis along the element and then using the right hand rule I can fix the other axis. But after talking to one friend, member of opensees, That the thing he told me is quite different. and now I am again confused what should I do.

[vesna]

Yes, local x axis always goes along the element length. Use right-hand rule to fix the other two axis. After you fix the y and z local axes make sure to define your section or element properties relative to these local axes.

[rasoulazadi]

hi dear vesna
i for determination of local axis act as follow :
The x-axis is the axis connecting the two element nodes
then i consider y axis optional
then using the right hand rule i determine z axis
then the vecxz is the vector that its direction is the opposite direction of z axis
is that true
please help me
best regards

[gerber]

no ! actually the vector xz has the direction of the local z axis. So, you just notice the connection between local and global z axis and that`s how you define the transformation...