geometric transformation in 3d building model

[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. That the thing you told me is quite different. and now I am again confused what should I do.
Sorry to bother you.

[AHARSHIAN]

Hi,
Consider: Global X to the right, Global Y to the up and Global Z is out of plane!
Now, Consider a beam element. The local x axis is along the length of the element which is Global X axis. The local y and local z axes could rotate based on right-hand-rule! For example: local y upward (Like Global Y) and local z, out of plane (Like Global Z). Therefore; Because the local z is exactly in direction of Global Z: The transformation will be: 0 0 1.
If for example you have considered local y in Global Z direction, then local z SHOULD be in Negative Global Y direction (Right - hand - rule!). Therefore; the linear transformation will be: 0 -1 0.
Therefore; definition of local axes is on you! then look at local z and find it's direction compare to the Global Axes.
What I said before is exactly what I am saying now.

[shivanirani11]

Thank you very much,

Just there is one more thing that can I assume different orientation for local axis in the same frame.

[timbright116]

So that's how it works, I think i was using z-axis as x-axis.
Ahhhh.......... damn wasted a lot of time.

[AHARSHIAN]

To shiveanirani11:
Yes, you can assume different orientation of local axes for each structural component! But it will be very complicated since you have to define the transformation for all structural components individually! It is recommended to use one geometric transformation for all Columns, one for all Beams and one for all Girders.

[shivanirani11]

Thanks Aharshian,

You help me a lot. I will try it as you say. Can you give me your mailID for further contact

[soraya]

Hi all,
I want to model a 3D steel braced building with concentric X bracing in both directions.
I am defining beams in X direction, Girders in Z direction and columns in Y direction.

I have problem for defining transformation of bracing elements.

geomTransf Linear $IDbrace45degreeXdir 0 0 -1;
geomTransf Linear $IDbrace135degreeXdir 0 0 1;
geomTransf Linear $IDbrace45degreeZdir -1 0 0;
geomTransf Linear $IDbrace135degreeZdir 1 0 0;

Are these correct?