Extract fixity condition of nodes

[gopaladhikari]

Hi all,

I am wondering whether I can extract information about the fixity condition of nodes from an analysis model, similar to node mass (nodeMass(nodeTag)).

https://openseespydoc.readthedocs.io/en ... eMass.html

Thanks,
Gopal

[mhscott]

You can use nodeDOF and the DOFs with -1 are fixed.

[gopaladhikari]

Hello,

Thanks Prof Scott. I tried with nodeDOFs(nodeTag). Below is a part of my code.

Code: Select all

ops.fix(1, 1, 1, 1, 1, 1, 1)
print(ops.nodeDOFs(1))

This outputs

Code: Select all

WARNING nodeDOFs DOF group null
opensees.OpenSeesError: See stderr output

[mhscott]

Ahh, you have to do it after an analysis. The equation numbers aren't assigned until the analysis starts.

[gopaladhikari]

Thanks Professor Scott.

[gopaladhikari]

Hello again,

I am modelling a SSPquadUP element. Bottom nodes are fixed for displacement and top nodes are fixed for pore pressure only.

Code: Select all

ops.fix(1, 1, 1, 0)
ops.fix(2, 1, 1, 0)  
ops.fix(3, 0, 0, 1)  
ops.fix(4, 0, 0, 1)

When I requested nodeDOF for all nodes, I got this output, as expected.

Code: Select all

[-1, -1, 5] [-1, -1, 4] [2, 3, -1] [0, 1, -1] 

When I introduced equalDOF at the top nodes as below,

Code: Select all

ops.equalDOF(4, 3, 1, 2)

I got completely different node fixities.

Code: Select all

[-1, -1, 3] [-1, -1, 2] [-1, 0, 1] [0, 1, -1]

The fixity apparently changed for Node 3 and 4. DoF 1 of Node 3 and DoF 3 of Node 4 are now fixed.
When I changed the order of nodes, I got the similar results.

Code: Select all

[-1, -1, 3] [-1, -1, 2] [0, 1, -1] [-1, 0, 1]

Am I missing something here?
Is there any guidance available how DoF numbering varies with the selected Constraint Handler. Note that I used Transformation constraint handler. Any advice is greatly appreciated.

[mhscott]

Frank explained this to me a couple weeks ago, but I didn't write it down! I think the issue is the DOFs are reordered at the constrained nodes. Instead of 1,2,3 it's retained followed by constrained, so 2,3,1. Thanks for the reminder, I'll have to write a post about it