question on Model builder

[derogar]

using model builder for a 2D problem,
model BasicBuilder -ndm 2 -ndf 3
which mean that we have trasfomation in X and Y direction and rotation in Z axis.
how the program knows that the third one is rotation in Z axis(direction 6)?

especially when we need to model rotational spring in direction 6?

[silvia]

direction 6 in 3D is direction 3 in 2D.
the stiffness matrix pretty much specifies what the directions are. this matrix comes from the elements. likely, you are using beam-column elements and in 2D they have 3Dof's at the nodes: 2 translations and one rotation.

[derogar]

Dear Silvia,

is this comment correct:
for modelling rotational spring, we need to tell the program direction 3 instead of 6, like:

element zeroLength 2 1 3 -mat 4 -dir 3



Another question is in the example of limit state material, Ken used 2D model and with " -ndm 2 -ndf 3" and for introducing zero length end springs for example he used the following:

element zeroLength 3 3 4 -mat $shearTag $axialFailTag centerSlipTag -dir 1 2 6
which means in 2D model he used direction 6 which is not correct.

Thanks
Shahram

[silvia]

unless the program defaults to something else, and unless he changes the model builder to ndf=6 -- yes, it is wrong!
I can only keep track of my own examples, sorry.