Max shear

[Jhno]

Hi,
I would like to obtain the maximum shear resistance of a section.
I started with the example for moment-rotation on the opensees wiki.

I simply modified the fix condition of the second node to allow for displacement in the direction 2. I fixed all other displacement and checked. Without even having any load pattern, the model fails.
I am not sure why it's not stable? When I fix dof #2 and unfix any other dof for node 2, the model goes fine.. but as soon as I unfix dof #2, it fails. Why?

model BasicBuilder -ndm 2 -ndf 3
node 1 0. 0.
node 2 0. 0.

fix 1 1 1 1
fix 2 1 0 1
section Elastic 1 200.e6 1. 1. (this isn't my section but it does just fine for the example.)
element zeroLengthSection 1 1 2 1

system SparseGeneral -piv
test NormUnbalance 1.e-3 10
numberer Plain
constraints Plain
integrator LoadControl 1
algorithm Newton
analysis Static
analyze 1

This will fails.
when using fix condition like this instead
fix 1 1 1 1
fix 2 1 1 0
It works..as long as dof #2 isn't free. Why does this happen?

I am thinking about simply swtiching the section upside down so I can simply fix dof#2 and unfix #1 but I still wonder what is going on?

[EricsonEncinaZ]

Because you are using a zero-lenght element which is fibre-based, and therefore it captures axial and bending but not shear. In other words it needs a shear restrain, otherwise you have a mechanism. You can provide that by either fixing that DOF or by aggregating a stiff material to represent the shear behaviour. Similar reponse here http://opensees.berkeley.edu/community/ ... =2&t=64453

[Jhno]

Ah, thanks alot again !