Stiffness in the M2 DOF

[mel]

Hello,

I am trying to model a steel panel zone by having rigid elements (1m x 1m) as a rectangular perimeter and then a diagonal element connecting the opposite corners of the perimeter. The diagonal member is broken into two parts and a spring with only axial stiffness is added where the two parts of the diagonal meet. All the corners have hinges on them and thus if there is lateral loading, a mechanism should form. My problem is, if I don't have any stiffness in the M2 DOF the program won't run, and if I add stiffness in the M2 DOF, it causes moments to form where there shouldn't be any.

I have already forced my diagonal members to have 0 bending by enforcing large widths and small depths, but I still get moments cause I am forced to have M2 DOF stiffness.

Do you have any suggestions as to avoid this problem?

[seismosoft]

Hi,

Have you tried to assign a very small non-zero stiffness (not "0" but rather "1" or "10")? Would this do the trick?

Seismosoft Support

[mel]

Hi, thanks for your previous reply. I have tried what was suggested. For the most part it works. However, When I need to utilize a linear-asymmetric link, the F3 DOF needs to be about 60kN/m and the M2 about 50. I want to create a spring that is completely rigid when compressed, and 0 stiffness when stretched. Any suggestions as to what the problem could be? 60kN/m is way too high for what I am trying to achieve.
Thanks

[seismosoft]

Hi,
- you can try using a hook/gap curve
- make sure that your structure can cope with the zero stiffness, from a static equilibrium viewpoint
Regards,
Seismosoft Support