Partial Fixity

[easap]

Hi guys

I have a problem with the partial fixity properties of frame elements when performing a modal analysis. There is no problem if working with 2D frame systems. However, when the system is three-dimensional, I am not able to define partial fixity for moment 22 while moment 33 is fully released and the other way around. When performing a modal analysis with one direction partly fixed and one fully released, the mode shapes and natural frequencies are as if no partial fixity exists at all.

The model I am working on can be seen below. I would like to have a partial fixity for M22 where the horizontal elements connect to the two inclined elements.

I experience the same problem when trying to assign joint springs.

Hope somebody can help..

 

[johnbridge231]

Can you upload your model?

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html

 

[easap]

Sure,Link

 

[IJR]

You are probably using a nonlinear element to model your partial fixity.

But modal analysis is linear.

hope this helps

 

[easap]

Is it not possible to use partial fixities when performing a linear modal or time-history analysis?

 

[johnbridge231]

Yes of course, partial fixitis are pure-linear things.

Analysis and Design of arbitrary cross sections
Reinforcement design to all major codes
Moment Curvature analysis

http://www.engissol.com/cross-section-analysis-design.html