The OpenSees Community

Try dividing your column into two segments and moving the midnode sideways for initial imperfection. For details, you can refer to Uriz et al.

Uriz P., Filippou F., and Mahin S., “Model for cyclic inelastic buckling of steel braces”, ASCE Journal of Structural Engineering, 134(4), 619-628, 2008.

i am not sure but you can try to assign negligible (1.e-20) masses at non-mass joints.
You may know similar problem happens with eigen command,
as i said, not sure, but may figure it out

globalForce 2D, 3dof: FX FY MZ
localForce 2D, 3dof: Fx Fy Mz
X,Y and Z for global coordinates
x,y and z for local coordinate system of members
for your columns, if you use localForce recorder that Fx will be axial load
since you include -time expression than 2nd column will be axial load

I am sorry but i couldn't figure it out
by the way, application of lateral load at both exterior nodes (node 9 and node 41) would be more accurate approach

Dear ysir,

I can't see where the problem is
if you send your script, hopefully i help you

For simple connection, you need to use zerolength elements and equalDOF command between different nodes at same coordinates
there is a example about it
opensees.berkeley.edu/community/viewtopic.php?t=16686

you may refer to "Model for Cyclic Inelastic Buckling of Steel Braces" by Patxi Uriz; Filip C. Filippou; and Stephen A. Mahin

I hope it helps

Do you use the command "model BasicBuilder -ndm $ndm" at the beginning of the script?

Instead of "pattern Plain 1 Constant"
you should use "pattern Plain 1 Linear"

by the way
"-eleload" command is problematical with corotational formulation

i hope this helps you

I forgot to say
For braces, you need to use corrotational transformation and use fiber section to account for moment axial load interaction.

Hi Zephyre; You need to use equalDOF command for pin connection. First assign slave nodes to where braces are connected to other members so master and slave nodes have same coordinates then use equalDOF command to achieve same DOFs in x and y direction between master nodes and slave nodes (not in z ...

Hi Dr. Silvia; I need to use pinned connections in 2D frame system To achieve that; I assign two nodes with different node tags and with same coordinates, after I use equalDOF command for x and y directions. The problem is after completing analysis, the deformations in x-direction are different (for...

I figured it out.

Thank you for your precious help, Dr Mazzoni

According to the paper "Model for Cyclic Inelastic Buckling of Steel Braces" Patxi Uriz; Filip C. Filippou; and Stephen A. Mahin to represent buckling behaviour, I am using nonlinear beam-column element for braces so I can't use truss element for braces I used infinite small length elastic...

Hi; I want to model a pin for brace connection in a 2D frame As far as I know I need to use Zero-Length Element with a low stiffness elastic material and equalDOF constraint My question is that how i can define the orientation of the local axis of the brace ? I am confused with the explanation in th...