P-Delta Effects for Models With Elements which doesn't include Geometric Transformation

[HajMaf]

I have Modelled a Modular building in Opensees. This Includes Boxes( Modules-made of shell elements) connected with two node link elements to form a building as shown below.

We also developed an experimental model of the same and noticed the results for the top displacement.
I could notice that there is a shift (shifting upward) of the baseline in the experimental results which i believe is due to the P-delta effects while the experimental results, top displacement base line was on Y=0 line, i.e X axis. Also i can see that my Opensees Model has no way of getting P-delta effects activated because Neither two node link element nor the shell elements used to model the boxes have coordinate transformation feature.

May i please get your idea on this? how can i let my Opensees model take in to account the P-delta effects? is there any other way to account for that? Or is it not the P-delta effects that's causing the shift of the base line?

I tried adding a leaner column, but it wasn't successful. i followed the exact procedure mentioned for that on Opensees website. But the eigenvalues were imaginary.

[selimgunay]

For this case, leaning column is the only option to consider p-delta effects. Imaginary eigenvalue can be because the leaning column itself is unstable as it has a hinge at the bottom and connected to only axial trusses. Did you assign masses to the leaning column ?

[HajMaf]

Hi Yes, i assigned masses to the leaning column. But still i keep getting imaginary Eigenvalues. IS the leaning column method valid for 3D models as well? mine is a 3d Model, but i assigned a leaning column to the first frame of the building only.

"Imaginary eigenvalue can be because the leaning column itself is unstable as it has a hinge at the bottom and connected to only axial trusses" if this is the case, what do you recommend to solve this issue?