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.
"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?