Bi-directional Imperfection for second order anysis

Hi all, I hope you are doing well.

I am trying to perform a second order analysis in a tied arch steel structure by taking into account the imperfections both in plane and out of plane. I have assigned the imperfections from 2 eigen shapes (lc 111, 117) but i am not sure if the results are ok because the 2nd order internal forces are smaller than the 1st order.
Below is the teddy code i have used

+PROG ASE
CTRL OPT SOLV VAL - $ Solution of the system
SYST PROB TH2 ITER 60
OBLI LC 117 VMAX 0.525
LC 3020 DLZ 1E-10
END

+PROG ASE
CTRL CABLE 0
CTRL ITER 3
CTRL OPT SOLV VAL - $ Solution of the system
SYST PROB TH2 PLC 3020 ITER 60
OBLI LC 111 VMAX 0.472
LC 3021 DLZ 1.00
END

Best regards,
Alex

Hi Alex,
I don’t think your input with two consecutive modules will work. you need a stressless deformation of the structure before starting the geometric nonlinear analysis.
Plese note, the command OBLI can be used only once. In your case you need to create an imperfection loadcase with both imperfection in plane and out of plane.
In PROG SOFiLOAD you may use the free line loads, LINE, and the load types uy, uz, uys, uzs representing imperfections.
If you use SOFiPLUS as a graphical preprocessor, you are able to use this load types also. For different shapes it can be usefull to split the structure lines representing the arch, to have a simple access to the elements for a simple load definition.

Hope that helps