Hi,
I have tried to make a non-linear analysis (geometric deformations) for a "large" structure (20772 nodes with bars, plates etc) and the results are suspicious.
I used first the incremental algorithm and I got minor bending moments than the linear analysis..
I changed to the Arc-length (poor documented...) the results were better or more logic.
I used first 5 load increment steeps. The results: Internal forces 20% higher than the lineal analysis but also the applied loads were 20% higher (from the reactions table results).
Where do this loads come from???? I have used the same load all the time!
Then I used 10 load steeps and got 10% higher internal forces and applied loads.
30 steeps; 3% higher
50 steeps; 2%
100 steeps almost the same than the lineal.
If you don't have notice the ROBOT algorithm for 2nd order analysis seems to be:
Results_2nd_order = Results_1s_order x [1 + 1/ (load steeps)]
I have even read in a doctoral thesis that "ROBOT cannot perform analysis of second order att all".
Some body know better than me about this subject?