Defining a Riks, static step

[SofiaB]

Hello everyone,
I am analyzing a steel SHS truss, with am applied displacement at the tip. The truss displacement is laterally constrained and in that same sections, springs were modelled to simulate the fact that in a previous experimental test the lateral constraining system was at a certain distance from the truss. What I want to achieve is the load-displacement curve at the point where the displacement was applied.

Since I want to include nonlinearity in the model the step I used was RIKS, static. But I also analysed the model with a General, static step and came to the conclusion that for the same applied displacement and a maximum number of increments, the truss where a general step was used presented a bigger vertical displacement, which I also want to achieve through a Riks step. Did this happen because of the way I modelled the Riks step?

I will leave some images for a better understanding.
Thanks in advance!

 

[FEA way]

In the case of Riks analysis it's important when the analysis ends. By default it runs for the number of increments specified as maximum but you can also define stopping criteria (max LPF or max displacement at a selected DOF). In this case you may have to increase the maximum number of increments for Riks step or use stopping criteria to reach higher displacement.

 

[SofiaB]

The problem I am facing is even though the stopping criteria is 400 mm at the point where the displacement is applied, the force and displacement stop before and the results for the following steps are constant( meaning there is no more increase of force and displacement even though the analysis continues to run).

 

[FEA way]

Are imperfections used in this analysis ? Properly scaled imperfections may have significant impact on the completeness and correctness of the solution.

 

[SofiaB]

No, I am not using any imperfections since the maximum force corresponds to the one obtained in a previous experimental test.