You understand perfectly my point that 50% strain on the structure, which is equal to a 25 mm displacement of the top, might create a material strain in the ribs of some smaller value, but once the material strain has exceeded the rupture strain, the model is no longer predicting reality.
1. If you can find a material with a larger Elongation at Break (rupture strain), and ideally use the stress-strain curve for that material, then you can use the plasticity material model and if total strain is < elongation, then the computed Reaction Force will be valid for the 50% strain on the structure.
2. If you stay with a material with a low elongation and want to simulate the post fracture behavior, that can be done in ANSYS but it is complicated in Static Structural. One approach is to move the model into Explicit Dynamics which has element failure built into the solver by default. The down side is the extremely long solution times.