Hi,
I'm modeling thin-walled column under axial loading and horizontal displacement as shown in attachment 1 using displacement control (Boundary conditions). I decide and input the horizontal displacement to be as follows 125,-125, and 150.
1- If I create Amplitude as shown in attachment 2, I'll not get the exact horizontal displacements as shown in attachment 3 (Green line with U-F_δ/δy =10_Short title, instead of getting -125, I got -112.455) except the last point I'll get 150.
2- But, If I create 3 steps for cyclic loading with 125,-125, and 150, I'll get the exact input values as shown in attachment 3 (Black dashed-line U-F_δ/δy =10_ 3 push title). I cannot follow the second method for huge modeling. I've run many trials to make sure about my notice, same results.
Could anybody tell me why there is a difference?
the difference comes from automatic increment size when it is used with cyclic amplitude. we had same problem as you have and we solved as you mensioned by creat step correspond to each stage of cyclic amplitude.
you also can try to perform quasi static analysis using dynamic explicit with cyclic amplitude in one step. since the increment size is very small in dynamic explicit you will get a very good results compared to many static general steps (as you desired).
good luck
Really, i have the same conflict, thanks Raafat E S Ismail for clarifying.
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