Hi Mohammad,

To discuss it clearer can you answer the followed questions(?):

-what type of analysis are you implementing: Dynamic Explicit, Implicit or static?

-do you have any pre-strain/stretch definition in your model?

-is thermal loading included in your simulation?

Regards,

Hamid

Actually it's dynamic explicit analysis

initial strain all are zeros, and no thermal loading

when i do it as displacement control, i have considerable negative value, whereas load control just a small value

appreciating your help

What I believe is when you 1st apply the constraints to the model,

the moment you will start test, it will 1st collapse and  thus it gives the negative graph, however you can ignore them, since they are irrelevant to what happens in actual.

Hi, HAMID.

Sometimes when you are using displacements control only, you must care about its value. If it is possible, I recommended that firstly you begin the analysis with a little part of the load, so that nonzero but very thinny stiffness in some direction can be catched (I suppose that this can be some input data error, like mistyping, this can help you to find, if it does exist). Moreover, sometimes, even if the applied displacement can be in your judgement "little", this little is enough to promote some incorrect program procedure if the time integration is large. Mean, at the time you are integrating, the program catch the structure answer at a second stage, where instead of going down, it is going up, So look carefully at the time integration and the method addopted to do it. Sometimes in FEM, these considerations: displacement step, time step, integrating time, need to be very short for the mathematical answer be correct or acceptable. Try to change these parameters and also look to the formulation envolved. Some formulation require special care on that above 3 parameters and maybe others too.

I hope this can help you. Good luck!