Hystersis curve for FPS bearing

[engnomran]

Hi dear all
I have 1 question about hystersis curve for FPS bearing.
I model FPS bearing with codes( TestSlider2d_0.tcl models a rigid isolated mass and the bearing element has zero length.) in site opensees.
I draw hystersis curve for FPS bearing for two diffrent dt in Matlab.
I analyze FPS bearing for bidirectional(Horizental and Vertical ,2D).
I decrease dt(step analyze),why top and bottom hystersis curve change ?(I show in under pictures)
dt earthquake = 0.01

I put pictures of hystersis curves in under.
Two dt for 1 earthquake and 1 isolator(FPS bearing).

1-dt=0.01
analyze $npts 0.01
http://upload7.ir/imgs/2014-07/36149637449745261673.jpg

2-dt=0.0001
analyze $npts 0.0001
http://upload7.ir/imgs/2014-07/76366734815057476883.jpg



thanks.

[maksins]

What I understand is that when you decrease your time step, you increase the resolution and hence the maximum frequency that you can capture in your response. Since your shear force is dependent on the axial force, you capture high frequency oscillations when you decrease the time-step.
If you remove vertical excitation, and you don't see fluctuations any more, it must be due to above reason.

[engnomran]

Hi
thanks a lot of you
I knew, vertical motion change top and bottom hystersis curve but I say earthquake' records which does not change Uniformly therefore top and bottom hystersis curve shouldnot change Uniformly

I zoom in hystersis curve for FPS bearing.

http://upload7.ir/imgs/2014-07/69933710467620162603.jpg

Why does hystersis curve change Uniformly?

Why does hystersis curve is correct ?

thanks