Rocking Behavior using Flat Slider Bearing Element

[AngusYang]

Hi,
I was trying to analyze a 2-story 1-bayX 1-bayY steel structure model with Flat Slider Bearing Element under a 2-way ground motion excitation. Due to the previous experiment on shaking table, there would be some significant uplift and rocking at the bearings, however, the output of the model did not show that. The displacement output at DOF 1 and 2 seems to be fine but at DOF 3 it just not right.

Here is the Flat Slider Bearing Element part of my code: (unit in kN-mm)

#base
fix 10 1 1 1 1 1 1
fix 20 1 1 1 1 1 1
fix 40 1 1 1 1 1 1
fix 50 1 1 1 1 1 1

(node 1 2 4 5 are the bottom of the columns, and all connected by beams.)

uniaxialMaterial ENT 2 10e+10
uniaxialMaterial Elastic 3 0.0

frictionModel Coulomb 1 0.2
element flatSliderBearing 10001 10 1 1 1 -P 2 -T 2 -My 3 -Mz 3 -orient 0 0 1 -1 0 0
element flatSliderBearing 10002 20 2 1 1 -P 2 -T 2 -My 3 -Mz 3 -orient 0 0 1 -1 0 0
element flatSliderBearing 10004 40 4 1 1 -P 2 -T 2 -My 3 -Mz 3 -orient 0 0 1 -1 0 0
element flatSliderBearing 10005 50 5 1 1 -P 2 -T 2 -My 3 -Mz 3 -orient 0 0 1 -1 0 0

I assumed that there would be no tension to constraint rocking and uplift, however it did not turn out like that.
Is there any advice or I should try some other element or method to release those nodes?

All the best
Thanks .

[selimgunay]

It could be that you have some gravity loading which the tension forces due to overturning do not overcome

[AngusYang]

Thanks for your advise! However, I tried reducing the gravity loads, there's no much difference.
I wondered if the Flat Slider Bearing Element constraints the nodes?

Or element zeroLengthSection, element zeroLengthContact3D, or any other element is more suitable in this case?
All the best
Thanks .