Nonlinear MPC184 - lead core elastomeric bearings

[struppige]

Hello.
I've been trying for a couple of days to model a nonlinear behaviour for the MPC184 elements. I've done a simple model to be able to simply verify the results by hand calculation (the stifness is linear and equal to 1000, but it is introduced like a nonlinear bearing, with TBPT). The model works, but the results aren't consistent with what I wanted to model.

Horizontal force: 2000
2 linear bearings, each with 1000 stifness; total stifness: 2000
The displacement should be exactly 1.

I have noticed that all my results (even if I change the force) are exactly 66.66667 times smaller. I must be missing something.
Thanks for your help in advance.

The script for the model is:

/PREP7

N,1,0,0,11
N,2,10,0,11
N,3,25,0,11
N,4,35,0,11
N,5,10,0,10
N,6,25,0,10
N,7,10,0,0
N,8,25,0,0

!!!!! ELEMENTS !!!!!
ET,1,MPC184,16,,,1 ! MPC184 element - General formulation - Displacements only
ET,2,BEAM188

!!!!! MATERIALS !!!!!
! Translation DOF stiffness (UX,UY,UZ)
TB,JOIN,1,,2,JNS1
TBPT,,0,0
TBPT,,1,1E3
TB,JOIN,1,,2,JNS2
TBPT,,0,0
TBPT,,1,1E3
TB,JOIN,1,,2,JNS3
TBPT,,0,0
TBPT,,1,1E3
! Material pentru BEAM188
MP,EX,2,1E10

!!!!! SECTIONS !!!!!
! Section for MPC184 - General joint
LOCAL,11,0
SECTYPE,1,JOIN,GENE
SECJOINT,LSYS,11
! Very rigid beam
SECTYPE,2,BEAM,RECT
SECDATA,18.612,18.612

TYPE,1
MAT,1
SECNUM,1
EN,1,2,5
EN,2,3,6

TYPE,2
MAT,2
SECNUM,2
EN,3,1,2
EN,4,2,3
EN,5,3,4
EN,6,5,7
EN,7,6,8

/SOLU

ANTYPE,STATIC
! Boundary conditions
D,7,ALL,0
D,8,ALL,0
D,1,UZ,0
D,4,UZ,0

! Loads
F,2,FX,1E3
F,3,FX,1E3

SOLVE