I am working on mechanical apdl and I want to apply a spring constant in moment in x (ROTX). I am adding this code to my model:

ET,3,COMBIN14

KEYOPT,3,1,1

KEYOPT,3,2,4

KEYOPT,3,3,1

R,1,Kxx, , , , , ,

RMORE, ,

N,500,0,0,-0.01 ! Extra node below the node in contact with the ground (node 1)

real,1

E,1,223

...

And when defining the boundary conditions:

D,1,UX,0,,,,UY,UZ, ROTY, ROTZ ! Fixing all the DOFs except ROTX

D,500,UX,0,,,,UY,UZ,ROTX,ROTY,ROTZ ! All DOFs fixed

Is there something missing? Thank you.