Hi Peter

thnx for replying....Actually that's exactly what I want

i want to prevent it from moving in  the Z diretion ...then i wanna prevent it from moving in Y direction In order to set he value of each load multiplier these cases 

-Buckling in Z direction

-Buckling in Y direction

-Pure tosion about X axis

but how can i make that in Ansys???

beam is defind as line body ...

the first end is  defined through Remote Displacement 

(Displacement X Y and Z are 0 , Rotation X is 0 ,Rotation Z and Y are free)

the second end is defined too through Remote displacement 

(Displacement X is Free ,Y and Z are 0 , Rotation X is 0 ,Rotation Z and Y are free)....

but unfortunately when i add the third 
Remote displacement to prevent the all line Body from moving in Z direction I get an error message
(An unknown error occurred during solution.  Check the Solver Output on the Solution Information object for possible causes.)

and a warning message 
One or more MPC contact regions or remote boundary conditions may have conflicts with other applied boundary conditions or other contact or symmetry regions. This may reduce solution accuracy. Tip: You may graphically display FE Connections from the Solution Information Object for non-cyclic analysis. Refer to Troubleshooting in the Help System for more details.)


and the eigenvalue Buckling could not be solved ....