Since axial deformation is obtained from the expression Delta = PL/AE, you could set A (Cross section area) for the desired members to a very large value which will then ensure that the axial deformation of those members is small.
If you are specifying the properties through the GUI, go to the General-Property page, choose Define followed by General from the right side of the screen, and fill in the proper values for IX, IY and IZ, and a large value for AX.
If you prefer typing them in the editor, the property type should be PRISMATIC, and values for AX, IX, IY and IZ should be provided as suggested above. You can refer to example problem 8 for a guideline.
SKLose, thanks a lot. I have checked it and it works.