Periodic Boundary Conditions for uniaxial compression

Dear All,

I am trying to simulate mechanical behaviour of a concrete unit cell for uniaxial compression laoding. I have apllied periodic bounadary conditions on both lateral edges using linear equation option available in ABAQUS where as on top and bottom edges load is apllied. Deformed structure shows there is no lateral deformation and unit cell behaves as if it is confined laterally on both sides. I am confused about my boundary conditions whether they are correct or not.

 Equation used to aplly periodic bounadary condition are

** Constraint: Constraint-18
*Equation
2
R17, 1, 1.
L17, 1, -1.

where R17 and L17 are nodes on the right and left of the unit cell.

The above eqn I could use from your earlier suggestion but

Can any body suggest what exactly I should use  for my unit cell. Unit cell is a plane square with a circular inclusion at the centre.

 Regards

 Gouse