necessiscity of periodic boundary conditions for uniaxial loading

Hi,

I observed that with
periodic boundary conditions on unit concrete unit cell, when uniaxial load is applied structure
behaves as if it is constrained to move in lateral direction, when
shear or other traction laoding is applied it has displacement
compatible behavior i.e, parallel edges has periodic deformation
behavior. With these above behavior can I conclude that for uniaxial
loading I need not apply periodic BCs and simply applying roller is
sufficient on lateral edges or there is no need to apply and periodic
BCs for uniaxial loading.

With refernce to my
above comment whether to use Periodic BCs for uniaxial loading, I found
a supporting paper which says for uniaxial loading periodic BCs are not
required. Reference paper is -

V. Kouznetsova, W.A.M. Brekelmans, and F.P.T.
Baaijens, An approach to micro-macro modeling of heterogeneous materials, Computational. Mechanics, 27, 37-48, 2001 

However still I am confused whether to use Periodic BCs or not, can any body clarify about this.

Thank you

Regards

Gouse