shearwall modeling

huangyhg

shearwall modeling
been modeling a group of walls, basically a square tower, in both staad and ram and am not satisfied with the reactions from a lateral wind load applied at the centroid of the top of the wall group.  the reactions in the direction of the applied load are correct it’s the perpendicular direction; they are equal but in opposite directions at each side of the square.  they cancel each other out but why are there any at all?  also why would they differ from staad to ram?
any help is appreciated.
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the reason those equal but opposite loads are there is because the individual   
without knowing the geometry this is difficult to answer, but are the walls with the equal & opposite reactions resolving a torsion induced from eccentricity between the point of load application and the centre of stiffness?