Never heard of that limit - I've always taken Ft = 0.6 Fy and the shear allowable stress, Fv = 0.4 Fy. For a write-up on allowable stresses of steel in tension, check out AISC 9th Ed., Part 5 Chapter D.
1000 to 1200 kgf/cm2 is a usual tensile strength assumed sometimes when one does not wants elongation in rebar affecting negatively the contraption. Also for piles the service level allowable axial stresses go under than 0.4Fy. Of course for a site where you don't know why it is being applied for, must be conservative assumption.
