shr,
I did not say that settlement is a sustained stress. Clearly a sustained stress that truly exceeds yield will cause rapid failure.
For sure, do it your way, but you would probably need more pipe, more restraints and springs .... It is common practice to do as I've explained above. The point is, settlement is a one-off load which is similar to an expansion (secondary) stress, which is self limiting, and can thus be allowed to exceed local yield stress.
Also note that in my experience, expected settlement figures quoted in basis of design documents are often grossly exaggerated.