A guyed chimney stack is very similar to a yacht's mast - so before starting the final design, I suggest a few days out on the bay. Observe the rigging. On the windward side, it is all tight and straight. On the leeward side, the rigging hangs loose, and does nothing.
It is the same with a guyed mast or chimney. When the wind reaches the ultimate level, the guys to windward will all be tight, and there will be virtaully no load on the other two or three sides. So design each guy to react its share of the wind load. There is no need to worry about non-linearities - by the time the guy is ready to break, there will be virtaully no sag.
Design the mast/chimney for the bending loads between guy points, assuming a continuous beam fixed at each guy. Then check the deflection pattern of the mast, to make sure it is achievable, with an acceptable amount of plastic redistribution. If not, then it might be necessary to move a guy, or make some parts over-strong.
Vortex shedding from the guys or mast can be a problem. It helps to pre-tension the guys to raise their natural frequency, but take care not to buckle the mast as a column. (Note that when the loads reach the ultimate limit state, the down-wind guys have relaxed, and the preload in that direction plays no part, but the preload on the guys at right angles is still there.)
If the mast vibrates, the sailor's solution is to wrap a rope around it in a spiral. A 16mm rope will dampen vibrations in a 250mm diameter mast. (The light towers on the Stand at Townsville survived the last cyclone!) A similar solution can be used for chimneys. The spiraling vortex breaker does not need to be very large, and doesn't contribute greatly to the overall drag.
Cheers,
RHK
Russell Keays