Some interesting discussion on CEHX about weights used to stabilise spires. (If you don't know CEHX you may be missing a treat. It is a mail list. The full title is Civil Engineering Heritage Exchange. People from all over the workd ask and answer questions about issues. I reckon the average is only about 2 or 3 emails a day, maybe less. Follow the link to sign up. If it gets too much you can always sign out again).

My friend Rainer Barthel and his company are working on Freiburg Munster. They had a wind tunnel test done by Wacker Ingenieure where there is a picture of the model. It was made from a 3D autocad model produced by phtogrammetry. The actual test piece was 3D printed direct from AutoCad.

Anyway, the interesting thing is that the wind force on this perforated spire is greater than on an equivalent solid one. Rainer's diagrams below show how the forces are made up from forces on each side and how the change of direction of the side panel forces is important.

These are the forces on a solid spire. The total is shown in the centre.

and these on a perforated one shown to the same scale.