quercus

If it fails between the two rings, that would mean that the dynamics of the stem are still in place after installing the frame. The general idea for this is to take dynamics away for the entire section wich is braced. If it can't move, then it's not likely to break. The only way I see this happening if the trunk would collapse on a horizontal axis.

I don't really know how the situation is on 9 m above ground, but if it is severely decayed there, I see the tree breaking apart just above the upper ring. If it were to fail at that point,possible damage and risk would increase severely.If uprooting would occur, the tree would fall down more gently and more slowly then when a large section including the massive crown where to free fall to the ground. Don't know if my sentences are correct on this.

I'd create a steel bracing for the tree, all the way up to where it divides into the upper crown section. This would require a setup of a lot more square feet area then the one they designed now.Let's not forget that this ridgid design is either a case of making it, or breaking it.

The architects state, that it doesn't form a problem if the steel structure would deform a bit during the years to come, and that's something that I find hard to believe. I see only triangular shapes, and for a triangular shape to deform, one corner or side must break. If this would occur, the structure would become worthless.