On Mon, 24 Aug 2009 20:46:20 +0100, Peter Crosland wrote:
Sounds like you need the services of qualified structural engineer to advise
you.

Quite possibly - although what would they do (purely out of curiosity)?
Would they cook up some 3D model of the structure, take samples of
materials and weigh, and work it out from that? I'm intrigued by what the
exact process would be... (mainly because I'm surprised anyone can give an
exact answer without a truly enormous - and perhaps impractical - amount
of work, although I'm sure a reasonable estimate based on a few
calculations and a lot of experience could be attaioned)

cheers!

J.