Hi Paul,
Wood that has been left in the round is considerably more robust (approx x 2) than wood converted into square or rectangular sections. The reason is simple and that is that none of the fibres have been cut thru and therefore failures due to slope of grain are greatly reduced. The grading process and assessment criteria used on converted wood requires a detailed inspection of all 4 faces with measurement and arithmetic cummulation of the various defects encountered. Since a pole does not have sides this methodology would prove somewhat difficult to apply.
You could search for Ben Law's book on building his cruck framed house in his woodland in South East England at
http://www.ben-law.co.uk/books.html using sweet chestnut poles. I do recall that Ben discusses some engineering aspects associated with this build though to the best of my knowledge he is not an engineer.
Roundwood is used from time to time in building and maybe the most famous endeavour in this respect was the various award winning buildings by John Makepeace who set up shop at Hooke Park, Beaminster, Dorset, England see
http://www.aaschool.ac.uk/AALIFE/HOOKEPARK/hooke.php for further details.
Please don't be put off your quest - a little research will yield dividends.
Regards
Ken Hume
