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Structural stability/properties of round vs square post and beam

 
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Hey all, so I'm about a quarter of the way through Rob Roy's Timber Framing for the Rest of Us. The book is primarily focused on using recti linear timbers and I was just reading in it about how round beams have a significantly lower sectional modulus compared to a squared off beam. Their specific example was an 8 in diameter beam having around 60% of the sectional modulus of an 8x8. Is this simply because the 8x8 would have had to be milled from an 11in diameter tree, assuming perfectly efficient milling? In my mind the vertical posts should pretty much always be better round as opposed  to square since you have no grain run off and the trees are designed to take very high compression in the direction of the grain. For beams my understanding is that if you have to shave them down for tenon's or Lincoln log style  notches then that becomes the weakest part of the beam.

I am currently trying to research and plan for wofati/oehler style structure hopefully to begin construction next summer. The goal is to ring bark some cedars on my current property and fell them this fall to allow them to start curing and drying to use next year. We are currently planning on buying a portion of a good friends property that is on a decent incline so drainage shouldn't be a problem and is uphill of a semi major river well above any possible  floods. The current goal is a single incline shed style roof around 32 by 16  with 8 foot spans to move into and expand from there.
 
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From log cabin building

This technique leaves the sapwood on the log which is not as strong as, and is more prone to damage, than the inner heartwood.

 
David Pritchett
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John C Daley wrote:From log cabin building

This technique leaves the sapwood on the log which is not as strong as, and is more prone to damage, than the inner heartwood.



Thank you for that site! I hadn't run into that one yet and it looks like it will have tons of good info. All of my knowledge on this stuff is summed up in Mike Oehler underground house book, Rob Roy's Timber Framing and cordwood books and one about adobe/earth building.
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