Its really quite simple and probobly a question most would know on here. please excuse my newby question. In my Sobon book it mentions that its ok to use the heartwood on post on the shed but not anywhere else. Is there a simple explenation of this. I know that in heartwood the timber shrinks radialy but in edge wood it shrinks uniformly but is there a structural issue with this?
Mortice,
What page you on?
Sorry, I'm at work, I'll have to look tonight. I thought I remember reading that in the section where he tells about the materials required for the shed. Became conversation between a friend and I because we were both under the understanding it is never good to use heartwood in timber framing.
Hard to figure out what the warning might be referring to specifically...but in general, heartwood has the lower quality wood (pith, knots, juvenile wood, etc.), although in compression as in a post, might be ok, whereas in bending as in a beam or joist may cause strength reduction on the tension side.
It may be a general recommendation....and I'll be curious to know more when you find the actual statement made in the book..
I found it. page 80. Timber frame construction (all about timber frame building) Jack Sobon and Jack Schroeder.
"Wood for the shed"
"The large timbers such as posts and beams should be center-cut, while girts, braces, rafters, and floor joists need not be."
So heartwood is stronger?
Quote from: Mortice on March 06, 2008, 06:43:20 PM
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"The large timbers such as posts and beams should be center-cut, while girts, braces, rafters, and floor joists need not be."
So heartwood is stronger?
Likely has to do with the center-cut yielding straighter posts and beams because of balanced stresses around the pith center, while the other material doesn't need to be as "straight"...no reference to heartwood being 'stronger', as I read it. ::) ::)
Beenthere's got it. I don't see any mention about heartwood, just center cut...which in this case is referring to "boxed heart" timbers where the pith (center of the log) is in the center of the timber. A timber such as a rafter or joist could still be heartwood even if it isn't boxed heart :P