Boxed Heart or Quarter Sawn

[Rodger]

Greetings,

I have a few questions for the more experienced in the craft.  Is it necessary for posts and structural members to be boxed heart?  I have some pretty large oaks that would yield 5 or 6 beams quarter sawn.

Thanks in advance  

[rusticretreater]

You can certainly cut beams from any part of the log.  You just do not want pith wood on a face of a beam.  You go to a box store and you will see beams cut from all sections of logs.  

Warping might be a problem depending on species and conditions.  It is just more stable if the pith is center of a beam as that is simply how the tree grew.

[Don P]

This is a link to "Green Oak in Construction", its big it'll take a minute or few.
Go to pg ~24 and then starting about pg 64;
forestry.gov.scot/images/corporate/pdf/green-oak-in-construction-2007.pdf

[scsmith42]

Don, correct me if I'm wrong but won't a beam that is quartersawn on the long face be more likely to shear under load in-between the growth rings compared with a flatsawn beam with similar loading?

Similar to ring shake in a standing tree?

[Don P]

I've pondered and started to think the same thing, and then I started thinking about the plane I see checking on, and rays are the root cause of that cleavage plane. So is flatsawn worst? I went looking in the Wood Handbook and I just found it again in my '74 copy at 4-29. Crickets.

[scsmith42]

So modulus of elasticity is greatest for the quartersawn beam depicted in their drawing? I interpret that as the quartersawn beam will be stiffer, but it does not address failure.

I wonder what the differences are between QS and FS in terms of yield strength versus tensile strength? Is tensile strength the same regardless of grain orientation? For some reason I'm thinking that FS has a greater tensile strength than QS, but I can't quantify that.

[Dave Shepard]

I'll be splitting large red oaks into multiple 4x6 tomorrow. I think the designer wants the loft joists to look like they were made from linguine. He should have used a thicker pencil and just spec'd pine. 

There are going to move. Sawing oversize and trimming after can help, but not always.

[rusticretreater]

I wonder what the differences are between QS and FS in terms of yield strength versus tensile strength? Is tensile strength the same regardless of grain orientation? For some reason I'm thinking that FS has a greater tensile strength than QS, but I can't quantify that.

Modulus of elasticity is the rate of a material's tensile stress to its tensile strain(deformation). Stiffer materials have higher modulus.

The text above stated that "Similar observations have been made in tension."  In all areas, the 90 degree or perpendicular stress to wood grain is the best you can get.

[Ljohnsaw]

When you say quarter sawn, is that on the narrow face or wider face?

A beam will typically be placed so that the maximum depth is vertical, but the "quarter" grain could be running either way and still be called quarter sawn, right?

[Sod saw]

.


When I think of quarter sawn versus a "different"  direction, I visualize a floor board and how it is oriented when installed on a floor with the grain pretty much up and down.  With oak, the ray fleck would be most visible, as Yellowhammer strives to produce in some of his videos.

In the example, above, that Don had shown from his book, the drawing on the left (90 degrees) would be quarter sawn.

My question:  Is this assumption correct?  Always?   Even for larger beams with the grain horizontal when installed as in that left drawing?


.

[Don P]

The way I read it, QS showing on the wide face of a beam or stringer.

My mind has always jumped to Fv, horizontal shear in bending when I contemplate a beam with that 90 degree grain orientation.

Here's a pic I had, this is what my mind envisions happening when 90 degree grain is loaded in bending, horizontal shear;


Notice the greatest strain is at the ends, watch concentrating stress there to avoid propagating a check. BUT! the beam calcs do the shear check last because that is not normally the control. Shorter, heavily loaded beams fail in shear. Deflection/bending gets longer beams before shear is "normally" an issue. hmm, what is normal 

[scsmith42]

I wonder what the differences are between QS and FS in terms of yield strength versus tensile strength? Is tensile strength the same regardless of grain orientation? For some reason I'm thinking that FS has a greater tensile strength than QS, but I can't quantify that.

Modulus of elasticity is the rate of a material's tensile stress to its tensile strain(deformation). Stiffer materials have higher modulus.

The text above stated that "Similar observations have been made in tension."  In all areas, the 90 degree or perpendicular stress to wood grain is the best you can get.

Thx for the explanation, In terms of stiffness, I get what you're saying. But what about in terms of failure?

Where Im headed is wondering if a quartersawn beam will shear internally along the growth rings under the same load that a flatsawn beam would merey bend under?

An example of this would be a glass rod. It has a high tensile strength so it will resist bending better than other materials, but its yield strength is almost the same as tensile so it will fail when slightly bent. Versus a steel rod may simply bend but not break under a similar load. 

Wood is different because its strength is correlated with cellular orientation.

[rusticretreater]

Using the above pictures for grain orientation, how do you think beams would check, split and break for each of the examples?  It seems to me the rightmost picture, 0 degrees would split vertically while the leftmost 90 degree would split horizontally.  Who knows what happens with the center one.  

The horizontal split would still retain a good measure of stiffness being pressed together.  The vertical split would tend to spread apart and lose much more of its ability to resist forces.  Given the same pressure applied, I think the 90 degree would be less prone to shear.  Just guessing though.

[Don P]

It seems to me the rightmost picture, 0 degrees would split vertically

An Fb failure, a failure by fiber stress in bending. The extreme fibers, the bottommost fibers tear or split off depending on slope of grain. The math of the first check in the beam calcs in the toolbox

vs 

horizontal shear, the 3rd check in the beam calcs;

while the leftmost 90 degree would split horizontally.

[Brad_bb]

My recommendation for oak is the cut posts and beams boxed heart with the center of pith centered in both directions to even out the stress while drying as much as possible. 

When it comes to braces (4x6  or 4x8)  you can flat saw or quarter saw them leaving the pith out.  

When it comes to 4" thick rafters, you can quarter or flat saw them free of heart, or boxed heart.

TIP: Design your rafters to be broken up into shorter lengths.  4" Thick oak rafters that are long will want to bow, crook, or twist.  Shorter will minimize those effects.  I learned that lesson the hard way with 20ft rafters on my shop and 30' gable end fly rafters on each end.  I had many culls that bowed like bananas.  Split heart will not help either.   If I can keep the lenths to not longer than 12 feet, then you'll have less loss with oak.  Quarter sawing is good, but more material loss and takes more time/cost so it isn't always practical.  I have seen local barns with Q-sawn oak rafters.

With oak, if left to air dry too long, you will get movement in some.  The only way I avoid that is either get it cut and raised quickly, or cut the timber oversized and after they air dry for  1+ years to stabilize, I use my mill mounted beam planer to true them up square and to final size.

[Magicman]

This is a small Oak log but even so, 7 of the 4X4's should be OK.
I would have preferred that none had sapwood, but I was trying to squeeze all of the "juice" out of the log.  I needed 5, so I should be OK.