Lumber Strength?

[Russ Filtz]

Was going to use some 2x4's for shelving support, but had to lay them on their sides due to height restrictions. Someone said I should have used two 2x2's as they would be stronger.

Initially I though this was wrong since they are the same shape and material, but then got thinking about grain direction. Is a 2x4 cut normally with the grain stronger when "on edge" or does grain in wood not affect strength much? I was thinking if the grain in a square wood piece was pretty much linear, or in a plane, then putting the grain on edge would make the piece stronger. Thus two 2x2's oriented correctly could be stronger than a 2x4 on it's side?

[Gary Whitt]

Most 2x4's are flat sawn. When they are stood on edge, you'll be looking at quartersawn grain.
With a load, quartersawn should be stronger; flatsawn might tend to snap at the growth rings.
When using lumber for supports, no matter what dimension lumber, try to have the grain lines more right to left (quartersawn like these parenthesis marks) rather than up and down (flatsawn).
Hope this didn't confuse you.

[Jamie Buxton]

Russ ---

There is more meat in the 2x4. The 2x4 is 1.5"x3.5", while the doubled 2x2s are only 1.5"x3.0".

As to the grain orientation you describe, my bible in these issues is Bruce Hoadley's Understanding Wood. He makes no mention of this affecting stiffness.

...you are asking about stiffness, right, not breaking strength? They are two different things...

[Russ Filtz]

That's kind of what I thought. Then if you wanted a "flat" 2x4 for a support, then it would be better to rip it in half and flip the "new" 2x2's on "edge"? Should be stronger right, even given the minor wood loss due to the cut>

[Russ Filtz]

Jamie, I guess I'm talking both, but from an engineering perspective I would expect both factors, stiffness and breaking, to be better with proper grain orientation (mainly breaking strength I guess). Maybe not markedly different, but it should be there. The ex-carpenters in the office say it's something they intuitively learn while on the job.

[Joseph N. Myers]

Russ,

If strength is an issue and your are limited by space, you may want to use something other than softwood for your supports. You could use hardwood, "lipping" with hardwood, i.e., glue/nail a piece of hardwood along the edge of the 2x4 or whatever, use metal bracing, etc.

Of course, shorting the span, bracing between the supports (i.e., shape of an "h"), attaching a piece of plywood to the braces, attaching piece of plywood to both the top and bottom of the supports, i.e., "honeycomb" structure which is quite strong.

Regards, Joe

[Russ Filtz]

The structure I built turned out plenty strong with just the 2x4' sideways. Only a 50" span. Just a theoretical discussion now.

[Jamie Buxton]

There's nothing like real measurements....

I just went out to the shop and found a piece of red oak 2x2 which happened to be quartersawn. That is, two of the faces are radial in the tree, and the other two faces are tangential to the growth rings. I set it on supports which are four feet apart, loaded it in the middle with a 20 pound lead window weight, and measured the deflection in the middle. I did this in the four possible orientations. The two orientations where the loading was radial in the tree had deflections of .050" and .054". The two orientations where the loading was tangential to the growth rings had deflections of .052" and .054".

That is, there is no real difference in stiffness from the growth ring orientation.

[Joseph N. Myers]

Now that you mention it ...........

I would expect oak to be pretty much the same no matter what angle because of the tight grain and orientation. Pine on the other hand, has a very loose grain (notice how the growth rings will seperate more easy from pine than oak).

However, thinking about quarter-sawn, its main claim to fame is its "stability" with respect to shrinkage movement when drying and strength at the surface, e.g., use as a cutting board.

Regards, Joe