Quarter sawn stair stringers?

[forrestM]

Hey, would quartersawn white oak make good stair stringers? Is it less or more structurally sound being quartersawn? I don't need to use it, but I have some nice material on hand and I would if it is structurally sound. 

Thanks!

[Don P]

If its for show they will show more as treads than stringers. structurally fine, we do not distinguish a difference, or rather it is down in the weeds compared to the other strength variables. It will change more in thickness than width, which for this use, is a good compromise.

[beenthere]

And may depend on having straight grain along the tension side. 

[Larry]

Nothing scares me more than building stairs (well maybe decks).  I have this recurring dream of two 350 pound guys carrying a refrigerator down the basement stairs that I made.  We don't have any building code enforcement where I'm at but I make Dang sure my stairs exceed code requirements.

[scsmith42]

If its for show they will show more as treads than stringers. structurally fine, we do not distinguish a difference, or rather it is down in the weeds compared to the other strength variables. It will change more in thickness than width, which for this use, is a good compromise.

Don, for stringers wouldn't flat sawn be stronger?  I'd worry about QS stringers separating along the growth rings from the load.

[Stephen1]

I was thinking like you Scott so I will follow along. 

[Don P]

It's probably time for me to reread that section with you.  I'll look but I'm home from the docs, my sammich is gone, and the sun is shining  ;D.

[Don P]

This is the index to the Wood Handbook;
FPL 2021 Wood Handbook Easily Accessed Lab Notes (usda.gov)

Chapter 5 is here;
Mechanical Properties of Wood (usda.gov)

From table 5-1 it looks like radial, quartersawn WO is about twice as stiff as tangential. What Scott is talking about would be horizontal shear That is the GLR and GLT columns in the same table, it looks like tangential is about 50% stronger in horizontal shear compared to radial. And of course what is the one species with no printout on GLT, WO.

As always, you can't have your cake and eat it too, I can say stiff controls in beams more often than shear, shear tends to control in shorter, deeper, very heavily loaded beams.  In WO the rings and rays are at 90 to each other and either is a wonderful cleavage plane. I guess were back to rift  :D.

Notice they keep giving the average of radial and tengential in the wood handbook tables so it is hard to reall get a definitive if you are looking for ultimate performance.

A little background on the many strength tables you are scrolling by there. Those are average ultimate strengths of small clear samples. Not bad data if you are looking at performance or comparisons between species. When building the tables of "allowable strength" I use were originally derived from this optimistic data but are more concerned with about half the strength of the weakest 5% of the tests in order to account for defects, variability, time, etc. What I'm saying is if you are building surfboards, use these tables. If you are building houses or something where life safety rules, use the building tables.

I started reading the wood handbook when I was 16. I started understanding it when I was in my 20's. I found this in chapter 4 which is where my fingers go for this in my most used copy. To show y'all i looked up the modern digital version above and its now in chapter 5, the book is always getting bigger  

[scsmith42]

Don, I always feel smarter after reading something that you wrote!   :D

Wow - the 12% live oak numbers from the table are impressive!

Thanks much for the info.

[forrestM]

@Don P so, if you put that in layman's terms, quarter sawn stringers are bad, good, or just different in different ways? 

[Don P]

I'd say different in different ways. Back in the real world if you size things by the published allowable design strengths they are pretty well padded. I think grade and the individual stick probably means more than orientation, no major defects, watch the angle of the grain. And pics  .

If it is ultimate performance, the lightest hockey stick or bat per weight or size, then this comes into play. At least for full impact on a cantilever, hit the ball with the quartersawn face.

Scott, it was the capitalized abbreviations  :D.


Edit, just as an aside. I ran the numbers on a set of notched stair stringers one time and got into a discussion with a bunch of building pros and inspectors online. It doesn't work and they break the notching rules. Don't look behind the curtain  :D