relative strengths of different species

[handhewn]

I was reading some threads herein on various wood species strengths and I remembered something I did way back that still pops up in my mind. I put two pieces (one at a time) of yellow pine and doug. fir in a compression testing machine in the materials testing lab at Chico State univ. They were each clear and sized 2"x2"x6", stood on end in the testing machine. The Yellow pine failed at just over 4000 lbs. The Doug fir maxed out the machine at 20,000 lbs. without failing although it was starting to slip some grain. Just some info for you to ponder on relative strengths of various species.

[Don P]

Some thoughts that come to mind.
The sample size is quite small, 1!
There is large variability in individual samples, even though this is a very large spread.

Off to the bookshelf, hang on...
From the Wood Handbook, I think these are similar sized, straight grained, clear specimens. Table 4-2 uses a much larger sample group, these are average ultimate compression parallel to grain numbers
DougFir ranges from 6220psi for Interior Southern to 7440psi for Interior West. At 4 square inches your 20,000 psi reading would be 5000 psi, indeed too small of a machine for an accurate test of samples of this dimension. Which makes me wonder about the apparatus in general, this was the wrong tool for the job, were the holder and ram capable of doing their job correctly.

SYP average ranges from 7130 for lob to 8,470 psi for Longleaf. At 4,000 lbs on a 4 square inch sample you got 1,000psi, an unusually low sample, I wonder what the issue was with that sample.

Table 4-5 states that there was an average of 18% variation in their samples of that property. Was the sample unusually light or did it have some other abnormality?

Closing that book and off to the shelf again...
When I am looking to use a piece of wood structurally I don't use those average ultimate strength numbers, that would be quite dangerous. If you were testing in the materials lab I'm sure you saw some sampling plots. The plots of the breaks looks like a shotgun blast of points with an average line drawn through it. If I used the average strength to build with, and built with many pieces of wood, most of my buildings would collapse.

I use the allowable stresses published in the NDS Supplement, The builders and engineers book of design values and the ones i talk about on the forum. After grade sorting they have applied a 95% exclusion limit (95% of wood in that grade will be stronger than the initial limiting strength assumption), That is then multiplied by a factor of safety, I'd have to dig but around 2x, and a little more magic outlined in the ASTM references (the "grade quality index") and they come up with the allowable design strength value that we use for building with. In other words a good bit of the wood we use is substantially stronger than the "allowable" assumption to keep things safe. Where I'm heading is I'm about to open that book and see if that SYP stick at 1000 psi failure was still safe or not. (I did go to Lowes and dug out a 2x4 that broke below allowable in a bending machine, lesson being still look at the wood you are using, the grader might have been eating a donut.)

OK allowable compression parallel to grain SYP, I'm going to look at Select Structural, the clearest grade but certainly allows some defects. 2100psi, Wow! That 1,000psi clear stick was a problem! Now compare that allowable 2100psi to the average compression strength of clear loblolly 7130psi, generally there should be quite a safety margin. SYP doesn't go that low till you get to #3 and stud at 975psi.

Allowable on SS DougFir ranges from 1,600psi to 1900psi depending on species combination and growing region.

Where I'm going is, that is anecdotal based on a sampling of one. I'm seeing issues with the testing method. I don't think I would use that to base an assumption of the relative strengths of those two species on.

Interestingly I got an email today from the grading authority. A company in the southern hemisphere is trying to get acceptance to sell their SYP decking here. They sent some samples to a university here to be tested, from one sawmill and 80% of the samples they sent were clear. The testing protocol says you test the worst. I'm guessing they will be consolidating stock from multiple mills across the region and I doubt the material will be that fine. And yet, they got approval. Ultimately we are the end user, keep your eyes on the ball.

[Southside]

So in a nutshell.

OP - SYP is wimpy compared to DF

DonP - Hold my books, they are numerous and heavy....

Actually a really good post to read and I am just responding to both in good humor.

:D

[handhewn]

Funny thing is, that was about half a century ago and I don't remember much but that there were various woods used besides the fir and yp. I don't remember those pressure outcomes. I can say they were all clear straight grain heartwood.

[Ianab]

DonP - Hold my books, they are numerous and heavy....

My take away from this.

DonP should build his book case from Douglas Fir as it can support more books :D

A company in the southern hemisphere is trying to get acceptance to sell their SYP decking here

Radiata pine by any chance? That's the most common pine grown in NZ, Aussie and Chile. It should compare with Pinus taeda and other SYP species.  But because it's not officially in the "club" I'm guessing it can't be sold as such? Unless it's officially tested and stamped "meets SYP standard". 

Pruned radiata butt logs would probably yield ~80% clears, but decking isn't usually sawed from those, they are too valuable. A few tight knot boards from smaller top logs would make the grade though. 

[Don P]

Pinus Taeda, the lowly loblolly, from Uruguay.
At a certain point it isn't a problem that is simply species dependent, the spans are too great for the load, you need thicker shelves  :D.

[Ianab]

Pinus Taeda, the lowly loblolly, from Uruguay

Interesting. But no reason it wouldn't grow there. climate would suit. 

[HemlockKing]

Pinus Taeda, the lowly loblolly, from Uruguay

Interesting. But no reason it wouldn't grow there. climate would suit.

We even have lots of lobloly growing here in NS. Obviously it gets out competed quick if not managed but it will grow here, although not the greatest on a lot of sites, they seem to get spindly and not have much needles, in the 70s when the new highway got put down they also planted these along the offramps, they seem to do best there(in the open sun).

[Don P]

Between the two of us we've planted over a million of them. A common name for loblolly used to be old field pine, they do like full sun. My issue wasn't species related it was the approval based on faulty testing procedure.

I wasn't there but if I had to guess on the low failure in the op I'm betting on cross grain in an otherwise clear sample. The shear design value for SYP is 175 psi. Slope of grain is probably the most important strength limiting defect.

Let me put one on your bookshelf, this is the chapter from the Wood Handbook on how those allowable design values are created;
Wood Handbook--Chapter 6--Lumber Stress Grades and Design Properties (fs.fed.us)

The new book last week was a neat score. I happened across Ben Brungraber's "Timber Design for the Civil Professional Engineering Examination" for under $10 used online. Dated but what a gem, full of examples and explanations  .

[Dad2FourWI]

The species does make a difference...... we sell our slow growth, central WI Red Pines to Bell Timbers and they supply Utility Poles in many countries.... both Red Pine and SYP. They keep track of all the poles and when/how they break, when they are retired, etc.....

They prefer the slow growth Red Pine because it will prevail when the the SYP breaks in storms! Unfortunately, they do NOT pay us more for the Red Pine ..... but I am working on that!!!! !!!

[barbender]

I don't know about that...SYP is stronger than our red pine in pretty well every way. I've watched a harvester down in Georgia cutting SYP, if they left a 1/4" strap on the back of a felling cut, it would tear all the way to the top of the tree. That fiber is really strong.

[Don P]

Gotta run but take a look at this... on "heavy papers" I read the intro and skip to the conclusions to get a quick read. The body of this has some of those shotgun blast strength tables I mentioned before, looks like interesting reading;
Southern Pine Strength Verification (woodpoles.org)

[samandothers]

Don,

Looks like the numbers show SYP compression higher in compression to DF:

"OK allowable compression parallel to grain SYP, I'm going to look at Select Structural, the clearest grade but certainly allows some defects. 2100psi, Wow! That 1,000psi clear stick was a problem! Now compare that allowable 2100psi to the average compression strength of clear loblolly 7130psi, generally there should be quite a safety margin. SYP doesn't go that low till you get to #3 and stud at 975psi.

Allowable on SS DougFir ranges from 1,600psi to 1900psi depending on species combination and growing region."

Did I read this correct?

Also the book for prepping for the Prof. Engr. test is one @DWyatt can skip now!

[Dad2FourWI]

Yes, I have read the hardness comparisons of SYP as well..... but Bell Timbers has been tracking the utility poles of both SYP and Red Pine for years and in use in many different countries..... and the Red Pine are preferred.

Maybe it is exactly what the hardness is indicating. The hard SYP utility poles "snap" and break where the Red Pine just take the beating of winds, tornados, hurricanes, etc.

For our use here on the farm it is a mute point..... .... we have lots of mature Red Pine and not one stick of SYP.  :D   

It's similar to the old saying for firewood..... "What kind of wood do you burn? Whatever is in the woodshed!"

Cheers!

[Don P]

It's semantics, but when your talking about this stuff semantics does matter. Hardness is yet another mechanical property, measured by pressing a steel ball into the side grain of a stick. If I'm looking at flooring, hardness matters a great deal. What matters... or what they specify in poles is bending strength and stiffness, in both cases SYP shines there... but!, track record in use is what matters for that use. Utility poles are pretty well tracked and monitored, if red pine is working better for them in that application that is what matters. They are not drawing a conclusion from one sample so there is certainly something to it. Bear in mind we are just speculating as to the why. I would not go from their experience to thinking that red pine is stronger or better for a typical construction member. I did look this morning in the log home full round log strength tables and SYP was well above red in that use as well, and I've used both as lumber, SYP is considerably stronger and stiffer.

Sam, yes, SYP is stronger in compression parallel to grain than DF, but!, those are the two premium strength softwoods in the lumber market. If you need strength chances are the designer will use them pretty much interchangeably, the next step above those I'll see them call out a LVL and for "regular" work I'll typically see something like #2 SPF or better called out. So if I see a note specifically calling for SYP or DF, especially if it is a callout for SS or #1, I take notice, he's telling me something about span or load or both.

[Dad2FourWI]

Thanks Don P, good points!

We find our White Pine too brittle for construction as well... we occasionally bump into a post or two and the White Pine posts (from our farm) break very quickly.... in the CTL I could not even tell I hit the bloody post! HA! Where as the Red Pine fight back!!! 

No Red Pine floors here.... exactly what you said, they are soft... we stick with Red Oak which we have dying all over the farm thanks to Oak Wilt.

I wish we had some DF.... but I better be happy with what I do have. Great conversation!!

[samandothers]

Creosote poles would give more and be more forgiving to a hit it tree load.  The green CCA would take so much and just break. Also climbing a green pole was harder to set hooks in than creosote. Creosote was messy and caustic to the skin though. 

[Don P]

Boy do I remember creosote burns, creosote and hot sun were a bad combination if you didn't have on long sleeves and gloves.

We've talked about cross grain weakening and round timbers so something else came to mind. When we saw a tree it is to make it easier for us to use, the tree was not built for such abuse. When a tree is growing it surrounds branches with straps of fiber that surround the knot. When we saw we cut through those continuous unbroken straps creating cross grain runout off the stick and really weakening the timber we have created. If you need strength and can handle the round log it is considerably stronger than a post or beam sawn from the same log. I know numbers make some of your heads spin, but I'm gonna do it anyway  :D. 
A large #1 beam sawn from SYP has an allowable bending strength of 1350 psi. If I use a log beam of the same species and grade it has a bending strength of 1650 psi in loblolly and 1950psi in longleaf. There is more engineering going on to design in round vs rectangular timbers but an unmolested timber is stronger.