A question for the nerds

[Kansas]

I would like to be one, but fail miserably at it.

Had a customer send me an email wanting a price on 6x6's 14 ft long for a pole barn. I shot back a price on both the full measure and the lumberyard measure. Then I got to thinking. What size of white(bur) oak would have a comparable strength of a pressure treated pine one. I ran into this a few years ago when I built my house. Put exposed oak stringers to hold up the loft. They couldn't seem to find specs on oak, so they went with what it would be if Douglas Fir was used. As such, I have 1 1/2 by 12 inch oak on about 14 inch centers. You could put a tank up there and I don't think it would fall through. These were professional builders who simply couldn't find the answers, and they tried. Is there some sort of conversion rate between pine, fir, oak, any other species, for strength in building? My guess is a 4x4 oak would be as strong as a pine 6x6.

[POSTON WIDEHEAD]

Is the customer ordering 6x6's for POLES, or STRINGERS?

[LeeB]

Won't help you with postsbut will give you stength comparisons for joists and rafters in many diferent types of wood.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

Some more stuff that might be interesting.

http://www.awc.org/calculators/index.html

[Kansas]

Its for posts for a pole barn.

[drobertson]

Kansas, I checked the chart, and think that the pine with the numbers you gave is stronger.  I have ran into this a few times, almost the same senario, I stay away from design. But I was thinking the same as you before I looked.

[Larry]

Understand Wood by R. Bruce Hoadley is the first source I check for those type of questions.  A little chart gives strength properties of most common woods.  A quick look this morning shows post oak and white oak but no bur oak properties. 

That book is really a great source to answer all kind of nerdy questions.

Check your loft as it may be far too weak for the Dallas cheer leading squad to do a cheer. :D

Larry the nerd. :-[

[LeeB]

Description
This section is from the book "Building Construction And Superintendence", by F. E. Kidder. Also available from Amazon: Building Construction And Superintendence.

Strength Of Wooden Posts
For wooden posts in buildings used for ordinary purposes, when the length in inches does not exceed twelve times the least thickness, the safe strength of the post may be obtained by multiplying its sectional area in square inches by 1,000 for long leaf yellow (hard) pine, 900 for Oregon pine, 800 for spruce or white oak, and 700 for white pine. For machinery or full permanent loads (as a brick or stone wall) these values should be reduced one-fifth.

The safe load for posts whose length in inches exceeds twelve times their least dimension may be computed by means of the following table, allowing four-fifths for Oregon pine, three-fourths for oak and Norway pine, and five-eighths for spruce and white pine of good quality:



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prev: Appendix B. Tables Of The Strength Of Materials
Table of Contents
next: Table III. Safe Load In Pounds For Yellow Pink Posts (Round And Square). Crushing Strength Of Timber Perpendicular To The Grain


Read more: http://chestofbooks.com/architecture/Construction-Superintendence/Strength-Of-Wooden-Posts.html#ixzz2IF4wtwLL

[Kansas]

I don't want to give engineering advice, being I am not one. Had a few engineering failures in my life. My goal is to have some sort of chart or formula that I can give a customer so they can make the  decisions. The price for a 5x5 is way less than a 6x6. Being we cut everything anyway, a custom size does not hurt anything. My whole goal is to provide as good or better than what they can get at the big box store, and be competitive.

I need to work more with Lee's charts. Lot of good advice.   

Larry, if the Dallas Cowboy Cheerleaders fall through the loft, then they might want to go on a diet. But I will personally examine each one before they dance concerning weight restrictions.

[Radar67]

If you look in the Tool Box provided on the lower left of this page, there is a Column Calculator in the section named Don Ps Calcs. You will have to get some information on the wood you are using, but it will tell you what load capacities the wood will carry. There is also a beam Calc there.

[SwampDonkey]

The USDA Wood Hand Book, which is free, has all kinds of math and figures on this. Why buy a book? ;) I can bet there would be no more info in there, you might have to look a little bit and maybe just use a spread sheet and use the formulas to make your own tables. A lot depends on moisture and density almost as much as species. And yes the forum Toolbox has stuff.

[pri0ritize]

What kind of loading are you talking about on the posts? There is compression strength which is going to be extremely strong in any species of wood you use and then there is the load you support in a rafter or beam type of situation. White oak is anywhere near the strongest when it comes to this type of loading.