White pine beam span table anyone?

[hunz]

I have been trying to come up with a EWP beam span table of some sort, with little luck. I am currently building a wrap around porch on a timber frame house. The architect has spec'ed most the 6"x6" EWP porch posts at 6'-7' apart. Well I Installed them as drawn, and man is that way too busy for me. I can't even see out of the windows of my house without seeing the center of a post....not gonna work.

My game plan is this, remove every other post to open things up, making my furthest span 15'-5" on the porch. I was told a 4"x8" ewp header can only span 10' max in-between posts. I'm wondering if 4"x10's would be ample or if I need to saw up some 4x12's. Any insight would be much appreciated.

Thanks

[jimdad07]

The forum toolbox has the engineering calculators for your most common species, including white pine.  Very easy to use.  Good luck.

[Don P]

You are probably not going to get there in EWP. When you double the span, not only has the span doubled, the load has as well, the bending moment has squared. For spans like that I'd probably go to LVL's and wrap them. Look down, are the footings up to double the load?

[jwilly3879]

How wide is the porch?

[ChugiakTinkerer]

Using Don_P's calculator here: https://forestryforum.com/members/donp/beamclcNDS2.htm

The engineering properties for graded lumber species are codified by the American Wood Council.  Current values are available at: http://www.awc.org/pdf/codes-standards/publications/nds/AWC-NDS2015-Supplement-ViewOnly-1411.pdf

Table 4A gives the reference design values for Eastern White Pine.  The values we need to know are for Fiber stress in bending (F_b), modulus of elasticity (E) and allowable horizontal shear (F_v).  For EWP #2 those values are 575 psi, 1.1 million psi, and 135 psi.  These are base numbers that we may need to modify depending on the manner of beam chosen.

Table 4A in the NDS Supplement has adjustment factors that need to be considered.  For a 4x8 beam (assuming rough cut so using full 4" x 8") the F_b size factor is 1.3.  This results in a Fb of 747.5.  Now go to the beam calculator and plug in the relevant numbers.  Input these values and keep them constant: Span 186", width 4", depth 8", fiberstress in bending 747.5 psi, modulus of elasticity 1,1 million psi, and allowable shear 135 psi.  Now input a load of 1000 lbs in the top field and click Show Result.  You will see the beam passes.  Add 100 lbs to the load and click Show Result.  Keep doing this until the beam fails.  You will soon arrive at the max load for the beam of 1375 lbs.

For a 4x10 beam of #2 EWP apply the size factor of 1.2 to arrive at a Fb of 690 psi.  Update that value in the calculator, and set the beam depth to 10".  Going through the same process you will find that the maximum load for the 4x10 is 1970 lbs.

For a 4x12 beam the shape factor is 1.1, resulting in a Fb of 632.5 psi.  Using that and a depth of 12" the maximum load for the beam is 2610 lbs.

Using a built-up beam of three or more stringers nailed together allows a 15% increase in the bending fiberstress.  A 6x10 beam consisting of three 2x10 nailed together has Fb of 727.35 psi.  Using that value and a width of 6" and a depth of 10", the max load is 3140 lbs.

For reference, a 4x8 beam of EWP #2 spanning 90" like in the original design has a max load of 2840 lbs.

The load that the beam must carry is determined by the depth of your porch and the design load for your area.  The house is holding up half of the porch roof, and the beam the other half.  Multiply half the porch depth by the beam span to get the area.  Multiply that by the design load, which is the sum of the dead load and live or snow load.  Assuming 10 psf and 20 psf respectively, that is 30 lbs per square foot.  For a porch 8' deep and a beam span of 16', that equates to a design load for the beam of 1920 lbs.  Your architect designed for the specific values for your area and those should be noted within the design documents.  Based on my assumptions and further assuming all my calculations are correct , it looks like a 4x10 will be adequate for that span.  If your porch is bigger or you have more snow in the area then a bigger beam or better quality wood will be required.  If your build has a permit inspector, then the first thing to do is check with that office and verify that your plan change is allowable.

[hunz]

Chugiak, great info, my question is now answered in crystal clear fashion. Thank you for taking your time to explain all of that step by step. I had found the Fb and modulus of elasticity for EWP on the AWC website, I was just unsure how to use them to calculate what I needed to know. Now I do!

Awesome, and many thanks!

[ChugiakTinkerer]

My pleasure.  Just remember that with any advice you get on the internet, you should verify with a trusted source.

[Don P]

The area bearing on the beam is half the porch width, plus the overhang.

EWP is a stretch here IMO. If you rerun that scenario with a 1' overhang you're overloaded. If you have access to enough forest grown largish trees this may work. The growth habit of EWP makes if difficult to get the beams that math is describing, certainly not impossible, but it will take a critical eye when sawing and grading.
... Is there a reason not to go to something that is stronger and has better knot structure... hemlock, poplar, oak, maple come to mind.

[hunz]

Knowing that I live in western North Carolina, I am leaning toward max psf loads of 20. We maybe see 30" of snow per year, occasionally 50" max. The company that installed the shell for my house has 4x10 ewp rafters on 4' centers spanning 20', and those plans are stamped by a structural engineer.  Given the psf number of 20, even with a 1' overhang, I am under what a 4x10 spanning 15'-6" #2 can withstand. Most of the porch spans are 12.5-14.5 feet, the furthest is 15.5'.

I live on 500 acres, and can have my pick of poplar, oak, maple etc as you mentioned, but I'm into continuity with my pine timber frame home. It's the home I plan to die in, and I want it to look thought out from the get go, not shifty alterations as I build. Thanks for mentioning the overhang since I didn't account for that in my figuring.

[hunz]

Here are several pictures of the timber off my farm that have been sawed for the house

  

 

[Remle]

Okay, they say the only stupid question is the one you don't ask. So here's my question, would it be possible to make the width of the beam 6" wide ? You said in your first post that the post were 6X6, a 4" beam sitting atop a 6" post seems odd to me. The extra width may make the beam pass in all areas of the calculations.

[hunz]

Haha, that is a true statement. I unfortunately already made seat cuts for 4x8s, then had to make them deeper after I made the move to saw up 4x10s. I already have the front side of the house up in 4x10's , so I'm hoping it will be fine. I'm waiting on a call from the head building inspector on required roof design load. We'll see.