A little help for a non-timberframer please

warren46 · September 29, 2013, 03:58:54 PM

I would appreciate a little help to determine what dimensions I need for a beam to span a wide opening. I am planning to build a sawmill shed in the coming months. One side of the shed should be open with a span of 20 feet. The roof will be a shed roof probably 15 feet across. Snow load will be like Charlotte, North Carolina. I have a hickory log that is 21 feet long and 16 inch diameter on the small end that is a potential to make the beam but can also get red or white oak.
What else do I need to know to size the beam and what size is necessary? Should I have a beam milled now so it can season a bit before I build next spring/summer or wait until I am ready to build?

Thanks,

Warren

Jim_Rogers · September 29, 2013, 04:35:50 PM

Ok, well I looked up NC on my chart of snow loads and it says 10lbs to 25 lbs but nothing more specific. If you can find your exact snow load it would help.

Using 20' span and 15' width of shed, the load would be half the width as half would be on the back wall. So 20' x 7.5' = 150 sqft. x 25 lbs for no reason other than that's the top load = 3750 lbs. I used DonP's online calculator here in the red toolbox and entered in the values know. And selected red oak #2 B&S for beams and stringers, and suggested it try an 8x12 and it passed.
The calculator doesn't have a value for hickory that I can find.
Without knowing the hickory value I can't comment on whether or not that could/would pass.
If it was me and I had a choice, I'd choose oak and make it a 8x14 just to be sure.

Hope that helps.

Jim Rogers

warren46 · September 29, 2013, 06:13:16 PM

Jim,

Thanks for the suggestion. I will try for an 8X12 oak.

Warren

warren46 · September 29, 2013, 07:21:11 PM

Jim,

I checked on the snow load for Charlotte and came up with 10 PSF. It makes sense that we are at the low end of the range for NC since we are not in the mountains.

Can you tell me about the red toolbox? I'd like to take a look at how it works.

Warren

Jim_Rogers · September 30, 2013, 07:12:33 AM

The red toolbox is on the left side of the webpage. Click on it and it will take you to the toolbox list, I usually right click on it and select open in another tab or window, so you can have two things open at one time, if needed.

Scroll down and select "DonP" calculators. DonP is a member who is inactive at this time. Hopefully some day he may come back. But, anyway on his list of calculators I selected "Beam and column calculators". Then I selected the second one down for uniformly loaded beam with a drop down species list of wood types.

Next I had to add the live load on the beam. To figure the maximum live load I used 25 lbs per sqft and I figured the area. The area is 20' wide by 15'. But half that load goes to the rear wall so I used 20' x 7.5' and got 150 sqft. Then I times 150 by 25 and got 3750. I entered 3750 in the live load box. Then I entered 1500 in the dead load box I figured 10 lbs per sqft for the roof materials. Now if you're using some metal roofing you could ask the supplier what the weight per sqft is and adjust the value. But 10 lbs is the standard that is used. So that brings the total load up to 5250.
Next I entered the span of the beam in inches 20' x 12 = 240. Then I selected a beam to test. I entered an 8" wide beam 12" deep.
Next comes the select species and grade. There wasn't any value entered for Hickory. So, I selected red oak grade #2 B&S. B&S means beams and stringers. P&T means posts and timbers. The NDS figures if the timber depth is larger then 2" of the width that you are automatically going to use this timber as a beam. Beam means a horizontal member of your frame.
Then I selected "show result" The calculator enters the values for red oak grade #2 and then processes the test. The beam passed on all three tests.
If you adjust your loads you can most likely get away with a smaller beam, but don't go under 3" deeper then the width or you'll have to change the pull down list to P&T and these values are lower then B&S.

I would make it as strong as you can, if you have the log available.

Jim Rogers