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Load calculator-where to find it on this forum?

Started by pizza, February 14, 2019, 09:09:32 AM

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pizza

Hi. Just joined the forum today. Where can I find the load calculators everyone speaks of on this forum's website?

Jeff

In the toolbox.  Under the forum's extra tab. There is also a toolbox to the left of the page on a pc under the sponsors on desktop, or the bottom of the page on mobile. Welcome to the forum.

One slice or two?;)
Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

pizza


maple flats

Welcome to the FF, pull up a log and sit a while. I'm not one, but there are experts on here in every thing you may want to know about a forestry or equipment related question.
logging small time for years but just learning how,  2012 36 HP Mahindra tractor, 3point log arch, 8000# class excavator, lifts 2500# and sets logs on mill precisely where needed, Woodland Mills HM130Max , maple syrup a hobby that consumes my time. looking to learn blacksmithing.

pizza

I was looking at the "INPUT" table for the Uniform beam load calculator for 2-4" lumber and was confused by the "size" input field because to the left of that is a beam width, beam depth and span inputs. So what is the "size" for? Thanks 

Jeff

Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

Jim_Rogers

Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

pizza

In other words, I'm trying to size a beam, that my roof rafters will rest on (called the "plate" I believe). This beam will be using 3.5" wide lumber (4 by material) since the posts that are supporting it are 3.5" x 3.5" pressure treated posts. I just had a large pin oak (which is in the red oak family) cut down and thought I cut use that for the plate material. I even might be able to get all of the posts and plates out of this tree, I'm considering that too. Thereby eliminating the need for that lousy pressure treated stuff. This structure is going to be a small wood shed. Footprint is 87" front-to-back x 99" left to right, 3.5" square posts at each corner. Each bent will run the 87" long direction. The roof overhangs 10" at the gable ends. It's a gable roof. That beam will be 84" long plus 16.5" plus 16.5" for a total of 117" long. 
This little project is my foray into timber framing using 3.5" material to start.

Should I use a different calculator for that?

I attached my drawing below

 

Don P

Hey Pizza, welcome to the forum.
Yup you are using the correct calc, I should probably relabel that input and make it clearer. It is correctly called "size factor" and adjusts the bending strength. The size input you would use is 2x4, I should relabel that as 4" wide, etc.

The inputs in blue adjust the design values according to duration of load, size factor, repetitive member, wet service and whether or not the lumber is incised. Those adjustments are then made to the base design values by the calc and used as it checks the member. Look at the very bottom table of the calc after you do your inputs and notice the base design values in the left hand column and then the adusted design values in the blue column. Then go up and change the size and hit "show result" again and notice what it does to the adjusted design values. With any changes to the inputs in blue it changes those adjusted design values which in turn changes your allowable member strength. That has all been worked out by the smart folks in labs after testing many samples to destruction.

So for duration you would have snow, repetitive no, size 2x4, wet no, incised no. Oh and species, pin oak is grouped under northern red oak. Make sense?

Edit;
http://forestryforum.com/members/donp/ddsimplebeam.html
I made some changes. That input is now labeled "size factor".

I complicated it a little bit, something I intended to do when I made it, it might make it a little more confusing. The adjustments for width are different for 2&3" thick lumber than for 4" thick material. I had just used the 2&3" thick numbers originally which is more conservative for several widths and the same for others. I just added the 4" thick part of the table which gives a 10% bump in bending strength for 4x8-4x14 and wider.

There is a design problem with your roof, this is a small structure and I doubt it is a problem but something to think about as you build wider spans. As load comes down on the rafters the feet push outward, rafter thrust. You need something to either tie the rafter feet together or at least very low in the roof tieing across the rafters, or, hang the rafters from a ridge beam.

pizza

Wow! Thanks so much! Much much appreciated.

Yes I realize that about my roof and intended to tie the plates together to prevent the spread out from the roof load.

In the table for "Load on beam (pounds)", do I assume that since this table is titled as "Uniformly Loaded Simple Beam" that the load number means a uniform load in lbs per lineal foot? Or should I calculate it in pounds (from my calculated load in pounds per lineal foot x my span, shown below)?

I've calculated my uniform load (pounds per lineal foot) on the top of one wall to be 256 plf (pounds per lineal foot). I arrived at this from the following:

Uniform Load (lbs/sq.ft) x tributary width (ft) = Uniform load (lbs/ft, plf)

My uniform load (lbs/sq.ft) for my area of SE Pennsylvania is Live load (30psf) + Dead Load (15psf) = 45 psf

My tributary width (for half the roof) is 5.69 ft.

Therefore my uniform load on the plate for the one wall is 45psf x 5.69 ft = 256plf

Would I put this number in the table or do I put 1792 lbs (256plf x 7ft (my span)) into the load in that table? 

Thanks





Don P

Ah, another label I should probably clarify better. The Total uniformly distributed load on the beam, 1792 lbs.

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