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Author Topic: Beam questions for Post and Beam Structure  (Read 1303 times)

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Offline rodney757

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Beam questions for Post and Beam Structure
« on: August 28, 2016, 11:37:23 AM »
We are building a post and beam structure with strawbale infill. I am having trouble finding formulas for calculating continuous beam size. I have found formulas for simple and double span, but nothing longer.

The building will be 11 x 12. I have seen multiple strawbale builders state that they prefer 6' max spacing between post to give more attachment points for the bales. The roof loads will be 90 psf. My main concern is shear. However I know that strawbale can be load bearing and according to code, they can support 690 lb / ft. I've calculated I need to support 720 lb/ft. So maybe I can use the double span formulas and call it good.

Any thoughts on where I can find continuous beam formulas for shear?


We are located in Western Oregon, near Eugene. The code snow load is 15 psf. We will be putting a living roof, which will add 60 psf. I also included 15 psf for the wood. While I would love to use traditional timber framing, right now we are planning on using steel fasteners. This is a shed roof with rafters 24" OC. The pitch will be between 1:12 and 2:12, still to be determined.

Offline ChugiakTinkerer

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Re: Beam questions for Post and Beam Structure
« Reply #1 on: August 28, 2016, 01:47:35 PM »
Hi rodney757, welcome to the Forestry Forum!  I'm just starting out myself on a cabin build using timbers I cut and mill myself.  There's a lot of experienced and knowledgeable people who will no doubt jump in and offer assistance, but you can probably help them immensely by providing a few more details.  The first one is where are you located?  One reason to ask is to help discern if there is a jurisdictional authority that will want to sign off on a permit or inspection, and the other is to better understand the potential wind, snow, and earthquake issues you may need to address.

Another thing to know, or perhaps clarify, is how your posts and beams are to be joined.  The method of traditional mortise and tenon joinery held in place with wood pegs is referred to as timber frame construction.  Structures built with large timbers but connected with steel plates and bolts is known as post frame construction.  The term "post and beam" is used differently in different places and it may help folks better understand your design needs to know which style of construction you are referring to.

Finally, a few more details on the frame and roof will help determine what the specific loads on your posts and beams will be.  Roof pitch, rafter spacing, roofing material, etc may enable focusing in better on the critical information you're looking for.  A picture is worth a thousand words, so if you can post drawings or pictures that would be great.  Posting images on FF requires uploading them to your gallery, or you can also post a link to an image you may have stored somewhere else.

Oh, have you checked out the toolbox area on this forum?  At the bottom of the vertical banner on the left of the screen is a small red toolbox with a link to many calculators, one of which may be what you're looking for.
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Offline rodney757

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Re: Beam questions for Post and Beam Structure
« Reply #2 on: August 28, 2016, 05:49:57 PM »

Thanks for the suggestions. I updated my post with some more information. I have checked out the toolbox, however I didn't see anything for what I needed. Only simple beam calculators

Offline Don P

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Re: Beam questions for Post and Beam Structure
« Reply #3 on: September 02, 2016, 08:46:21 AM »
Hey folks, popping in for a few minutes and saw this.

I'm a simple guy  :D
It sounds like you've found awc's DA6 here;

From there you can go to the AISC steel construction manual for more extensive beam equations. It isn't cheap but you can usually get it through interlibrary loan.

Simplified Engineering for Architects and Builders goes through three spans.

The Timber Construction Manual, another pricey one, goes through 4 spans... look through their online publications... umm I think
A laborer works with his hands
A craftsman uses his brain and his hands
An artist uses his brain, his hands, and his heart

Offline rodney757

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Re: Beam questions for Post and Beam Structure
« Reply #4 on: September 06, 2016, 10:45:39 AM »
thanks for the suggested publications. I'll take a look at them

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