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Author Topic: How to make clear span using 8x12x20 white pine?  (Read 349 times)

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Offline rmallaire

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How to make clear span using 8x12x20 white pine?
« on: October 08, 2017, 07:44:09 am »
 

  The attached picture is similar to the middle bent I want to have in a 20x24 high posted cape.

 I would like to use what I have. I have an 8x12x20 white pine beam that I want to use as the tie beam in the middle bent of a two bay 20x24 frame without a center post, making a clear span. I am drawing plans for a 20x24 high posted cape, queen truss, half loft. 13 8x8 posts, allowing for a 2 knee wall.   I want to use all of the proper bracing so that my building inspector will approve the plans of using an 8x12x20 tie beam without a center post.

When using the beam sizing calculator on the forum, when I input 5,000 for total load and 2,000 for dead load it passes. But when I input 10,000lbs for total load it fails.  Therefore, I am trying to create additional support with bracing.

My wording of this may sound confusing: I want the tie beam 10 above the floor, so I am fine with using longer compression braces below the tie beam such as 4/cos45= ~58  (giving 4 of vertical and horizontal component).

Aside from the 45 degree braces below the tie beam in compression, I would like to use tension braces coming off the queen posts. I have access to a metal fabrication shop and I was thinking of using 1 diameter steel stock with threaded ends, to connect the queen posts to the tie beam using 3 washers and nuts. As the brace above the tie beam that connects the queen post to the tie beam at 60 degrees above the beam, I thought steel would better suit this instead of wood.  With it primed and painted high gloss black, I personally think it would be aesthetically pleasing too.  This may be putting strain on the principal rafters for the middle bent so I am also considering what size they should be (would 8x8s be large enough)?


Any and all help would be appreciated. Thank you.
Randy
John Deere 970 tractor with several attachments, Massey Ferguson MF200 dozer

Offline Roger Nair

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Re: How to make clear span using 8x12x20 white pine?
« Reply #1 on: October 09, 2017, 07:12:07 pm »
Rmallaire, to my thinking you are on the right track with a queen post truss, however what you have illustrated is not sufficient as a design to account for the needs of the roof system.  The truss could be the primary roof support with either a common rafter/principle purlin system, common rafter/ridge beam system or a principle rafter/common purlin system.  That choice needs to be made before a truss and the gable bents can be designed.  The loft floor load will need to be loaded onto the queen posts, likely by means of metal gussets, etc.  Third the illustrated  rafter tie should likely have to change position, lowered between the heads of the long struts and become a straining beam.  If you were considering rafter couples with a tie, I think that would be a weak stressful choice.
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Offline rmallaire

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Re: How to make clear span using 8x12x20 white pine?
« Reply #2 on: October 10, 2017, 08:26:21 am »
Hi Roger, thank you for the reply. I was planning to use common rafters.  I will draw the bent, showing the rafter tie lower. Should the rafter tie, queen posts and struts all intersect at the same location? In regards to the metal gussets, are you referring to the use of angle iron being bolted to the queen posts and tie beam?
Randy
John Deere 970 tractor with several attachments, Massey Ferguson MF200 dozer