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Sizing Timbers for 18' x 34'

Started by Rougespear, May 18, 2016, 01:24:06 AM

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Rougespear

Hi all, I don't have a sketch of my plan yet, so I figured this question best belonged here.

I am planning an 18' x 34' timber frame.  I was hoping for some input on structural design, etc.  I am planning a structure with 4 bents with 2 12' bays and 1 10' bay in the centre (2 gables and two intermediates): fir and ponderosa pine timbers = 8x8 posts, 8x10 tie beams, 8x8 top-plates, 4x8 or 4x6 rafters @ 2' OC, and 4x6 braces.  The top-plate will be scarfed over a brace.  Roof will be 12/12 pitch with metal roofing, tie beam joins post 1' below the top-plate, and snow load in my areas is no greater than 30psf.  I was thinking of erecting the frame on top of a conventionally-framed floor with blocking in place to handle the point loads of the posts.

I require NO inspections, engineering, etc.  That being said, I desire a sound structure.

Comments on this initial specification please?  This will be my first timber frame, but I am no stranger to construction and joinery.

Thanks so much!
Custom built Cook's-style hydraulic bandmill.

Jim_Rogers

Have you read this story and see how it goes to determine timber sizes?

https://forestryforum.com/board/index.php/topic,50714.0.html

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

Rougespear

Thanks Jim... an amazing discussion of "how-to" engineering!!  The only thing I did not grasp was what is an acceptable amount of beam deflection?  I am assuming less than 1/4"?  It is unfortunate the discussion never progressed to joinery design.

I think I can follow along and do the calculations and then I can report back here with more definitive information.
Custom built Cook's-style hydraulic bandmill.

Jim_Rogers

If you use the calculator in the red tool box it will tell you if the beam passes or fails. The requirement is 1/360.

Read the "how the calculator" works explanation story.

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

Rougespear

Design loading for a loft: what is a typical specification for psf loading in a loft used as an office area?  I see a typical second floor is 40 psf.  My planned 16'8" span 8x10 tie beam won't carry the loft load of 40psf + 15psf (dead load) where bent spacing = 12' O'C.  I wonder though: when designing a loft under a 12/12 pitch roof, where only the central 7-8' will potentially receive full loading, should the total loading on the tie beam be reduced to reflect this?  For example: the central 8' would be calculated as 40psf, and the outside 4' sections directly under the roof calculated at 20psf (or less)?

Further, is it more appropriate to specify the loading of an "office area" loft as 30psf?  However, the timber still fails to "pass" even at 30psf.
Custom built Cook's-style hydraulic bandmill.

Jim_Rogers

If you reduce the span then the load is reduced. You could do that with the support wall or add a post.
If you don't want to add a post you'll have to increase the depth of the tie beam. Or change the type of wood to a stronger one like red oak or something like that.

We normally use 10 lbs for dead load of flooring for second floor loads. 40 lbs for second floor office loft sounds about right.

You asked:
Quotewhen designing a loft under a 12/12 pitch roof, where only the central 7-8' will potentially receive full loading, should the total loading on the tie beam be reduced to reflect this?
I don't normally do that. We figure the entire area.

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

Rougespear

Thanks Jim, I think I'll carry the load with a stick-framed wall underneath.
Custom built Cook's-style hydraulic bandmill.

scriber

When using the beam calculator should I be using the unsupported beam measurement between the posts or the total length measurement of the beam?

Rougespear

I'm pretty sure we have to use the unsupported span, which is the true "span".
Custom built Cook's-style hydraulic bandmill.

Jim_Rogers

Quote from: scriber on May 25, 2016, 01:35:14 PM
When using the beam calculator should I be using the unsupported beam measurement between the posts or the total length measurement of the beam?

Unsupported beam means just that. The length of the beam that is unsupported. That means inside the vertical posts. So if your building is 18' wide or 216 inches you need to subtract the two posts. If the posts are 8x8 then you need to subtract 16" (8" x2) That would be 200 inches or 16.67'

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

Rougespear

Custom built Cook's-style hydraulic bandmill.

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