Need some help with calculation for a timber frame open gable patio cover

[ChrisZTT]

Good evening all. I am new to this forum but so glad I stumbled across it.  I was trying to use the beam calculators to figure out if my patio cover is going to fall on my head but can't quite figure out how to use it and was hoping some of the more experienced people here could give me a hand.

My project is going to be an open gable stacked timber patio cover. I dont plan on using collar or rafter ties. I am not going to do jointery on it except were the roof rafters connect with the gable beam, otherwise just lagging it together. Stack will be a post, side beams directly on top and lagged in, then gable beams on top of them and lagged. Info is below:

No snow, I live in Foslom, California.
The structure will be #1 doug fir. Roof decking will be pine.
The 4 posts will be 8x8" x 9' tall bolted onto a concrete footer. On the gable end facing my yard will have a 32" over hang so post to post along the side will be 10'. Not sure of the post to post length on the gable end but should be around 17' (18" in from each end).
The beams on all four sides will be 8x8" as well as the kings posts and ridge beam. The gable end beams will be the 20' section. The ridge and side beams will be 13 1/2' long.
Overall size is 20' wide at the rafter tips. The depth 13 1/2' gable to gable.
I also plane on using 6x6 braces at the corners and next to the king posts.
Roof rafters will be 2x10" spaced 24" apart with a 6:12 roof pitch.
Decking will be 1x6 tongue and groove.
Not sure if I want to do shingles or metal roof.

Any help would be greatly appreciated. Thanks in advance

[Jim_Rogers]

Which timber do you need help with?

Jim Rogers

[ChrisZTT]

The beams are what I would like to check. I wanted to make sure the 8x8's could handle the span, particularly the gable end beams with a stretch of about 17ft post to post. There will be some 6x6 braces in the corners which will shorten that span up a bit more to maybe 14ft. I was also hoping someone could verify the ridge beam will be bulky enough to stop any rafter spread since I would like it to be an open vaulted roof.

[Don P]

Hey Chris, welcome to the forum. At least for myself I've proven the word picture doesn't work. Can you sketch and dimension something and post it?

[ChrisZTT]

Here is a quick sketch. Hopefully it works. 

 

 

[Don P]

Chris, we are talking about something similar in this thread now;
http://forestryforum.com/board/index.php?topic=106958.0
Read it and decide if you are waning to build this as a truss supporting a ridgebeam or a crown posted ridgebeam support.

[ChrisZTT]

I went through the other post andthere are similarities but the big difference is I want to use solid timbers and he is looking at built up members. The example pictures are very similar to what I am looking at doing. For the calculators, I can't figure out were some of the numbers you enter for the calculation are coming from.

[Don P]

The question in my mind is whether the gable beam is a post supporting beam or not.

Reference which calc and which numbers are giving you trouble, walk me through an example and I'll walk you back through it.

[ChrisZTT]

In my drawing the gable beam is supporting the king post at mid span which in turn supports the ridge beam if that's what you mean.

And for the ridge I just realized I would like the rafters to at least match in depth so would a 2x8 rafter work for an 8x8 ridge beam or should I increase the ridge beam to a 8x10 or 4x10 to match a 2x10 rafter.

The numbers I am unsure about are

Load on Beam - Im assuming this is calculated by 1/2 length x width of roof x dead wt of about 20?
Maximum Allowable Fiberstress in bending - no clue
Modulas of Elasticity - no clue
Maximum Allowable Horizantal Shear - no clue

Load on Beam(pounds)
Span of Beam (inches)
Width of Beam
Depth of Beam
Maximum Allowable Fiberstress in Bending (PSI)
Modulus of Elasticity (million PSI)
Maximum Allowable Horizontal Shear (PSI)

[Don P]

Your king post is really a crown post which is center point loading the gable beam, reread that discussion in the other thread. Built up or solid is not the distinction, where I was going is truss or beam. Either is fine just need to clarify what the load path is.

Total load is dead load, I'd call that 10 lbs per square foot + live load, code minimum is 20psf, so 30psf.

Check the ridge beam.
tributary length 10' post to post
trib width 8.5'
10' x 8.5'=85 sf
85 sfx 30 psf= 2550
use the heavy timber simple beam uniformly loaded calc;
http://forestryforum.com/members/donp/beamclc06b.htm
live load 2550, dead load is 10psf x 85sf=850lbs, span 120,width 8, depth 10, #2 dougfir beams and stringers, hit show result and it'll fill in the design values, write these down for later.
More than enough, you can play with dimensions to tune that up.

The ridge load on the crown post;
For ease call the overhang 3' and half of the ridge from crown post to crown post, 5'. So a tributary length of 8'. Half of the roof load between side plates is bearing on the ridge, 1/4 + eave overhang is bearing on those plate beams. So trib width is half of 17', 8.5'.
8' of length x 8.5' of width=68 square feet loading the gable crown post
68 sf x 30 psf=2040 lbs
Open the center point load calc;
load 2040, span 204 (braces do not reduce span, banish that thought), width 8, depth 8, design values from above, Fail. Bump it up to 8x10 passes.

Check your plates with the uniformly loaded beam overhanging one support calc. trib length 10' x width 4.25' + 1.5' overhang and proceed.

 I'm off to change planer knives, drying in the haybarn seemed like a good idea, grinding blown dirt now doesn't seem so good  :, 2 sets of knives yesterday. Holler if you get stuck.