Is This Bent Right ?

[Dakota]

This is a one eighth scale model of a cabin that I am in the process of sawing.  The

dementions of the cabin are 24' X 40'.  The first 24' will be normal framing, with the last

16'(great room) being timber framing made up of three bents.  The span on the 1st

bent(next to the stick framing) and the 3rd bent(at the end) will have support posts.  I

want a clear span for the center bent.

I can't understand all those formulas that tell you if the bent is strond enough, so I've

relied on the size of timbers given as examples in the classic books on timber framing,

and added a little girth for good measure.

I'd really appreciate some critique on this bent.  Here's the info:
The wood is ponderosa pine.  All the timbers will be center cut.  The bent will only

support a metal roof(no second level).  Pitch is 12/12.  The timbers are as follows:

rafters = 8" x 10"
collar ties = 8" x 10"
queen posts = 8" x 8"
principle posts = 8" x 10"
tie beam = 8" x 10"
knee braces = 4" x 6"
ridge beam = 4" x 4"
purlins = 6" x 6"

The collar tie/queen post braces will have a 24" run.
The principle post/tie beam braces will have a 32" run.

All advice will be appreciated.
Dakota

[Don P]

Dave,
 I think this is up Jim's alley, I'm comfortable running numbers on the components, I'd like to have him look at the frame as a whole. Either way, where is this going up? Do you know the loads where you'll be?

And last, my memory is terrible, were you an electrician in the Lead/Deadwood area in the early '90's, I think it might have been on Jim Dunn's cabin in Spearfish canyon?

[Dakota]

Don,
I'm figuring 50 psf, even though I'm sure most of the snow will slide off a 12/12 pitch steel roof.

I'm not an electrician, but my son is.  He lives in Salt Lake City, UT though.
Dakota

[Raphael]

  I really like your scale model; if a picture is worth a thousand words then that's gotta be worth a million.
I often wished I'd had something like that when people didn't understand the difference between timber frame and log construction or when SWMBO was having trouble visualizing something in the design.

Do you plan on adding girts between the posts?

  My timber frame engineering comfort level ends about the same place Don's does.
You are at the point where I sent my plans to the engineer for review, something I would have done for the piece of mind even if the building inspector didn't need it.

[Dakota]

Raphael,

Yes, there will be girts between the posts with bracing.  I just wanted to clear up my question on this center bent, in case I needed to incease the size of the center tie beam,  before finishing the model.

Dakota

[Jim_Rogers]

Dakota:
The load of 50 psf, seems kind of lite.
What will be under the metal roof? Boards/planks like tongue and groove?
If you subtract the dead load of the roofing materials from the total load of 50 psf, which could be something around 10 to 15 psf you're snow load would be 35 to 40 psf.
This is why I say it seems kind of lite.
You really should find out what the snow load rate for your area is first before we run the numbers.....
Can you do that?

Jim Rogers

[Dakota]

Jim,

I'll have to do some digging.  I'll be be back when I've got some better information to run the numbers with.
Dakota

[Don P]

I looked up Lawrence co in a pdf I have, it listed 25psf snow load at 4800 ft. That seems low, a homeowners son buried my truck to the windows in a meadow in the northern hills. I saw nothing over 50 psf snow for SD. I'm wondering if the truss plant in Rapid City will have good numbers for your location? We were building nothing special roofwise till up around the ski area, then dropped to 12" oc. It was tough to get my carcass through those  .

[Dakota]

Don,
I've been kind of banking on what my dad did on his cabin that was built 20 years ago at the ranch(same location as my cabin).  We sit at 7000 feet and usually have 4 ft. of snow on the level.  His rafters were only 2x8's, 16" oc.  We've never had any problems with the weight of the snow on his place.  Never the less, I want to make sure that one clear span truss is strong enough.  Good idea about the truss co.  I'll check with them.

Out place is 16 miles south of Deadwood on hwy 85, not too far from Cheyenne crossing.  Have you been up in that area?

Dakota

[Don P]

That was the way we were building there too. Most of the cabins were 24-28 wide, 10 or 12/12, 2x8's on 16's. The one on 12" was in that subdivision on Deer Mt, it was 2x10's on a 32' wide. Did the retired gentleman near the front there finish his scribed log home?

I did jump the gun, I assume there is still no county building inspector?

Coming down from Deer Mt, we would turn at Cheyenne crossing and head down Spearfish Creek towards a Jorgensen built chinked park headquarters and restaurant. The Dunn's place is about halfway between on your left across the creek. It had a green metal roof when I left it. It sheds snow by about 11 am most days.
From Deer Mt down the dirt road from Englewood to Brownsville we built up kind of above the Vol fire dept on that mountain at the Nemo end. Turning down 385 south we did one downstream on Boxelder cr from Roubaix lake. If you look downstream from the little store on 385 at the creek you can almost see the last bend or two into a little hidden meadow along the creek. We almost stayed there. Off the Nemo Rd near the weather instruments on Windy Flats, I helped on that cabin a couple of times and helped build them another across the meadow.

I will say 3 of those roofs have ice dammed at some point since. We're pretty much now doing conventional stick framed cathedrals at 12-14" deep to get more insulation, baffles and airflow up there.

[Dakota]

I can see you've been all over that country.  There are some nice places stuck back in the pines.  I can't believe how fast the area is growing.  Our place is an original 160 acres that was homesteaded.  We are surrounded by the National Forest, so I won't have to worry about someone moving in next door.

I'll be up there sawing the second week of July.  If you're in the area, I'd like to invite you over for a visit.  Let me know.
Dakota

[Don P]

I sure wish I could come in July, my customers are ready to take the wheels off my truck now .

I was at a wood design short course at VA Tech this week and happened to run into two engineers from Rapid City.

If you haven't got anything better to figure with already, those guys figured that area should use 40-45 psf snow load.

[Dakota]

Thanks Don,
I was figuring 50 psf, so I'm glad to get their imput.
Dakota

[Don_Papenburg]

Hey , Is that Diamond T pickup still sitting up on a hill in deadwood ?  Saw it a few years ago  while passing through.

[Dakota]

Well you got me there Don.  Guess I never noticed it.  Knowing Deadwood though, it's probably still there.
Dakota