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Re: Timber Frame Design #5109 08/18/03 11:34 PM
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Emmett C Greenleaf Offline
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All thanks to Ed L, the post bottom to concrete issue has been solved forever. Hinges with plates the same size as the post bottom, Moisture barrier material between the hinge/post AND the hinge/concrete. Net add to vertical height about 2" so set your concrete 2.5" below the subfloor and your will never see the seam. Was used for the Mountain School Barn just completed. Kinda makes kids work of raising the bents too. Lotsa labor and material savings. Conversationally the 8x8's used in Vershire, VT ran "about" $50.00 a copy. Added paranoia relief by welding them shut after raising.

Re: Timber Frame Design #5110 08/19/03 09:42 PM
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Paul Freeman Offline
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As one would expect, Ed's solution is ingenious and simple. I'm compelled to add the caveat that this may not satisfy "hold-down" requirements. A hinge flap secured to the bottom of the post might simply be secured by screws into end grain...not very yielding against pull out. However perhaps used in conjuction with a product like those offered by www.timberlinx.com (similar concept to furniture barrel nuts) and a hinge would be satisfactory... Although the hinge and bolt head maybe a problem, perhaps timberlinx would offer a tapered bolt head, and the hinge might have countersunk holes.... In this case I would weld, in the prior case welding seems comforting, but I have little faith the hinge would be taxed before the screws pull out of the end grain.

Re: Timber Frame Design #5111 08/20/03 05:40 PM
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Kurt Westerlund Offline
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I don't understand what the hinges are for. I think you can get all the uplift resistence you might need by ensuring proper embedment of the t-rod or sstb into the conc. and observing NDS specs for dolt dia's from end of piece. If you need more value, double up the timerlinx or barrel bolts.

Timberlinx look nice because they only use a 7/8" dia expansion thing which can be easily covered by a 1" dia peg. Also they can be tightened down for proper takeup of any "slop"

Most folks doing "timber style" (not timberframe) construction around here use a custom "embedment plate", basicly a simpson CB replacement made with 1/4" steel and a bolted, internal kerf plate. (2) 3/4" machine bolts usually attach the post. The kerfs are usually not seen on the sides and are cut freestyle with a chainsaw plunging into the end grain.

HTH

Re: Timber Frame Design #5112 08/21/03 01:20 PM
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Jim Rogers Online Confused
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If you would like to see some photos of this "hinge" plate check out this post on the Forestry Forum/Timber framing section:
http://www.forestryforum.com/cgi-bin/board/YaBB.pl?board=tframe;action=display;num=1060266331
There are a couple of photos of this hinge there, which I took. Also check out the schools photos of the barn raising at:
http://www.mountainschool.org/program/barnchrono.htm
At the time I posted the photo of the "hinge" plate, I didn't know who designed or invented them. But Emmett was there and has told us that it was Ed Levin the frame's designer.
I'm not sure how deep the bolts go into the concrete but there were some drawings that showed "J" shaped bolts embedded in the concrete for hold-downs of other sill boards. Jim


Whatever you do, have fun doing it!
Re: Timber Frame Design #5113 08/24/03 04:41 PM
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Ed Levin Offline
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Some clarification on the Vershire Mountain School hinged post bases. The panel screws from upper plate into post end grain are only locators. The real base-to-post connection is an inch and a half vertical pipe (1.9-in. o.d.) welded to the upper plate and inserted into a two inch diameter hole in post end grain. The pipe is, of course, invisible after installation.

In addition to horizontal restraint, this pipe can also provide hold-down capacity via a horizontal bolt/pin through posts and pipe. We did not bother with this in Vershire since structural analysis indicated that barn dead load exceeded predicted uplift by a safe margin (discounting any help from the vertical siding nailed to mudsills anchor bolted to the foundation).

Upper and lower hinge plates were welded together after the raising (the reason for the originally unpainted parts of the fixtures). Lower plates were bolted to the foundation with four three-eighth inch Hilti HVA adhesive anchors, two of which could easily handle side load or zero gravity uplift.

To my knowledge, there is no capacity for illustration on Ask the Experts, but I would be happy to supply PDFs of the shop drawings for the hinged bases. Or perhaps Jim Rogers could post them at his Forestry Forum Website? For future discussion there is a much more elegant prototype hinged post base on the drawing board waiting for an appropriate project.

Re: Timber Frame Design #5114 08/26/03 02:36 PM
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Jim Rogers Online Confused
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Ed:
I'd be happy to post anything you'd wish me to post for you. Jim


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Re: Timber Frame Design #5115 08/26/03 10:15 PM
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Jim Rogers Online Confused
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Here is a drawing of Ed's hinge plate design used at the Mountain School barn project.
As mentioned in Ed's post the bolt threw the pipe was not needed.
Ed: Thanks for the drawing, hopefully this will help others to understand how it could be used. Jim


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Re: Timber Frame Design #5116 11/24/04 02:11 PM
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gib Offline
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I've re-opened this thread because I am going to be building a very similar timber-frame structure. After reading the replies, I need to re-think how I am going to attach the posts to the concrete footers. I was just going to embed the post in the concrete, but I think I will stay away from that. Does anyone have any more to add on this subject?

Also, I will be using an 8x12 tie beam and king posts, 8x10 rafters, and 8x8 purlins. The discussion of "overkill" came up, and I am certain it applies here. I am more concerned with having too much weight from the rafters and purlins than would cause structural problems. I like the classic aspect of timber-framing "over-building. Being an open-frame design, I would like to end up seeing a "sturdy" structure complete with aspects of traditional joinery. But I certainly don't want to build something that is structurally unsound.

Does anyone have any thoughts on using 8x10 rafters with 8x8 purlins for a northern Wisconsin application?

Thanks, Tim

Re: Timber Frame Design #5117 11/24/04 04:51 PM
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daiku Offline
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Tim:

8x8 purlins do sound like overkill. What is your roof pitch, rafter spacing, and proposed purlin spacing? CB (in Northern Minnesota)


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Re: Timber Frame Design #5118 11/24/04 06:03 PM
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Paul Freeman Offline
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Tim:

Well, first of all you are absolutely correct not to embed the posts into the concrete. Not only should untreated wood not be embedded, it simply should not come in direct contact at all with concrete as it will rot. As pointed out prior in this thread, a yoke or some other metal fastener is most appropriate in this situation.

Your second question should be answered when you have your frame engineered. It is not possible to determine whether it is overkill without establishing the loading of the timbers. Specifically the wind and snow loads, the pitch of the roof, and the spacing of the bents and purlins. In addition you will need to provide the species of the timbers. These questions will resolve timber sizes for bending, any point loads can further impact your size choices. Once you have the size established then you need to determine your joinery. It is not uncommon for the joinery to need a timber that is larger than that required to carry the load.

That said, if we assume Oak (midwest) and 40-50 psf snow load (CABO), 10 psf dead load (shingles on panels), 48" purlin spacing (panels), and a 15'6" bent spacing then your purlins would need to be 8x12 and you would still have close to a 1/2" deflection. So failure is the issue, not overkill! However, if you reduce the bent spacing to 11'6 then a fully dimensioned oak 8x8 would just barely work, nominal fails, that's how close it is. As long as the purlins pass over the principal rafters with minimal notching you might pull it off. Watch out for horizontal shear, shear kills more designs than bending. Unfortunately the 8x10 principals appear to be woefully underdesigned before beginning to address the joinery.

Don't forget bracing, wind loads, and other factors such as roof materials, and "low roof" conditions. There are also some signficant joint loads at the bottoms of the principal rafters, and possibly at the top and bottom of the king posts. This is only an opinion and is by no means an accurate engineering analysis. But as I said at the opening, your engineer will answer all of these questions for you.

These forums are wonderful for discussing these questions but they can not be used as a means of saving money on engineering fees. In the long run the costs resulting from a poorly designed frame greatly exceed the modest fee of an experienced timber frame engineer.

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