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Author Topic: opinions on kingpost variations  (Read 17409 times)

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Offline Thehardway

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opinions on kingpost variations
« on: August 02, 2006, 10:27:44 PM »
Interested in opininions on the two forms of kingposts as illustrated below,  Which is best and why.  Also interested in any ideas on what joints would be best for building the raised bottom chord truss pictured below in the Rafter to bottom chord / tie beam area.  What is the arched block under these joints called? Is it technically a brace?.  Also, does anyone know what joint would have likely been used in the 32' Kingpost truss pictured on pg. 110 of Chappells 'A Timber Framers Workshop' for joining the tie beam to the kingpost. It uses a two peice tie beam from the looks of it. Thanks.





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Offline Raphael

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Re: opinions on kingpost variations
« Reply #1 on: August 03, 2006, 02:58:01 AM »
  It's kind of hard to say which is 'better' without knowing what the rest of the truss is going to look like, the expected loads and the exact geometry of the joints...  (PS: Your pegs are high in both illustrations).
  I'd say the one on the left is better because it leaves more meat in the top of the king post without reducing the strength of the rafters or their connection to the king.  And the one on the right is better because the geometry is simpler so it's easier to cut a good snug joint.

I'll have to get back to you on the Chappell illustration as my copy isn't handy.

Quote
What is the arched block under these joints called? Is it technically a brace?

I'd call it a Corbel which is a kind of brace.  But it may have another name when used in that position.

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Offline scsmith42

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Re: opinions on kingpost variations
« Reply #2 on: August 03, 2006, 08:54:39 AM »
THW - nice looking work on the truss in your pix!  Scott
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Offline Thehardway

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Re: opinions on kingpost variations
« Reply #3 on: August 03, 2006, 09:28:50 AM »
Let's assume the kingpost is being used in a truss like the one in the picture rather than as kingpost bent.  Loads are 20 psf live 10psf dead, pitch is 12/12 and span is 24'  intersections would therefore be at 45 or 90 degree angles.   Trusses are 8' OC. What joints would you use?  Placement of pegs would be corrected based on wood type (in this instance Chestnut Oak) and timber dimensions (9"D X 7" W ) as well as whether or not a ridge beam was used.  I see where you get a corbels. I thought corbels were for cantilevering or supporting projections from a vertical surface at 90 degrees like a bracket only one peice and usually embellished with some sort of architectural detail but don't know why they couldn't be used in other applications so I will call it a corbel at least for the purpose of this post or until corrected otherwise.

PS. Scott, I did not build the truss in the pic. It is just an example for discussion purposes.  I wish I knew who did build it to credit them but I can't find the source of the pic. I do like the lines and the raised chord however and would like to replicate them on my own trusses.  I beleive there were a couple other board members interested in raised chord trusses a while ago.
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Offline Raphael

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Re: opinions on kingpost variations
« Reply #4 on: August 03, 2006, 11:55:12 AM »
I usually think of a Corbel as being at a post and beam junction (first TF example I saw was internal for tying and floor support vs. external for a cantilever), but it seems to fit the example better than pillow or shear block...  I guess it's a bit of both but it's also a bit of a cruck. ???

From memory I believed the two piece tie beam in the Chappell book (pg.110) was splined, good thing I kept my mouth shut.
  On closer examination I don't see any pegs and I believe I see wedges (in two different planes) passing along the tops of the tie beams through the king post which would make the joinery a half dovetail at the ends of the tie beams.  Makes sense as the wedged dovetails will resist rafter thrust better than the pegs through a spline will.

For your truss I'd go with the simpler (right hand) example, the other would be used when the tie is also carrying a significant floor load.
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and the truth hit him like a man with no parachute.
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Offline Thehardway

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Re: opinions on kingpost variations
« Reply #5 on: August 03, 2006, 04:52:53 PM »
Here is the basics of what I have so far
Top of Kingpost



Bottom of kingpost with non/continuous tie-beam  using shouldered, wedged, half dovetails offset from both sides.  (I am aware this is not as structurally sound as a continuous beam and I will use preferred continuous beam if timber selection allows)


I also just found the forum post on wedged half dovetail joint for kingpost in which Jim addresses this issue directly.  If I understand him correctly the splined joint illustated below might be a good option as well?  In it the tie beam actually is housed in the post mortice along with the spline to support the weight of the tie beam with the post rather than the spline and pegs supporting it. The spline is left to perform in tension only to prevent rafter spread. It also helps to prevent shear and deflection.  I am not sure about peg size or placement nor the exact length the spline should be.





I am working on drawings for tie beam to rafter including "corbels" and will post soon.  Any glaring errors here?  All drawing will be submitted for engineers review/stamp just want to do as much of the pre-engineering as possible (with the help of the board of course).

Here is an additional picture showing a truss utilizing a half-dovetail joint for rafter to tie/beam connection

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Offline Jim_Rogers

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Re: opinions on kingpost variations
« Reply #6 on: August 08, 2006, 10:27:06 AM »
First of all, I don't understand this drawing:


If the one above it is a side view is this a top/plan view?



If that is suppose to be the king post in plan view it really doesn't look right to me.
And in the other king post drawing it looks the same and it doesn't seem to be right.
Hopefully you can explain it to me so that I can understand what's going on there.

Also, I know Steve Chappell personally. I've been to his school many times.
I'm hoping to go up there next month, and I've just called him to ask what type of joint he did use on the king post to interrupted tie beam in the workshop truss, but he was not in and I left him a message.

When I get an answer about this I will post it.


If I don't get an answer, I will look at it when I'm there next month

Jim Rogers
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Offline Raphael

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Re: opinions on kingpost variations
« Reply #7 on: August 08, 2006, 01:14:29 PM »
First of all, I don't understand this drawing:
(Image hidden from quote, click to view.)

If the one above it is a side view is this a top/plan view?

(Image hidden from quote, click to view.)

I stared at that one for a while before I figured out what he was showing us.  He's got the beams in plan view and the king in side view to show the mortice, since the king is only 7" deep my brain kept trying to make it another beam...
... he was middle aged,
and the truth hit him like a man with no parachute.
 --Godley & Creme

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Offline Jim_Rogers

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Re: opinions on kingpost variations
« Reply #8 on: August 08, 2006, 04:40:45 PM »
Ok, well in the future proper labeling would help to understand these kinds of things.....

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Offline Thehardway

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Re: opinions on kingpost variations
« Reply #9 on: August 08, 2006, 05:41:12 PM »
Sorry Guys,  original drawing I did was labelled but when I converted it to a JPG or gif for upload it dropped the text for some reason >:(  Raphael is correct. Beams are plan view, post is side view.  It is basically a shouldered  through mortice in the kingpost with the bottom angled in opposing directions to accept the angled bottom portion of the half dovetails (shown in post plan view).  The tennons are offset to allow a half lap splice within the kingpost.  I guess this is a case where the words were worth a thousand pictures?  I will try to fix the drawings Jim, my apologies. 
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Offline Jim_Rogers

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Re: opinions on kingpost variations
« Reply #10 on: August 09, 2006, 09:11:50 AM »
On the way home from the roast, I stopped at a friend's house and looked at some plans he had of a project he was working with his client on.
Here is a shot of the king post to interrupted tie beam with splines:



Due to the reducing factors this is very hard to read.
I'll create another drawing showing it and try and post that.

Or if someone wanted to see this in a larger scale they could email me and I'll return an email with the larger version of the photo.....

Jim Rogers
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Offline Jim_Rogers

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Re: opinions on kingpost variations
« Reply #11 on: August 09, 2006, 10:25:09 AM »
See if this is any better:



Well, I guess not really.....

I you need to see it drop me an email.....

Jim Rogers
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Offline beenthere

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Re: opinions on kingpost variations
« Reply #12 on: August 09, 2006, 11:14:20 AM »
Jim
I've noticed most of your pix are reduced to 350 pixels, rather than just to 400 on the long side. That additional reduction makes them harder to view, and am curious why you don't leave them larger?   ???

You post a lot of great pix of details, and sure appreciate the information you pass on. Don't mean to sound like I'm complainin' here.  :)
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Offline Raphael

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Re: opinions on kingpost variations
« Reply #13 on: August 09, 2006, 11:38:45 AM »
I'd try saving it as a gif if you have that option.  They are obnoxious for photos but ideal for simple diagrams as there is no compression loss.  It may not help the text much at these sizes but the lines will be sharper.
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and the truth hit him like a man with no parachute.
 --Godley & Creme

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Offline Jim_Rogers

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Re: opinions on kingpost variations
« Reply #14 on: August 09, 2006, 02:12:46 PM »
I thought the rule was 350 for the width.....

Here is another shot of the same drawing as a gif file with 400 pixel width:



I don't think this is much better.....

Jim Rogers
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Offline beenthere

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Re: opinions on kingpost variations
« Reply #15 on: August 09, 2006, 02:58:44 PM »
It's 400 pixels, but this last one is only 5kbyte, which is pretty fuzzy.

I've no suggestion how to fix, as I don't know the original format or a possible font size increase to make it more readible. But think that 400 pixels and 30kbyte will be acceptable as an image on the FF.
 I find that adjusting to the 400 pixel dimension and then saving to lowest compression works better than compressing first, followed by pixel dimension.  Just don't ask me "why?"  cuz I don't exactly know :)
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Offline Furby

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Re: opinions on kingpost variations
« Reply #16 on: August 09, 2006, 04:25:45 PM »
I can try and explain that one Beenthere.
When you compress, you are averaging the pixels in the pic. so there is less info in the file size. By bringing it to 400 pixels and then compressing, your size stays as you need it and those pixels are then averaged.
If you compress and then adjust the pixel width, you are in a sense pulling the averaged pixels back apart to get a wider pic (or taller), thus you distort the end results.
Tom has a better explaination around here someplace.

Offline Max sawdust

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Re: opinions on king post variations
« Reply #17 on: August 09, 2006, 08:55:34 PM »
Jim,
Could you PM me the full size image of the spline?  I am very interested in the spline.  I decided not to use a hammer beam truss but to use a two piece tie beam on my tractor shed.  I was thinking of the 1/2 dovetails to king post as mentioned above and in Steve's book or your Spline idea. 
My gut tells me the spline would be stronger ;)
Max

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Offline Max sawdust

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Re: opinions on kingpost variations
« Reply #18 on: August 09, 2006, 09:12:52 PM »
On closer examination I don't see any pegs and I believe I see wedges (in two different planes) passing along the tops of the tie beams through the king post which would make the joinery a half dovetail at the ends of the tie beams.  Makes sense as the wedged dovetails will resist rafter thrust better than the pegs through a spline will.

On page 90 he makes it quite clear (to me ::)) that he uses half dovetailed and wedged tie beam to kingpost joinery ???  read the caption on the photo on page 90...
The photo is of the library at fox maple school.  quote un quote :D "Half dovetailed and wedged tension joinery is used to join tie beams to king post"

I am trying to decide on a spline or Steve's example,
Jim? why are you against this joint?  (If you are?)

I posted this question a month or so ago, and no one seemed to know what I was asking.  (Which would not surprise me since I am kinda dense Midwesterner ;D)

I do not understand "east coast" timber frame politics, I just believe you east coasters know quite a bit about traditional joinery   Not sure if this two piece tie beam idea is a new one and debated or if our forefathers found lasting ways to use a two piece tie beam through good engineering and experience ;) 

Max
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Offline Raphael

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Re: opinions on kingpost variations
« Reply #19 on: August 09, 2006, 11:04:30 PM »
On page 90 he makes it quite clear (to me ::)) that he uses half dovetailed and wedged tie beam to kingpost joinery ???  read the caption on the photo on page 90...
The photo is of the library at fox maple school.  quote un quote :D "Half dovetailed and wedged tension joinery is used to join tie beams to king post"
<snip>
Max
The stupid midwesterner :(
Dunno about the stupid part, you figured out the answer might actually be in the book.  While I just guessed from what I could make out in the picture. ;)

I like both joints, they are both good strong solutions when properly applied.
If I was going for the fine homes look I'd want to contrast a Walnut spline and pegs against chamfered white oak beams.  Otherwise I like the artistry of the joinery in the wedged dovetails so it's what I'd choose to cut.
... he was middle aged,
and the truth hit him like a man with no parachute.
 --Godley & Creme

Stihl 066, MS 362 C-M & 24+ feet of Logosol M7 mill


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