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Timber Frame Swingset

Started by mjeselskis, June 06, 2012, 09:44:22 PM

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mjeselskis

I can't claim that the swingset it completely timberframed, since I did use a few stainless steel bolts on the top for final assembly,  but the A Frames are all mortice and tenon. I cut the trees (Eastern Hemlock) this winter and pulled them out with the old Case bulldozer. I cut the logs on my LT28 and then proceeded to learn how to do timberframed construction. It's not as easy as some people make it look.

My wife said that she wanted a swingset that the kids wouldnt outgrow. I think this fits the bill. Its 13' tall, and the top piece is 21' long. The top piece is an 8x8 cut to an octagon. Feel free to critique the style, it's the only way to learn.

I put it all up by myself, with the exception of the top beam. My father was gracious enough to come over and lift that into place with his excavator.

The legs are 6x6, the top beam is 8x8 octagon, the angle braces are 3x5, and it's bolted to concrete pillars at ground level. Coated with timbor and thompsons water seal



 



  



 



  



 




 

2006 WM LT28  1993 John Deere 5300
Husqvarna 562XP & 365 X-Torq

ellmoe

   Great job! An interesting project, too.
Mark
Thirty plus years in the sawmill/millwork business. A sore back and arthritic fingers to prove it!

Jim_Rogers

In the first picture you show a tenon with a peg hole.

That tenon doesn't look long enough. What I mean is there is that much relish beyond the peg hole. Hopefully it won't blow out.....

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

mjeselskis

Quote from: Jim_Rogers on June 07, 2012, 07:07:55 AM
In the first picture you show a tenon with a peg hole.

That tenon doesn't look long enough. What I mean is there is that much relish beyond the peg hole. Hopefully it won't blow out.....

Jim Rogers

Thanks for the feedback. That is one of the things I didnt like when i got done and looked it all over. As a result, i used a 3/8" stainless threaded rod at the top of the A to pull it together, to duplicate the strength of those tenons.

For future reference, how much 'meat' should be on the pulling side of the tenon?
2006 WM LT28  1993 John Deere 5300
Husqvarna 562XP & 365 X-Torq

Jim_Rogers

Quote from: mjeselskis on June 07, 2012, 09:09:46 PM
For future reference, how much 'meat' should be on the pulling side of the tenon?

Ah, now there's the question. this one is not just a quick and easy answer.
the answer is "it all depends".....

It depends on a lot of things, and you have to take them all into account.

The engineering council of the guild has done some research on this and it has published some findings and recommendations about it.
It takes a bit of study to figure it out. As sometimes the actual peg hole location can vary. And when it moves the end distance changes.

I believe I have posted a picture of the rules my engineer did for me on a house frame.
Here is a shot of those rules:



These rules are the type of thing that need to be understood and reviewed on a design by design basis.
They may not apply to your design.

On the Timber Framer Engineering Council (TFEC) web site (http://www.timberframeengineeringcouncil.org/index.html) is a library of documents. http://www.timberframeengineeringcouncil.org/library-landing.html

In there is this document called: Commentary to TFEC 1-2010
In this document they explain the information in the TFEC 1-2010 document.
This first document says that you have to figure out the strength of a steel dowel that will equal the strength of your peg first. Then use the steel dowels diameter to figure your offsets from the edge of your mortise and the end of your tenon.
This is a bit complicated and that's why I hire engineers to do this for me.
But in the explain document there is a chart.
And an explanation of the chart.

3.4.8
Edge Distance, End Distance and Spacing
NDS© provisions for edge distance, end distance and spacing in wood connections with dowel-type fasteners are based upon the use of steel fasteners. Since a wood peg has substantially lower lateral load capacity than a steel dowel of the same diameter, the required minimum detailing dimensions (edge distance, end distance, and spacing) to prevent splitting in a pegged joint are less than those for a joint with steel fasteners. One approach to selecting appropriate end and edge distances is to proportion the joint based on the assumption that steel bolts will be used instead of wood pegs. The bolt size is selected such that one steel bolt has the same capacity as one wood peg used in the actual connection. Then end and edge distances are selected based on the steel bolt diameter. Spacing between pegs should conform to the provisions of the NDS© with no adjustment in fastener diameter. The detailing dimensions in Table C3A have been shown by physical tests to develop the full strength of a pegged mortise and tenon connection without splitting of the timber (see References 3 and 5). Use of the provisions of Section 3.4.8 of the Standard may result in end and edge distances smaller than those in Table C3A and may be used accordingly.
Table C3A –Detailing Dimensions Based on Physical Tests
Timber Species End Distance Edge Distance Spacing
Douglas Fir           2D              2.5D            2.5D
Eastern White Pine 4D              4D               3D
Red & White Oak    3D              2D               2.5
Southern Yellow Pine 2D            2D               3D
Yellow Poplar          2.5D            2.5D            3D

In the above chart the D stands for diameter of the peg.

So that's the answer.

I know it's not an easy one to understand.

But that's it.

Here is what it means to me.

First of all, lets look at the joints I did for the house that my engineer gave me the specifications for.

Let's look at a tie beam to post connection. This is one that may have some tension in it, as that's what a tie beam does, it ties the walls to each other and prevents the roof thrust from pushing them out.



Here is a shot of a drawing. My program put a peg centered on the tie beam tenon and I think it was a 1" peg. And I told it to put it 1 1/2" off the shoulder of the mortise towards the center of the post.
This is shown as the green circle in the above picture.

Now, the old school peg placement would have been that the first peg hole be 1 1/2" off the shoulder (of the housing) and 2" up from the bottom of the mortise. And the second peg hole would have been another 1 1/2" over (away from the housing) and 2" down from the top. This is shown by the two black dots, not to scale I just dropped them in to show you this detail.

The problem with these "old school" placements of the peg is that the tie beam is going to shrink. If it shrinks a lot it can not move because the pegs hold it vertically as well as horizontally. And if the top peg holds it up then the tenon is going to split. If the tenon splits then there is no strength there and the peg can get pulled into the crack of the split. This is a big tie beam it is 14" tall and the post is an 8x8. The tenon is a through tenon so it is 7 1/2" long.

Now the engineer followed the rules of the guild and specified that the peg placement be like this:



This is the same joint. 14" tie, 8x8 post, 1/2" housing, 7 1/2" long through tenon.
You can see the first peg is 1 1/2" up from the bottom and the second peg is up 4" from that. This will allow the top of the tie beam to move down when it shrinks. And not split the tenon at the peg hole.
The first peg is 2 1/2" from the shoulder as it is 1" off the center line. And the second peg is 1" over from that which is 3 1/2" off the shoulder. But the first peg is 5" from the end of the tenon and the second higher one is only 3" from the end of the tenon.
I thought I heard one engineer at one conference say that they don't consider the post reduced where the housing is cut. As the long fibers of the post go beyond the housing ends. And that the full width of the timber, on the tie side, be considered the edge distance for the peg hole placement.

To me that second one is too close to the end of the tenon. And to me that means there isn't enough relish there.
But that is what the engineer figured out and that's what was specified in the drawings.
Hopefully the engineers calculations are correct and that this joint will not fail.

This is why joints and designs should be reviewed by qualified timber frame engineers to make these specific design choices.

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

mjeselskis

Thanks for the info. There is alot to it. I've bookmarked this for reference for the next project.
2006 WM LT28  1993 John Deere 5300
Husqvarna 562XP & 365 X-Torq

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