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Top plate scarf location

Started by stevensam, August 18, 2010, 08:49:42 PM

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stevensam

Hello,

I'm slowly cutting a Dutch style barn as per Jack Sobon's design in 'Timber Frame Construction', page 171.

I'd like the frame to end up 32'x40' but at this stage I'm flexible on the length and have cut most of the main posts.  The longest logs I have access to are 17' and I'm trying to figure the best way to frame the scarf locations for the top plates.  All posts/plates are 7"x7" and thinking of using an edge halved scarf with bridled butts and located above a brace joint.



   

I'm not sure if the middle section has enough support, does anyone have any ideas?
Much appreciated,

stevensam

Here's a rough model of the 32'x30' barn.  A few braces are missing and looking at adding another bent to make it 40' long.


Mad Professor

I've never seen a a scarf placed directly over a knee brace.

Jim_Rogers

Your scarf locations are correct, over the braces for support.

I have written a story about scarf joints, including the reasons why and posted it here on the forum.

You could/should find this story and read it.

A while ago, I designed a small house frame and the engineer who reviewed my frame design suggested that I place my scarf joints as you have them.

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

shinnlinger

 The brace will support the scarf, but it might be  tricky joinery/cutting to get a mortise in there  depending how you are going to do it.  Jim might have some more insight on this, but I believe traditionally they would offset the scarfs a foot or so from other frame elements to simplify such a key intersection.  Your scarf/mortise design will be key.

Another question/suggestion is what is the barn to be used for?  Less than 10 ft between posts is a little tight for pulling machinery in and out.  My barn's  main door opening is a full 11 ft across and I wish I had gone to at least 12 quite frequently.....  Like when backing in a hay wagon or even just pulling my dually trucks in.

Dave
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

Raphael

I agree the spacing on the posts might be a bit tight if you want to allow traffic to cross through in that direction.

The center of the scarf in my laundry room is tweaked outward from the post.
Partly due to the rough length of timber I started with, but it also allowed more meat to set that brace mortise in.


The joint also got three pegs that weren't installed yet in this photo.
... 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

stevensam

Thanks for the replies and info.

I had a tweak of the model and made some changes, 12' bents for total length of 36'.  In this format the scarfs will be over the posts and will use 2 less posts than going 40' with 10' bents.

Also, the barn will be used for a wood working shop.




stevensam

I've searched through the forum and rethinking having the scarfs above the posts.

Looks like a new model will be needed.

kfhines

Stevensam,
looking at an earlier post, the model with the two men in it. It looks like the floor joist are cut into the top of the Anchor beams you might want to rethink that. Cutting into the top and sides will drastically reduce the section of the beam. In the pictures I've seen of old Dutch Barns if they had a loft or second floor the floor joist were laid on top of the Anchor beam. Some thing to think about. FWIW I would also agree with the scarf joint over the brace.
  Your models look great. I have a thing for the Dutch Barns and would like to build one for my next project.

kfhines

Dave Shepard

The scarfs are located over the brace as that is the lowest stress area in the plate. Jim, do you have Jack's diagram of the stresses in a plate? I thought I saw that around here somewhere. I've been in this barn/garage, it's about 15 minutes from me. In fact, I have all of the floor joists and planking in my shed, as it is was picked up and moved across the yard and put on a slab.

kfhines, look for a pm re: Dutch barns.
Wood-Mizer LT40HDD51-WR Wireless, Kubota L48, Honda Rincon 650, TJ208 G-S, and a 60"LogRite!

Jim_Rogers

Quote from: Dave Shepard on August 23, 2010, 05:04:40 PM
Jim, do you have Jack's diagram of the stresses in a plate? I thought I saw that around here somewhere.

Yes, I sure do, it's in a thread about scarf location and it includes the timber wave drawing..... smiley_wavy
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Jim_Rogers

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

Aikenback

I have a question for you Jim, considering your extensive experience. would not the joint location depend on (among other things) the length of the beam, and the relative lengths of the span in question and the adjacent spans? the knee brace would not necessarily fall anywhere near the optimum point regarding bending and shear.(aprox. 1/4 span i believe). I assume the theory is that the knee brace is at least closer to that location. I would think that any joint in any location will change that graph to some degree. It's never too late to get an engineering degree i guess. Comments?

Cheers 
no whining.

stevensam

I made a couple of changes as per the suggestions, thanks.
In the first two models there is a short connecting plate in the middle of the span.




In this model the top plate has three similar sized plates located above braces.


Any ideas in which is the most suited design or should I add an extra post as in the first post??
Also, I'm really impressed with Google SketchUp!

stevensam

Quote from: kfhines on August 23, 2010, 06:41:27 AM
Stevensam,
looking at an earlier post, the model with the two men in it. It looks like the floor joist are cut into the top of the Anchor beams you might want to rethink that. Cutting into the top and sides will drastically reduce the section of the beam. In the pictures I've seen of old Dutch Barns if they had a loft or second floor the floor joist were laid on top of the Anchor beam. Some thing to think about. FWIW I would also agree with the scarf joint over the brace.
  Your models look great. I have a thing for the Dutch Barns and would like to build one for my next project.

kfhines


That's something to consider, I had planned 4x4x2 pockets for the floor joists on the 7x14 anchorbeam.  I think on the Dutch barns the second floor was used for hay storage which had considerable weight?  I would likely use the second floor as an office.  It would be just as easy to lay the joists on top to maintain the anchorbeam strength.

laffs

soooo what if someone put a scarf in so that it landed between the post and the brace ??
and what if someone already boarded it over and it cant be changed ??
would someone be alright by doing that ??
timber harvester,tinberjack230,34hp kubota,job ace excavator carpenter tools up the yingyang,

jamesamd

Better add bolts through,that unsupported scarf.Laffs

Jim
All that is gold does not glitter,not all those that wander are lost.....

Jim_Rogers

Quote from: stevensam on August 24, 2010, 06:48:11 AM
Any ideas in which is the most suited design or should I add an extra post as in the first post??

When you have to figure out where a scarf should be located; there are some are some facts you need to take into consideration. Such as, but not limited to, is this a hand raising or a crane raising? What is the longest piece of timber you can afford to get? Which end of the building will be raised first? last?

Sometimes the answers to these questions will help you to determine where the scarfs are and in which position the laps are so that it can be assembled.

This is one reason why some people make models of their frames and experiment with the raising schedule, sequence or sometime called script. Knowing which order that these things will be assembled helps to understand how the scarfs are going to go together and what length they will be.

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

Jim_Rogers

Quote from: Aikenback on August 24, 2010, 01:46:23 AM
I have a question for you Jim, considering your extensive experience. would not the joint location depend on (among other things) the length of the beam, and the relative lengths of the span in question and the adjacent spans? the knee brace would not necessarily fall anywhere near the optimum point regarding bending and shear.(aprox. 1/4 span i believe). I assume the theory is that the knee brace is at least closer to that location. I would think that any joint in any location will change that graph to some degree. It's never too late to get an engineering degree i guess. Comments?

Cheers 

It's very hard for me to give you a direct answer. Each frame design has to be reviewed for all the facts I mentioned in the last post I just made above this one.
And besides all that other factors such as roof loads, floor loads, and wind loads have to be taken into consideration.

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

stevensam

Thanks Jim for your time and thoughts.

I'll think about the points you raised and design the top plated from there.  Hopefully pictures to follow soonish.

Regards,

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