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Joining two beams

Started by peter nap, January 08, 2008, 06:55:54 PM

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peter nap

I will need to tie two beams together to get the length of the building. I planned to break them on a post but am not sure what kind of joint to use.

I have thought of a half lap on each beam with a pin through them and into the end of the pole or butt jointed using a Simpson bracket that goes into the pole as well as holding the two beams together.

The trusses will sit on the beams.

Jim_Rogers

Peter:
What you're talking about is called a scarf joint, and it shouldn't be over a post.
Do a search here there is lots of info on scarf joints and locations of same here on this forum.
If you can't find it let me know and I'll find it for you...

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

peter nap

Thanks once again Jim. I looked at the glossery and see where there are a number of scarf joints.  When I was boatbuilding they used the term Scarf Joint to refer to a long shallow angled joint to increase the surface area for gluing.

I have a lot to learn :P

peter nap

Hmmm same joint with lips and a wedge.
https://forestryforum.com/board/index.php?topic=15437.0

This is a pretty good one:
https://forestryforum.com/board/index.php?topic=17306.0   ;D ;D ;D

Looks like I have a couple of hours reading ahead of me tonight.
Thanks Jim!




maineframer

Peter,

Scarf joints do not involve the use of glue.  Careful layout, and removal of wood in all the right places will result in a strong and safe (and hopefully pleasing to the eye scarf joint.)Do not hesitate to ask more questions as many people here are reading these posts and are glad to help!
David

Don P

Noticing your location. If its ag use then no worries, otherwise it is inspected. Depending on your inspector the scarf may need engineering where the Simpson Tie would not. Not as sexy but another thought to chase down while designing.

Jim, I'm assuming scarf placement in a 4 post scenario minimum, in the middle bay?

peter nap

It's AG Don...No inspector!

Jim_Rogers

Quote from: Don P on January 09, 2008, 09:16:11 PM
Jim, I'm assuming scarf placement in a 4 post scenario minimum, in the middle bay?

Could be, it really depends on the total lengths of available timber.
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

okie

Jim, please explain why not to position the scarf over a post. The only book I've read on this is the craft of modular post and beam and it states that they should be located over a post for support???
Striving to create a self sustaining homestead and lifestyle for my family and myself.

Don P


Jim_Rogers

I posted a similar story here showing the wave drawing and the graph, but I haven't found it.
If you do a search here for "scarfs" you'll get a long list of threads with lots of info in them. Including these drawings.
Please search this forum as well as read the thread posted that Don is talking about.

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

shinnlinger

Peter,

By your first post I gather you are considering a scarf to get lenght, but are open to other ideas? 

If this is true, I just did a 24x50 frame with a post every 10 ft or so that the 10+ft beams tie into the posts with a tenon.  I only mention this because you can timber frame lenght w/out scarves if you dont' want to deal with them.  Properly done they are a work of art, and you are pullng it off in a barn, so maybe the ideal place to test your skills but if you screw it up they look like crap and can compromise the structure.

You can also of course buy custom beams up intothe 70+ ft lenght, but that is gonna cost ya...
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

Don P

One way I can wrap my head around this is something I've seen in large span glulam structures. Imagine a 4 post span with 3 beams. The outer bays have a beam that overhangs into the center bay. There is then a beam between those overhanging beams. This is all pretty easy to figure, the strengths are all quantifiable.

Going from there to the scarf's wood removal and trying to stay within codebook notching provisions can work if the brace is viewed as a support. If the center beam's notch is less than 1/4 depth at the point it crosses that "support" I think it satisfies their requirement.

This is a good pdf to bookmark for reading on beam design.
http://www.awc.org/pdf/WSDD/C2A.pdf

It has many beam conditions and the formulas to use for each. For this part we usually call the outer beams overhanging the posts a cantilever, the glulam folks call what I've described above a "cantilever system". But! When you look at the beam formulas that term is technically incorrect, this is a beam overhanging a support. As you scroll through the formulas and diagrams, you'll first hit the cantilever math, notice a true cantilever has a fixed end condition, that ain't us. Keep scrolling and you'll get to the overhanging math. Jim's continuous beam formulas and accompanying "wave" moment diagrams are also there.

One other thing to notice is what happens as the loads move around and one or another spans take load while the snow is swept off another, the forces change quite a bit. This is pretty heady stuff for my small brain, which means so far I'd really want an engineer to check it if it is an important structure.

Last, I know a few of you have the AITC Timber Construction Manual. Page 7-165 has several diagrams of "cantilever beam coefficients" to apply to continuous beam formulas to account for splices at various locations.

It is equally possible that I've wandered into a closet  :D.

peter nap

Shinnlinger.....Your right, I'm very open to suggestion ! I've been cutting practice scarf jpints and they are getting better...but cutting two scrap ends is a lot different than cutting full length beams and getting them up there. I have to lift them separately since I'm doing this myself with no crane. I can't put it together on the ground and raise the whole frame at once.

My first thought was to cut half lap joints on the ends and drill and peg the whole thing to the top of the post.

How did you tenon the beams/posts you mentioned?

shinnlinger

Peter,

Here is the best I have handy at the moment



This is for a high posted cape so the posts run above the first floor and the floor beam or eve tie and windbraces lock into the posts and hold it all together.  I threw the nails plates on where they won't be visible and went back later and pegged it all together after tweaking every thing.

NOw I am extremely fortunate that I have easy axcess to a crane, and I assembled the bents laying down and once upright I braced them and then swung the tie with the windbraces  already installed into place.  HOwever I did not have all of my ties ,milled when the crane was here so I had to install some of them later and a buddy and I were able to hoist them in place with a come along and snatch block off a tempory 2x nailed on the top of the posts.

What do you have to help assemble?  A tractor/truck  and block and tackle?  An excavator?  Freindly Neighbors?  I have used all of these to put togehter frames, but have to recomend for safety and ease looking in to renting a crane come the big day.  Around here the rate is $100 an hour with a three hour minimum which aint to shabby if you think about it.
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

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