hello

I rebuilt an old corn barn this last summer. it was three bend so not very big. In the center bent I put a collar tie. I opened up the barn the other day and the collar tie was on the floor.

? is. What is out there to replace the collar tie with something in compression instead of in tension . but can only go rafter to rafter.

iamm thinking an X

have a good day
heath enright
pinegrovehewing co.

Hi Heath;

Collar beams are almost always in compression. If you can't spend time getting creative trying to put a collar in after-the-fact, maybe you will need to violate the frame with some nails!

Jim

If the colar was on the floor, wa-hapen? Did the walls move out? Tim

I was under the impression that collar ties don't hold the walls together, but instead serve to keep the rafters from sagging and thereby actually increase the possible wall spread. Is this right? Would someone educate me? Thanks in advance.

My guess is that the collar tie was too low!! If it is at the top third like it should be it will be in compression!

Carlos

Unless there is nothing else to tie the walls ...


Are there any tie beams in this building?

How could it fall out? How was it attached? Definitely need more infor for these guys. A picture is worth 1000 words.

ill put some pic up thurday of the barn

We want pictures!! We want pictures!!

hear is a pic (you might have to turn your head)

http://pic50.picturetrail.com/VOL399/10944455/19463401/312891204.jpg

Heath --

That collar is in compression -

How is it joined to the rafters ? Is there any other sign of movement in the Barn ?

Where in Maine is it located ?

Do consider posting your sense of what are the norm in historic framing typologies in your area to this thread - >

http://www.tfguild.org/forums/ubbthreads.php?ubb=showflat&Number=15056#Post15056

Here's the pic turned and enlarged.

Hard to see much in the picture of the joint or the rafter feet!

Carlos

Hi Carlos,

We cannot see in the photo whether or not there is a dropped tie or crossbeam in place between the main posts but I rather suspect probably not and so if this is the case then the collar will be operating in tension since there is no other tension member preventing building spread.

This doesn't look too good to me.

Regards

Ken Hume P.Eng.

Will, I see a lot of that roof type in Down East Maine. We also have common rafters.

Heath, put a cable in at the eve line and move on. The collar was doing nothing. That looks like a lot of roof for no tie member. I am wondering what the second plate is all about? The one with the fresh post under it. If that is what it is. Tim

good day

the second plate made two walls, an inter which was straping, the outer wall had vents from the 2nd floor about 3 ft up along both side of the corn barn. We think to dry the corn.

i learned alot from this barn like

every side board was a lap joint on top and bottom with a 45 dag bevel at the top so any water would shed away.

all the clap boards were over laped 4 to 6 in. insted of just butted agenst each other.

get the hewing thing down

heath enright
pine grove hewing co

Heath, how much structure was involved with the inner wall? I am wondering if its structure made a wall system stiff enough to withstand the thrust of the roof. Tim

Hey everyone,

So if there is no tie anywhere in the arrangement, then no matter where you put the collar it will be in tension?

If there was a tie below the plates or at the plates (don't know if this would make a difference with the collar arrangement) at what point does the collar move from compression to tension? Is it at the midpoint of the rafter?

At the gable ends of the pictured structure are the studs negating thrust? And will the spacing of the bents with the ridge add more load to the middle bent with the collar?

Sorry for all the questions. This seems like crucial stuff.

Thanks, mo

tim

well this is what i got

there is a main top plat and a secondary top plat that holds up the iner wall.

now the secondary to plat has a tie beam mortis into that beam and then goes on the top of the main top plat like any english tie joint.

i wanted to make this building histoic as posible the only thing i did differnt was put the collar tie in.

The collar tie is an add on after???

Mortise and tennon? It would be imposible to put a collar tie in properly after the fact!!

How did you install the collar tie... more pictures would be helpful of the actual joints as much as possible.

Carlos

Mo,
Just a carpenters perspective,
Take a stiff birthday or Christmas card and set it on a table as a "tent" or gable roof. Push down on the ridge, the rafter feet slide out, there's the thrust.

Using a needle and thread make a tie across the bottom and repeat the test. You have made an immutable triangle and proven the tie is in tension since thread doesn't work in compression.

Now move the thread tie halfway up the card and repeat. At the same load the rafters bend and begin to thrust again.

Move the thread up to just under the ridge and load again, I'll bet you have thrust and tear out of the card at the connection.

For the barn in the picture,
If there is just the one tie then it is in tension. In that case the leverage against the tie would make it tough to connect and it would put large bending force on the rafter below the tie. As the tie approaches the plate the forces drop off. I think in the red book it states that a tie should try to be within a foot of the plate. In the IRC rafter span tables it gives a span reduction for conventional rafters as the tie is raised to account for the rafter bending forces.

If you already have a tension tie and then wish to brace the rafters then this raised tie would be in compression. A kingrod with struts might be a better option.

If you do not make a strong triangle of rafters and tie then the ridge should be designed as a beam supporting that section of roof. Yes, the studs are essentially propping the ridge at the gable.

If the tie is below the plate then the thrust from the rafters puts bending forces into the posts, the post is then not just a column in compression it is a column with a combined bending and axial load, this reduces its normal axial load carrying capacity.

Pinegrove's description of the 2 plates with a short section of "tie" between them is neat, never seen that. I guess the pair of beams are helping each other to resist the thrust from building corner to corner. It must be quite flexible to have dropped the new tie, but has obviously held up. I'd sure want a cable or something from rafter foot to foot or turn the pair of plates into a horizontal trussed girder. I guess neither is historic.

Don P. i think you got it in the last paragraph. This is a historic building, am I right Heath? If so here is historic proof of this being done. The done part is the Horizontal Trussed Girder. It's like using a 8"deep by 30" wide plate to resist thrust. This is my suspicion. I like the card test.

As for the studs in the gable ends, if you removed them the wall would not move out the rafter may sag a bit(compression) but the wall will stay put, it has a tie. The middle bent has no tie to speak of other than the theoretical HTG. This building is not all that wide. Heath how wide and long is this building and number of bents? I am wondering if you noticed any bow in the wall at the eve line before you rebuilt it? Did you completely disassemble it, and move it to a new location? Is there a bow now? Tim

Your collar probably fell out because the walls are spreading. I think you need to tie the walls together at the plate level. I would measure from outside of plate to outside of plate and see how much it has moved.

How wide is the barn?

If you need to bring the walls back together, you will probably need to lift the ridge while you pull the walls together. All pretty hairy stuff, unless you know what you're doing. Once the walls were back plumbish, I would install the traditional repair for spreading walls -- tie rods. All approved by an engineer, of course.

Good luck, and keep us posted.

ps I didn't see that several others have already said similar stuff before I posted.

Don's example is a good one. Doing something to resist wall spread is something to think about. Perhaps this was originally designed such that the weight of the roof was considereed low enough relative the wall stability that they didn't tie the walls? Of course everyone will feel better having a tie beam.
One thing that I can't tell from the pic is how the collar tie is attached to the rafters? Was it just nailed up? Is there mortise and tenon and pegs? Calculations could be done using the dimensions, and estimated loads to estimate how much force is being applied to the top plate from the rafters. This would help you size a tie beam and how many and what size pegs to use. Depending on what your intensions are. You could also use a steel rod as a tie if you don't want to go to the truble of a tie beam and don't care about historical accuracy.

the tie was mortise in and pegged


closer look

it was my fault when i drilled for the peg i only had a 1/2 in of meat on the end of tenon.

we had about 4 feet on the roof and 50 mph wind


so i think just setalling of the new hewn side/ we jack and leaved the build put grant back in for a foot so it dropped a little

thank you all for the help

heath enright

I don't see anything tying the plates together in the photo. I would assume your walls spread and failed the connections of tie to primary rafter. It looks like you need to install some ties closer to the plate or external flying butresses.

good day

well the corn barn has two top plats one for the outer wall and one for an inter

their is a tie beam on each side connecting the double plats

i thought a collar tie on the rafter would work

i am just going to put a comalong on the first purlin bring it back togather.

thanks for the help
heath enright
pine grove hewing co

Heath, why not put the come-along in the plates plane? The first purlin will take more force to bring it back. Tim