Re: Braces
#4083
03/16/07 02:10 PM
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Joined: Mar 2002
Posts: 1,687
Jim Rogers
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If beerfreak's posts are planed timbers then the layout and cutting of the braces in the center of the posts will work, as he can measure the mortise depth and housing depth (if he's using one) off the surface. But if his timbers are rough sawn then centering brace mortises and housings in the post are difficult to measure and cut accurately. And brace layout accuracy is important for the brace to truly work as it should to prevent racking of the frame caused by the wind. I agree with NH's comments about off center tenons and the possibility of the post being twisted. One solution would be to also center the post top tenon to whatever he is using for a plate. Being an open car port he will have to be concerned about wind up lift and the posts will have to be properly secured to the foundation to prevent any movement due to up lift... Jim Rogers
Whatever you do, have fun doing it!
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Re: Braces
#4084
03/17/07 01:28 AM
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Joined: Jan 2007
Posts: 71
Timbo
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What would be considered to pass shear test , the pegged/ brace itself , or the sheathing ? Also are there different code requirements for agr. buildings? Many old frames are converted for homes and almost all around here use compression braces exclusivly. As I posted earlier we only find it pegged braces in commercial type buildings. My opion is pegs for barns are redundent as nh outlined. But if thats whats required to pass code it would be good to know.
Timothy W Longmore
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Re: Braces
#4085
03/17/07 01:31 AM
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Joined: Jan 2007
Posts: 71
Timbo
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the rough sawn face is not a big deal if you lay out as if it is a hewn beam and cut a house for the brace pocket to be layed-out in.
Timothy W Longmore
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Re: Braces
#4086
03/17/07 01:19 PM
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Joined: Sep 2002
Posts: 67
MTF
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Timbo, My experience has been that a TF relying on compression braces only will not satisfy most building code lateral load requirements. That is wind loads up to 120mph on the coast and towards 100pmh inland, the larger the building, the larger the issue. Using vertical siding to augment the lateral load capacity is a debatable issue; many engineers are not willing to ‘assign’ any stiffness to vertical siding. Some engineers will provide ‘credit’ for SSP’s and most will accept the shear resistance of a pegged brace. Every engineer and timber framer will have a slightly different perspective on this issue, but it is an issue.
My perspective is to add stiffness to a frame when available. Pegging braces is something I’ve always done, I believe it stiffens a frame during assembly, erection and over the life of the frame. I understand that if a pegged brace tenon is asked to carry ‘too much tension’ it will fail. Actually, when frames are loaded to ‘failure’ that is the way they typically fail.
Dick Schmidt has written many excellent articles on this subject, below are some of his results.
Laterally Loaded Timber Frames 2 (March 2002) Fully Pegged (white oak frame) Stiffness = 3270 (#/in) Both Pegs Removed Stiffness = 623 (#/in) The above is for a 2-story white oak frame, the results for a 1-story frame are not quite as dramatic
A very large increase in stiffness is achieved by adding SSP’s. There is not much data available for the increase in stiffness do to the addition of vertical siding, but there is a large increase. There is no data available for the added stiffness do to nailing the siding to the braces, but again there is some.
Read the articles and draw your own conclusions and than build what you are comfortable with and/or what your building inspector will allow!
Not sure why this thread went this far and my apologies to Beerfreak for contributing to the ‘off thread’ discussion.
Thanks, pete
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Re: Braces
#4087
03/17/07 04:00 PM
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Joined: Apr 2006
Posts: 8
P Smith
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It is my understanding that braces are the primary members in any timber frame that allow it to resist racking. Most often from wind. To do this effectively braces are framed in tandem, opposing each other. Thus, when the wind blows on the north gable wall (bent 1) of a frame it would be the braces on the south gable wall (bent 4) under compression that resist the racking effect. Braces were sized and framed to work in compression. Wood is strongest under compression. There are exceptions to this rule but the over whelming majority are meant for compression not tension.
Pegged or non pegged braces. Nailed vs. nonnailed. tenoned vs. untenoned. It seems these demonstrate regional building styles as well as historical transitions. Braces that are nailed throughout a barn/home (often with wire nails) represent the transition between timber framing and "stick" framing.
Why peg the braces if it doesn't work in tension? Because it helps to square the frame up during and after raising. But there are examples of barns where the braces have only stub tenons (I'm thinking of a barn from Ontario I have worked on) I imagine the builder saying:
Forget this there are just two many braces were not going to mortise out 4 1/4" just 2 1/4" and leave it at that. No need to peg them, they won't fall out because as soon as one loosens up the opposing ones "catch" them.
I would thing it would be an interesting study to look at braces, purlin systems, bent spacing, etc. to discover different regional differences. through out the U.S. Ovisouly my experance is with barns from the northeast.
P Smith
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Re: Braces
#4088
03/17/07 04:29 PM
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Joined: Nov 2003
Posts: 1,124
Mark Davidson
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I do not beleive I have ever seen a pegged brace in an old barn in this area(central ontario). Or a brace tenon longer than 3". I have seen plenty of empty brace mortices.... some of the barns around here have only half their braces still in place.
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Re: Braces
#4089
03/17/07 06:25 PM
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Joined: Dec 2006
Posts: 194
E.H.Carpentry
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Don't we all love home/barn owners that decide to remove braces because they seem to be in the way and there also seem to be just to many of them? The frame still holds up but dare you to remove the siding.
Todays siding cannot be compared with the cladding 100 years ago. It is only 1/2" thick at the most. Old siding was 1". So it could very well strenghten the frame even if braces were removed.
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Re: Braces
#4090
03/18/07 01:54 AM
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Joined: Mar 2002
Posts: 1,198
northern hewer
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Well said everyone:
Timberframing as we call it really is Carpentry work using what was available to the builders in years gone by (timbers)
Building buildings using timbers has developed over many generations starting in numerous father lands and finding its way here to NA.
Remember we didn't invent building buildings with timbers, we only rediscovered it lately
nh
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Re: Braces
#4091
03/18/07 01:47 PM
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Joined: Mar 2005
Posts: 77
Ron Mansour
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watching this fantastic discussion unfold has been extremely interesting. I laud you all for your wisdom and willingness to share it. Ron
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Re: Braces
#4092
03/19/07 12:02 AM
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Joined: Jan 2007
Posts: 71
Timbo
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When calculating shear caused by tension in a brace is the peg the only factor considered? A well made timber joint has more strength than just the breaking strenght of the relish behind the peg. A sloppy m&t would greatly reduce the joints strentgh and would fail at the weakist link, the peg if put under tension stress. The system probably still wouldn't fail the opposing brace would still provide substantial support in compression.
Timothy W Longmore
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