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Author Topic: Post and beam with a dab of timberframe - a necessity  (Read 550 times)

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Offline Ionel Catanescu

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Post and beam with a dab of timberframe - a necessity
« on: January 23, 2018, 05:31:20 AM »
Hello everyone.

I'm new to posting here but have studied timber construction for a long time and the info given by people on this forum has been very valuable to me.

First, i'll give you a small background so you may better understand what i'm about to explain.

In my neck of the woods (eastern Europe), building with wood has become a pretty crooked experience
Skilled and knowledgeable people are almost an extinct species.
This is true for those that design in wood and those that build with it.
Also, actual timber quality is skydiving besides the fact that you can't get any member larger than 8" by 6" (actually it's 7 1/2 by 5 1/2).

Timber building is mostly relegated to roofs and those who build in "wood" are actually making stick houses where everything is held together by OSB.

After helping my godsons wrap a "wood frame" in strawbales some years ago and observing it's performance, i decided that this is what i want to build.
And what's a more suitable structure for this than timberframe ?

Well, all is nice and well but timberframe cannot be, but it's close relative, post and beam, and here's why:
- lack of labor, skilled or not - i'll have to do it by myself, maybe having 1 or 2 extra people to help, mainly in lifting;
- lack of time - if i am to cut and install all joinery, i'll be having white hair alround - i need to finish the frame by this summer - in a 2-3 week vacation from the dayjob
- small timber sections, enough to do some basic jointing but not enough for the more elaborate ones.

So, since my PE has put metal brackets in the design (a very basic, spartan, design), i have them already ordered and delivered.
My structure is held together with these:

But there are some places where these fall short.
One of them is beam splicing.
The PE recommended half lap over a post but i'm not that happy about it.
I have studied again my options and, from a volume of work / performance perspective, i have come to understand that a stopped splayed undersquinted scarf is more appropriate as it's much better in shear and twist resistance.
The most simple fixing is with 1/3" lags, 4 of them, to fix the 2 parts together for tension resistance.
A wedge can be used but, even in it's most basic form, it will take extra time cutting  the channel.

So, i have drawn a sketch on an exterior wall (parallel to the ridge, the rafters go above the top beam, perpendicular to it) that show how i imagine the scarf joint.
I can't place the scarf exactly on top of the post as the lag bolt (3/8 by 4") that is used for the angle brackets will have to engage enough wood to be effective.
Also, if jointing exactly above the post, i would be throwing away a little over a foot from each of the almost 17' long beam and have the middle beam be longer.
All this leads to waste that i don't like.

Orange are transversal, weight holding beams (the sill is 6/6 and the others are 8/6), yellow are posts (6/6) and green are longitudinal (tie) beams, same size as orange ones.
Red are 4/6 floor joists and brown green are roof rafters.
Not all braces have been included in the drawing.


Please share your thoughts on this matter as i have some more jointing related questions.

Thanks in advance.

Offline Don P

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Re: Post and beam with a dab of timberframe - a necessity
« Reply #1 on: January 23, 2018, 06:32:46 AM »
I'd want to see more drawings, I'm not really understanding this. You can also put bolsters on top of the posts or across 2 posts under the beams and splice above the bolster. When you investigate the splice you can look at it optimistically as a continuous beam. You can also look at it as 2 beams overhanging posts that are merely in contact. The truth lies between those views.

Offline Ionel Catanescu

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Re: Post and beam with a dab of timberframe - a necessity
« Reply #2 on: January 23, 2018, 07:00:47 AM »
Hi Don.

Here's the aerial view of the sill plate.


And a section thru Axis 1


The first picture i posted is a section thru Axis A.

Regarding bolsters, i could use them but they'll complicate the fixings.
I'll have to fasten the bolsters to the post and the beams to the bolster :
With the connectors i've shown - in which case i wouldn't have enough of them ...
Or with some joinery - which might take a lot of time to do.

Offline Ionel Catanescu

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Re: Post and beam with a dab of timberframe - a necessity
« Reply #3 on: January 26, 2018, 06:34:31 AM »
I've looked again at my drawings and i see some interesting things:
- the ridge beam is butt jointed over posts;
- the plates (from gable to gable - transversal beams in my images) are jointed over posts, no splicing details provided but most probably it's a half lap
- the tie beams (longitudinal in my images) are half lap on edge over posts.

None of this really makes me feel confident even if the PE says it's fine.
My gut feeling says i can do better that this.

I've read all the info abut not placing a splice over a post but over a brace.
Like over here


Due to my design and member lengths, most convenient location would be either over posts or a little off them.

For the plates, the most convenient place is between the posts closer to each other.

But the distance between them is about 2'.
If i place a scarf here. there's no more place for a brace.
Should i leave it be or put a small (maybe 2x6) bolster underneath and put some lags there ?

For the ridge beam, the most convenient is to either but over posts, maybe with a bolster, or splice it as the plates.

For the tie beams, i'm not sure how to proceed as i really don't want the splices over the posts.

Offline Don P

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Re: Post and beam with a dab of timberframe - a necessity
« Reply #4 on: January 28, 2018, 04:28:28 PM »
I can't say any of this is passing my gut reaction but it is up to you to satisfy yourself.
Informationally, these are some coefficients for various cantilever systems. It assumes a hinged connection and locates the point of inflection better than just "over the brace". Remember however as loads get into the real world that all starts to fall apart anyway. An engineer friend said he left that stuff for others. He was less concerned in a roof than a floor but didn't specify it in either location, even in steel. He was a little less diplomatic  :D I've put this in my gallery, I think you can save and zoom it. I think this would be considered fair use to this discussion.

For a much more detailed explanation the AITC TCM manual goes into more depth in chapter 7, end of the beam equations. I don't see that section online in a free download; http://aitc-glulam.org/shopcart/index.asp



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