Suggestion of what wood joints to use?


I am building a reasonably large 'open barn' style, car port/garage ... 6.6m wide x 8.6m long. Open on front & one side, where construction will be using bolt down base plates for 150x150 vertical wood posts, these will run up to a Glulam beam that runs horizontal. The posts will have 80 x 8mm thick steel plate Y brackets for intermediate posts and knee brackets for corner posts.
There will be an angled piece of wood 150 x 150 in section running upwards 'gallows' bracket style to fix horizontally to Glulam. The steel plates bolted either side of & thru these and the vertical post.
I would like to 'let' the gallows bracket into the vertical; post and the horizontal Glulam, is there any specific joint that is used for this ? The post is thicker than Glulam width, and will be stepped to allow Glulam to 'rest' on top of post as well as be bolted to it.
If difficult to visualise there are 2 pics of this on :
http://www.esnips.com/doc/8ca0d1b9-a479-4d60-8dac-1a9e2f4e3113/Centre.jpg
or http://tinyurl.co.uk/7955
http://www.esnips.com/doc/91a7192e-5787-4f4e-a831-a5ca8aa8117a/Knee.jpg
or http://tinyurl.co.uk/w6j9
I don't want to weaken either the post or the Glulam.
Glualam & Posts are in pre3ssure treated softwood.
The 2nd part to this is, should I also think of a joint between top of the post and where it meets the horizontal Glulam beam... thought about using some 30mm thick dowels, make the holes with a little play for ease of lining up and fix with expanding polyurethane glue ... would fill any gap.
http://www.esnips.com/doc/4b07e0ea-c359-41b3-a04d-ba50bc37e93d/post-top-fix.jpg
or http://tinyurl.co.uk/rluq
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I'll leave the rest for others, but just will comment on the choice of glue here. Do NOT mistake the foaming of polyurethane glue for a gap filling glue. Yes, it fills the gap, but with a foam that has very little strength. For a gap-filling glue, you are much better off with an epoxy of some sort.
Of course, if I interpreted your drawing correctly, gravity is holding the two pieces together, and the pegs are providing alignment and resistance to sheer forces. The glue would only be used to prevent the roof from lifting up off of the pegs, and if you have a weather event strong enough to lift the roof, the marginal resistance of a little glue on the dowels is probably not going to make much difference.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

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You seem to have a detailed and well thought through design already.

the width of the glulam. Structurally it looks fine, 150mm square posts have a massive capacity (unless very tall). Are you expecting any unusual snow or wind loadings in your location?
As I understand your questions, you're considering inlaying the mild steel brackets? Presumably by the 6mm bracket thickness - you're doing this just for aesthetics? Posts and braces would be fine, but I wouldn't bite into the width of the beam. You could always have a central beam in a saddle joint with 30mm shoulders, rather than the single 60mm shoulder (150 - 90mm) of the drawings. The shoulders are only spacers for the steel brackets.
You're also considering vertical location dowels - these seem superfluous, unless they help with construction. I'd go for 10mm stainless pins if anything, again less material removed from the beam.
Overall I'd aim for least drillings in the beams, which will be bearing much greater stress than the posts
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No but the posts had to be this size to support tile loading ( a few ton up there), and particular in conjunction with steel brackets to provide racking strength (wind load on frame)

No ... my explanation must have been poor. Am bolting the steel plates either side of the post/gallows bracket .. through bolts, what I wanted to do was just to joint the wooden angle pieces into the vertical pot and Glulam ... I guess mainly for aesthetics, and it would look better thn ajust a cut end ... not only protceting the end grain, but the wood will shrink back in time and it would then give a visible 'gap' (OK not much) but if jointed in it wouldn't happen.
- you're doing

Could you explain this a bit more, don't underatnd what a saddle joint is.

Good idea ... cheers
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I think you're describing mortice and tenoning the joints at both ends of the wind brace. This what would be done with traditional green oak post & beam construction. But they use draw-dowelling to tighten the whole thing up (the holes for the pegs are drilled slightly off-centre, so hammering the pegs home tightens the joint - essential because of the srinkage of green oak)
In your drawings, the wind braces are already housed slightly into the posts. Ideal to provide support without removing too much material from either post or brace. If you mortice and tenoned. you'd be removing a third of the thickness of the post (tenon usually one third the thickness of the timber). However I'd be more concerened about removing any material from the beam.The existing design (already approved by Building Control?) is again ideal with the small bolt holes to secure the brackets to the post and braces.
I guess you could use the same technique to house the wind braces slightly into the beam as you do with the posts - but I wouldn't do it. You'd be notching the beam on the underside where it's in tension - and it's really difficult to get tight, accurate joints on windbraces on both ends at the same time.
In reality no timber will be perfectly straight with no twist whatsoever (the glulam may be pretty close) and you're more likely to end up with a gap from day one!
Much easier to build as the drawings show - cut the windbraces slightly overlength, offer them up to the already erected post and beam - and trim to fit! Clamp them in place - then drill for the brackets in situ - best chance of everything fitting tightly.
As far as shrinkage opening up the butt joints goes, isn't kiln-dried softwood going to be pretty much dimensionally stable?

A saddle joint is like a mortice and tenon, where the mortice is open like a fork end, so it just "saddles" the tenon.
I was suggesting that as an alternative to the half-lap joints that are currently shown in the drawings to match the posts and braces (150mm) with the beam (90mm).
Currently you cut away 90mm of material from the top ends of the posts and braces, and the reamining 60mm wraps up one side of the beam. You could instead make that 30mm wraping up either side of the beam. The beam then sits in the "saddle" or "forked end" of the posts and braces - and you still don't cut away any material from the beam.
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Doh! I've been saying "saddle" when I mean "bridle"! (I knew it was something to do with horses).
For the sake of clarity: http://en.wikipedia.org/wiki/Bridle_joint
Other joints here: http://en.wikipedia.org/wiki/Category:Joinery
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snipped-for-privacy@gglz.com wrote:

Thanks for that ...
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Osprey wrote: > I am building a reasonably large 'open barn' style, car port/garage > ... 6.6m wide x 8.6m long. Open on front & one side, where > construction will be using bolt down base plates for 150x150 vertical > wood posts, these will run up to a Glulam beam that runs horizontal. > The posts will have 80 x 8mm thick steel plate Y brackets for > intermediate posts and knee brackets for corner posts. > > There will be an angled piece of wood 150 x 150 in section running > upwards 'gallows' bracket style to fix horizontally to Glulam. > The steel plates bolted either side of & thru these and the vertical > post. <snip>
IMHO, this is basic construction, not furniture building.
The steel plates carry the load at the joints.
Letting those plates into the wood will only create stress concentrations and weaken the joint.
Foaming glue is a total waste of time and money, especially in this application.
The bolts maintain registration so dowels are not required.
Treat it like the engineered construction project it is and have fun.
Lew
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On 8 Sep 2006 10:37:04 -0700, Osprey wrote:

To my eye the notch type joint you have already looks fine but I dispense with that heavy, ugly, steel plate and but a stopped mortise and tenon inside the notch with a peg all the way through to hold in place.
At the top of the notch it would be the start of a champher down to the base of the bottom notch rather than a step as you have shown. Top of the vertical, stopped mortise and tenon with a peg again.
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Dave ... No can do ... the structural calcs don't work for wood alone ... it fails on racking strength when the computer programme applies the shear wind loading. My original desire was straight forward wood gallows posts .. mortice & tennon joints, but when you feed the figures into the programmes it fails, especially on wind loading.
The steel for this is costing me a fortune - I wish I could avoid it.
I spent a lot of time with some structural Engineers to try and get it to work in wood and couldn't get it to pass the calcs. The issue is I have 3.6m clear spans between the posts, (which I required to get my boat in) ... if I reduced to 2.4m then it could have been done in wood.
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For heavy timber construction a kind of joint is used which looks like through-bolted but actually has a steel ring cut into each member to hold the shear forces. The ring is invisible (buried in the wood) when assembled.
The only way to make it look esthetic, though, is to glue a mahogany hexagon over the bolt head...
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Rick Hughes wrote:

Well of course it will. It'll probably fall down too.
If you want to build a timber structure like this, talk to a real framer like http://structuralcarpentry.co.uk/ and have them explain "wind braces" to you. If you don't have some diagonalisation in there, even small ones in the corners, then racking will topple it in no time.
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On Fri, 8 Sep 2006 22:46:39 +0100, Rick Hughes wrote:

Use bigger and/or stronger wood... 150mm sq ain't that big. You have model to play with, would 300 sq cut make it or 200 but a hardwood.
Softwood is not what I would term a structral timber, now a nice bit of green oak on the other hand. Ah, hum, steel with knotty pine is probably cheaper... oh well.
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Dave Liquorice wrote:

Didn't want Oak ... as I want to stain the wood to match the timber used on the house ... and unless you specifically want the 'oak effect' it's very expensive.
The cost of an Oak beam to span across 7.5m ... out of my price league.
I have alreday had all the steel shoes & brackets made so can't change the section size ...
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