Help: Posts sizes for an Oak framed garage

[ATTAK Z]

MintSprint said:

ATTAK Z said:

You can have posts and rafters as big as you like but the building will still fail if you don't take account of overall stability and good practice in jointing the members.

This is perfectly true. It's invariably racking stiffness that's the biggest problem with post-and-beam frames, and that's only ever going to be as good as the connections (joints).

[singlecoil]

ATTAK Z said:

MintSprint said:

ATTAK Z said:

You can have posts and rafters as big as you like but the building will still fail if you don't take account of overall stability and good practice in jointing the members.

This is perfectly true. It's invariably racking stiffness that's the biggest problem with post-and-beam frames, and that's only ever going to be as good as the connections (joints).

I expect Mint meant to mention the braces as well.

[MintSprint]

singlecoil said:

ATTAK Z said:

MintSprint said:

ATTAK Z said:

You can have posts and rafters as big as you like but the building will still fail if you don't take account of overall stability and good practice in jointing the members.

This is perfectly true. It's invariably racking stiffness that's the biggest problem with post-and-beam frames, and that's only ever going to be as good as the connections (joints).

I expect Mint meant to mention the braces as well.

I didn't actually think it was necessary to mention them. Braces are just one of the structural members that are connected by the, erm, connections. They kind of go without mentioning?

And you don't always use braces to provide the racking stiffness, of course. Do I get marked down for failing to mention all the other components that contribute to the structure?

I was merely agreeing with ATTAK Z that there are two fundamental elements to any framed structure: one is the structural members, the other is the connections between them. If either one is inadequate, then the whole structure will be inadequate.

[ATTAK Z]

MintSprint said:

singlecoil said:

ATTAK Z said:

MintSprint said:

ATTAK Z said:

You can have posts and rafters as big as you like but the building will still fail if you don't take account of overall stability and good practice in jointing the members.

This is perfectly true. It's invariably racking stiffness that's the biggest problem with post-and-beam frames, and that's only ever going to be as good as the connections (joints).

I expect Mint meant to mention the braces as well.

I didn't actually think it was necessary to mention them. Braces are just one of the structural members that are connected by the, erm, connections. They kind of go without mentioning?

And you don't always use braces to provide the racking stiffness, of course. Do I get marked down for failing to mention all the other components that contribute to the structure?

I was merely agreeing with ATTAK Z that there are two fundamental elements to any framed structure: one is the structural members, the other is the connections between them. If either one is inadequate, then the whole structure will be inadequate.

[MintSprint]

ATTAK Z said:

Do you have a point, ATTAK Z, or do you just drink a lot of virtual coffee?

[ATTAK Z]

MintSprint said:

Do you have a point, ATTAK Z, or do you just drink a lot of virtual coffee?

Just happy to be associated with the experts

[singlecoil]

MintSprint said:

singlecoil said:

ATTAK Z said:

MintSprint said:

ATTAK Z said:

You can have posts and rafters as big as you like but the building will still fail if you don't take account of overall stability and good practice in jointing the members.

This is perfectly true. It's invariably racking stiffness that's the biggest problem with post-and-beam frames, and that's only ever going to be as good as the connections (joints).

I expect Mint meant to mention the braces as well.

I didn't actually think it was necessary to mention them. Braces are just one of the structural members that are connected by the, erm, connections. They kind of go without mentioning?

And you don't always use braces to provide the racking stiffness, of course. Do I get marked down for failing to mention all the other components that contribute to the structure?

I was merely agreeing with ATTAK Z that there are two fundamental elements to any framed structure: one is the structural members, the other is the connections between them. If either one is inadequate, then the whole structure will be inadequate.

Well, in the context, mentioning them probably would have been a good thing, as you know, it's all about triangulation, or as much of it as is possible (and necessary). But the rest of what you said is, as you already know, perfectly correct. I just mentioned the braces for the sake of completeness.

[MintSprint]

singlecoil said:

...it's all about triangulation, or as much of it as is possible (and necessary).

Well, as much as necessary, certainly. A post-and-beam frame is never triangulated as much as possible.

Traditional timber post-and-beam frames (I'm avoiding the phrase 'oak frame', 'cos we do a perfectly serviceable line in Douglas Fir!) aren't designed as fully triangulated structures in anything like the same way that a spaceframe for a car is. The braces just provide localised stiffening of the post-beam connection (which is why I would actually view them as part of the joint itself, more than structural members in their own right). The posts and (more particularly) beams are still subject to substantial bending/flexural loads, whereas in a perfect, fully triangulated 'spaceframe' structure every member would be in pure tension or compression.

If we did spaceframe timber garages, we could really upset the OP's builder with the small sections of timber that would do the job!

[singlecoil]

MintSprint said:

singlecoil said:

...it's all about triangulation, or as much of it as is possible (and necessary).

Well, as much as necessary, certainly. A post-and-beam frame is never triangulated as much as possible.

I meant possible in the sense of it being a building, and people needing to move from room to room without negotiating diagonal timbers.

[MintSprint]

singlecoil said:

I meant possible in the sense of it being a building, and people needing to move from room to room without negotiating diagonal timbers.

Yes, but even on external frames with no openings (eg. down the side wall of a garage), where it would be perfectly possible to use a full diagonal brace, it's not usual to do so (and not necessary, with the sections of timber normally used).





OP: Apologies, we've derailed your thread a bit!

It doesn't go into structural design in any great depth (and I wouldn't recommend ATTAK Z's 'Timber Designer's Manual' as light bedtime reading...), but TRADA's 'Green Oak in Construction', available for free download here, is a nice, readable primer if you want to be a bit better informed on the subject.

[singlecoil]

MintSprint said:

singlecoil said:

I meant possible in the sense of it being a building, and people needing to move from room to room without negotiating diagonal timbers.

Yes, but even on external frames with no openings (eg. down the side wall of a garage), where it would be perfectly possible to use a full diagonal brace, it's not usual to do so (and not necessary, with the sections of timber normally used).

It would also be wasteful, timber does grow on trees, but that doesn't mean it's cheap.

[MintSprint]

singlecoil said:

It would also be wasteful, timber does grow on trees, but that doesn't mean it's cheap.

Absolutely.

But none the less, the structural approach is totally different to that of a fully triangulated structure.

A post-and-beam frame, as the name suggests, is fundamentally comprised of simply-supported horizontal beams, sitting on posts that transfer the loads from the beams vertically down to the foundations. The corner braces merely stiffen the post-beam connections sufficiently to allow the posts to stabilise the structure against racking. In so doing, they are actually introducing bending moments into the posts and beams, so that these main structural members are resisting the racking in bending.

Imagine if the corner braces were omitted, and instead you used steel right-angled flitch plates to do their job of stiffening the post-beam connections. You have essentially the same structural approach; you're just using the steel to concentrate the flexural stiffness of the joint into a slightly smaller area.

A fully triangulated structure (eg. a spaceframe or a truss), in comparison, could have pin-joined connections (ie. absolutely no flexural strength in the connection whatsoever - a free hinge, effectively) and would still be rigid, because the triangulation takes all the loads out through the members in pure tension or compression - no bending.




Corner braces triangulate the joint not the frame in other words.

[singlecoil]

MintSprint said:

singlecoil said:

It would also be wasteful, timber does grow on trees, but that doesn't mean it's cheap.

Absolutely.

But none the less, the structural approach is totally different to that of a fully triangulated structure.

A post-and-beam frame, as the name suggests, is fundamentally comprised of simply-supported horizontal beams, sitting on posts that transfer the loads from the beams vertically down to the foundations. The corner braces merely stiffen the post-beam connections sufficiently to allow the posts to stabilise the structure against racking. In so doing, they are actually introducing bending moments into the posts and beams, so that these main structural members are resisting the racking in bending.

Imagine if the corner braces were omitted, and instead you used steel right-angled flitch plates to do their job of stiffening the post-beam connections. You have essentially the same structural approach; you're just using the steel to concentrate the flexural stiffness of the joint into a slightly smaller area.

A fully triangulated structure (eg. a spaceframe or a truss), in comparison, could have pin-joined connections (ie. absolutely no flexural strength in the connection whatsoever - a free hinge, effectively) and would still be rigid, because the triangulation takes all the loads out through the members in pure tension or compression - no bending.




Corner braces triangulate the joint not the frame in other words.

Thanks for taking the trouble to write all that, I already knew it, but others might find it interesting.

[ATTAK Z]

MintSprint said:

singlecoil said:

It would also be wasteful, timber does grow on trees, but that doesn't mean it's cheap.

Absolutely.

But none the less, the structural approach is totally different to that of a fully triangulated structure.

A post-and-beam frame, as the name suggests, is fundamentally comprised of simply-supported horizontal beams, sitting on posts that transfer the loads from the beams vertically down to the foundations. The corner braces merely stiffen the post-beam connections sufficiently to allow the posts to stabilise the structure against racking. In so doing, they are actually introducing bending moments into the posts and beams, so that these main structural members are resisting the racking in bending.

Imagine if the corner braces were omitted, and instead you used steel right-angled flitch plates to do their job of stiffening the post-beam connections. You have essentially the same structural approach; you're just using the steel to concentrate the flexural stiffness of the joint into a slightly smaller area.

A fully triangulated structure (eg. a spaceframe or a truss), in comparison, could have pin-joined connections (ie. absolutely no flexural strength in the connection whatsoever - a free hinge, effectively) and would still be rigid, because the triangulation takes all the loads out through the members in pure tension or compression - no bending.




Corner braces triangulate the joint not the frame in other words.

I knew that !

[MintSprint]

singlecoil said:

Thanks for taking the trouble to write all that, I already knew it, but others might find it interesting.

Then you also know that it's not about reducing the size of the bracing to minimise obstructions for 'people needing to move from room to room without negotiating diagonal timbers', and it's not about providing as much bracing as possible its about asking the bracing to do a completely different job, and sizing it as necessary to do that job.

[ATTAK Z]

Just to add, timber bracing is more efficient when acting in compression as opposed to steel which usually is more efficient in tension ...




... I think

[anonymous-user]

Lots of good info from Mintsprint there.

The TRADA Green Oak frame book is a great starting point (even better 'cause its free) to understand a little more about post and beam construction methods.

Edited by anonymous-user on Friday 31st October 23:45

[singlecoil]

MintSprint said:

singlecoil said:

Thanks for taking the trouble to write all that, I already knew it, but others might find it interesting.

Then you also know that it's not about reducing the size of the bracing to minimise obstructions for 'people needing to move from room to room without negotiating diagonal timbers', and it's not about providing as much bracing as possible its about asking the bracing to do a completely different job, and sizing it as necessary to do that job.

You might be surprised at how much I know about oak framed buildings.

[MintSprint]

singlecoil said:

You might be surprised at how much I know about oak framed buildings.

Possibly.

I can only base my judgement on what you have said, of course, and what you said, suggested a limited knowledge of structural design (nothing to do with oak framed buildings, specifically). Or maybe it was just a poor and injudicious choice of language. Either way, I felt it would be helpful to other readers of the thread to expound.

You only have to look at the amount of distortion that has occurred in many of our older oak framed buildings to recognise that whilst the artisan craftsmen who created them had a lifetime's experience in oak framing, they knew diddley squat about structural analysis.

Edited by MintSprint on Saturday 1st November 08:33

[singlecoil]

MintSprint said:

singlecoil said:

You might be surprised at how much I know about oak framed buildings.

Possibly.

I can only base my judgement on what you have said, of course, and what you said[i], suggested a limited knowledge of [i]structural design (nothing to do with oak framed buildings, specifically). Or maybe it was just a poor and injudicious choice of language. Either way, I felt it would be helpful to other readers of the thread to expound.

You only have to look at the amount of distortion that has occurred in many of our older oak framed buildings to recognise that whilst the artisan craftsmen who created them had a lifetime's experience in oak framing, they knew diddley squat about structural analysis.

It's evident that you wish to be the sole owner of this subject on this forum. Fill your boots.