As per subject, is Birch any good as structural timber?

I've got a large birch that came down in a storm a few weeks ago
(waterlogged ground and it was on the edge of our woods) - I was going to
chop and dry it for firewood, but then it occured to me that I want to
put some more floors in our barn one day and I could get four hefty 8'
posts out of it (I'd likely just keep 'em as-is, bark and all).

That's assuming it's not going to rot or distort horribly if I try and
store it under cover for a few years, though...

cheers

Jules

Jules Richardson wrote:


As per subject, is Birch any good as structural timber?

In terms of strength and elasticity it's better than oak, downside is it has
no durability or resistance to wood borers. It makes good plywood if kept
dry and it also absorbs preservatives well.

I've got a large birch that came down in a storm a few weeks ago
(waterlogged ground and it was on the edge of our woods) - I was going to
chop and dry it for firewood,

Best thing for it


but then it occured to me that I want to
put some more floors in our barn one day and I could get four hefty 8'
posts out of it (I'd likely just keep 'em as-is, bark and all).

Birch bark is waterproof and it keeps the moisture in, hence it will rot
within the bark, rotting produces water so you end up with a bark enclosed
mush.

AJH

On Mon, 02 Aug 2010 21:35:17 +0100, andrew wrote:

Jules Richardson wrote:


As per subject, is Birch any good as structural timber?

In terms of strength and elasticity it's better than oak, downside is it
has no durability or resistance to wood borers. It makes good plywood if
kept dry and it also absorbs preservatives well.

Ta... I'll squirrel that info away in the back of my head :-) I'll have
to think if I know any tame sawmill folk who might be able to do
something with it for me.

I've got a large birch that came down in a storm a few weeks ago
(waterlogged ground and it was on the edge of our woods) - I was going
to chop and dry it for firewood,

Best thing for it

Fairy nuff. Probably back to seeing if the telegraph pole I have is any
good, then! Just seemed a shame to chop it as it's a big mature tree with
a nice straight trunk to it, but it sounds as though I'd have to at least
strip it and bombard it with chemicals first.

Question: is unseasoned timber as strong (or stronger) than seasoned
stuff? I do also have a need of some temporary supports / scaffold in the
barn while I'm doing various repair work, so maybe that tree would still
be useful there...

but then it occured to me that I want to put some more floors in our
barn one day and I could get four hefty 8' posts out of it (I'd likely
just keep 'em as-is, bark and all).

Birch bark is waterproof and it keeps the moisture in, hence it will rot
within the bark, rotting produces water so you end up with a bark
enclosed mush.

Yeah, I see that often - those trees come down a lot (but also grow fast
and pack themselves in quite densely) and many a time I've walked over a
downed one only for my foot to go straight through the bark.

cheers

Jules

"Jules Richardson" wrote in message
...

As per subject, is Birch any good as structural timber?

I've got a large birch that came down in a storm a few weeks ago
(waterlogged ground and it was on the edge of our woods) - I was going to
chop and dry it for firewood, but then it occured to me that I want to
put some more floors in our barn one day and I could get four hefty 8'
posts out of it (I'd likely just keep 'em as-is, bark and all).

That's assuming it's not going to rot or distort horribly if I try and
store it under cover for a few years, though...

cheers

Jules

No: but lots of other uses:

http://www.thewoodbox.com/data/wood/birchinfo.htm

http://www.google.co.uk/search?q=bir...ient=firefox-a

Makes interesting reading.

S

On 2 Aug, 22:53, Jules Richardson
wrote:
On Mon, 02 Aug 2010 21:35:17 +0100, andrew wrote:
Jules Richardson wrote:

As per subject, is Birch any good as structural timber?

In terms of strength and elasticity it's better than oak, downside is it
has no durability or resistance to wood borers. It makes good plywood if
kept dry and it also absorbs preservatives well.

Ta... I'll squirrel that info away in the back of my head :-) I'll have
to think if I know any tame sawmill folk who might be able to do
something with it for me.

I've got a large birch that came down in a storm a few weeks ago
(waterlogged ground and it was on the edge of our woods) - I was going
to chop and dry it for firewood,

Best thing for it

Fairy nuff. Probably back to seeing if the telegraph pole I have is any
good, then! Just seemed a shame to chop it as it's a big mature tree with
a nice straight trunk to it, but it sounds as though I'd have to at least
strip it and bombard it with chemicals first.

Question: is unseasoned timber as strong (or stronger) than seasoned
stuff? I do also have a need of some temporary supports / scaffold in the
barn while I'm doing various repair work, so maybe that tree would still
be useful there...

but then it occured to me that I want to put some more floors in our
barn one day and I could get four hefty 8' posts out of it (I'd likely
just keep 'em as-is, bark and all).

Birch bark is waterproof and it keeps the moisture in, hence it will rot
within the bark, rotting produces water so you end up with a bark
enclosed mush.

Yeah, I see that often - those trees come down a lot (but also grow fast
and pack themselves in quite densely) and many a time I've walked over a
downed one only for my foot to go straight through the bark.

cheers

Jules

Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as
it dries. I imagine this will be due to the cells no longer having
water in them. Certainly dry wood is far harder when turning -
turning wet wood produces wonderful great long shavings.

I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. I was interested in what the load capacity of 4 x 4 pine was
- and it far exceeded my load of a bit less than 1000kg.

You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.

Rob

On Mon, 02 Aug 2010 15:36:42 -0700, robgraham wrote:
Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as it
dries. I imagine this will be due to the cells no longer having water
in them. Certainly dry wood is far harder when turning - turning wet
wood produces wonderful great long shavings.

I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. I was interested in what the load capacity of 4 x 4 pine was -
and it far exceeded my load of a bit less than 1000kg.

You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.

Thanks for that! I suppose another way of looking at it is that any given
section of trunk is supporting the weight of the rest of the tree above
it - so under compression, when wet, any lower sections of trunk have
quite a significant weight upon them.

My gut feeling is that I could put a huge load on four 8' long sections
of 'wet' trunk - but as I'd want to be working on top of it all, it'd be
nice to run a few numbers :-)

cheers

Jules

Jules Richardson wrote:
On Mon, 02 Aug 2010 15:36:42 -0700, robgraham wrote:
Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as it
dries. I imagine this will be due to the cells no longer having water
in them. Certainly dry wood is far harder when turning - turning wet
wood produces wonderful great long shavings.

I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. I was interested in what the load capacity of 4 x 4 pine was -
and it far exceeded my load of a bit less than 1000kg.

You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.

Thanks for that! I suppose another way of looking at it is that any given
section of trunk is supporting the weight of the rest of the tree above
it - so under compression, when wet, any lower sections of trunk have
quite a significant weight upon them.

My gut feeling is that I could put a huge load on four 8' long sections
of 'wet' trunk - but as I'd want to be working on top of it all, it'd be
nice to run a few numbers :-)

We are talking tons here Jules.
For any reasonable length of pole, the dominant failure mode is not
compressive strength, but tensile strength combineed with elasticity.
Google Euler's slender column theory - essentially if the rate of change
or resistive elsatic force for a delta bowing is negative, you go into
full bowing and collapse. The dominant bowing eigen(value/Vector) [cant
remember]..is the 'first harmonic - i.e. the simple bow.

wood becomes stiffer as it dries, so that improves slender column max
weight.

Compressive strength is more or less unaffected.

Depending on how thick those 8' sections are, you will probably (waves
wet finger) start to see Euler instability down around 4 " diameter.

And that can be prevented by trussing the stricture with cross braces.

Certainly 8x3 timber is great as vertical studwork, but needs trussing
in the thin direction.

Birch is not the greatest structural timber in the world., Its lighter
and less strong than typical structural lumber, but its not bad either.
Good for plywood anyway. Outside it rots fast..many species of fungi
love birch.




cheers

Jules

On 3 Aug, 16:38, The Natural Philosopher wrote:
Jules Richardson wrote:
On Mon, 02 Aug 2010 15:36:42 -0700, robgraham wrote:
Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as it
dries. *I imagine this will be due to the cells no longer having water
in them. *Certainly dry wood is far harder when turning - turning wet
wood produces wonderful great long shavings.

I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. *I was interested in what the load capacity of 4 x 4 pine was -
and it far exceeded my load of a bit less than 1000kg.

You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.

Thanks for that! I suppose another way of looking at it is that any given
section of trunk is supporting the weight of the rest of the tree above
it - so under compression, when wet, any lower sections of trunk have
quite a significant weight upon them.

My gut feeling is that I could put a huge load on four 8' long sections
of 'wet' trunk - but as I'd want to be working on top of it all, it'd be
nice to run a few numbers :-)

We are talking tons here Jules.
For any reasonable length of pole, the dominant failure mode is not
compressive strength, but tensile strength combineed with elasticity.
Google Euler's slender column theory - essentially if the rate of change
or resistive elsatic force for a delta bowing is negative, you go into
full bowing and collapse. The dominant bowing eigen(value/Vector) [cant
remember]..is the 'first harmonic - i.e. the simple bow.

wood becomes stiffer as it dries, so that improves slender column max
weight.

Compressive strength is more or less unaffected.

Depending on how thick those 8' sections are, you will probably (waves
wet finger) start to see Euler instability down around 4 " diameter.

And that can be prevented by trussing the stricture with cross braces.

Certainly 8x3 timber is great as vertical studwork, but needs trussing
in the thin direction.

Birch is not the greatest structural timber in the world., Its lighter
and less strong than typical structural lumber, but its not bad either.
Good for plywood anyway. Outside it rots fast..many species of fungi
love birch.



cheers

Jules

Hmm - it looks as if I have some more reading to do ! Thanks for that
input, NP - I'm looking at the design for a self build conservatory
and have some 4 x 4s I'm looking at using.

I take it that the failure mode is that the column starts to bow
rather than crush so the force becomes tensile rather than
compressive ?

I'm electronics rather than mechanics so I may put this one back to my
mechanical friend who no doubt hasn't used it since university days 40
years ago !

Rob

Rob

robgraham wrote:
On 3 Aug, 16:38, The Natural Philosopher wrote:
Jules Richardson wrote:
On Mon, 02 Aug 2010 15:36:42 -0700, robgraham wrote:
Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as it
dries. I imagine this will be due to the cells no longer having water
in them. Certainly dry wood is far harder when turning - turning wet
wood produces wonderful great long shavings.
I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. I was interested in what the load capacity of 4 x 4 pine was -
and it far exceeded my load of a bit less than 1000kg.
You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.
Thanks for that! I suppose another way of looking at it is that any given
section of trunk is supporting the weight of the rest of the tree above
it - so under compression, when wet, any lower sections of trunk have
quite a significant weight upon them.
My gut feeling is that I could put a huge load on four 8' long sections
of 'wet' trunk - but as I'd want to be working on top of it all, it'd be
nice to run a few numbers :-)
We are talking tons here Jules.
For any reasonable length of pole, the dominant failure mode is not
compressive strength, but tensile strength combineed with elasticity.
Google Euler's slender column theory - essentially if the rate of change
or resistive elsatic force for a delta bowing is negative, you go into
full bowing and collapse. The dominant bowing eigen(value/Vector) [cant
remember]..is the 'first harmonic - i.e. the simple bow.

wood becomes stiffer as it dries, so that improves slender column max
weight.

Compressive strength is more or less unaffected.

Depending on how thick those 8' sections are, you will probably (waves
wet finger) start to see Euler instability down around 4 " diameter.

And that can be prevented by trussing the stricture with cross braces.

Certainly 8x3 timber is great as vertical studwork, but needs trussing
in the thin direction.

Birch is not the greatest structural timber in the world., Its lighter
and less strong than typical structural lumber, but its not bad either.
Good for plywood anyway. Outside it rots fast..many species of fungi
love birch.



cheers
Jules

Hmm - it looks as if I have some more reading to do ! Thanks for that
input, NP - I'm looking at the design for a self build conservatory
and have some 4 x 4s I'm looking at using.

4x4 birch? VERY nice indoors. I like birch. Not outside please, not
without treatment.

I take it that the failure mode is that the column starts to bow
rather than crush so the force becomes tensile rather than
compressive ?


Yup. EASILY fixed by bracing.

In fairness a bending force is compressive on one side and tensile on
the other, but wood usually gives by tensile first. Concrete certainly
does, which is why we pre-stress it. The idea being the concrete never
is being pulled apart under any load..the steel takes all the tensile
forces. You can do that with a steel cable inside a wood beam as well.


I'm electronics rather than mechanics so I may put this one back to my
mechanical friend who no doubt hasn't used it since university days 40
years ago !

Once I did the maths, Now I remember the principle, and use the tables.
that most places have. Or consult a specialist.

Any architect certainly will. Any form of structural engineers will
advise for a couple of hundred as well.

The best source for wood tables at the raw structural level is
'understanding wood' by Hoadley. THE definitive tome and worth every
penny. It's a great read if you are interested on wood anyway. Highly
recommended.


Rob

Rob

On 3 Aug, 17:36, robgraham wrote:
On 3 Aug, 16:38, The Natural Philosopher wrote:





Jules Richardson wrote:
On Mon, 02 Aug 2010 15:36:42 -0700, robgraham wrote:
Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as it
dries. *I imagine this will be due to the cells no longer having water
in them. *Certainly dry wood is far harder when turning - turning wet
wood produces wonderful great long shavings.

I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. *I was interested in what the load capacity of 4 x 4 pine was -
and it far exceeded my load of a bit less than 1000kg.

You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.

Thanks for that! I suppose another way of looking at it is that any given
section of trunk is supporting the weight of the rest of the tree above
it - so under compression, when wet, any lower sections of trunk have
quite a significant weight upon them.

My gut feeling is that I could put a huge load on four 8' long sections
of 'wet' trunk - but as I'd want to be working on top of it all, it'd be
nice to run a few numbers :-)

We are talking tons here Jules.
For any reasonable length of pole, the dominant failure mode is not
compressive strength, but tensile strength combineed with elasticity.
Google Euler's slender column theory - essentially if the rate of change
or resistive elsatic force for a delta bowing is negative, you go into
full bowing and collapse. The dominant bowing eigen(value/Vector) [cant
remember]..is the 'first harmonic - i.e. the simple bow.

wood becomes stiffer as it dries, so that improves slender column max
weight.

Compressive strength is more or less unaffected.

Depending on how thick those 8' sections are, you will probably (waves
wet finger) start to see Euler instability down around 4 " diameter.

And that can be prevented by trussing the stricture with cross braces.

Certainly 8x3 timber is great as vertical studwork, but needs trussing
in the thin direction.

Birch is not the greatest structural timber in the world., Its lighter
and less strong than typical structural lumber, but its not bad either.
Good for plywood anyway. Outside it rots fast..many species of fungi
love birch.

cheers

Jules

Hmm - it looks as if I have some more reading to do ! *Thanks for that
input, NP - I'm looking at the design for a self build conservatory
and have some 4 x 4s I'm looking at using.

I take it that the failure mode is that the column starts to bow
rather than crush so the force becomes tensile rather than
compressive ?

I'm electronics rather than mechanics so I may put this one back to my
mechanical friend who no doubt hasn't used it since university days 40
years ago !

Rob

Rob

My mechanical friend was not impressed about being asked questions on
a topic which he didn't really understand over 40 years ago !

Anyway I found this

"For a column of length L and cross section radius of gyration rho, it
is possible to distinguish 3 failure regimes under compression:

Long column range: for large values of L/rho (usually above 60) the
failure is elastic and Euler’s equation is valid.
Short column range: for intermediate values of L/rho (usually between
20 and 60) the failure is inelastic and Euler’s equation is no longer
valid. Several semi-empirical methods have been developed to describe
failure in this region from the engineering point of view, e.g.
Johnson’s equation. The book “Analysis and Design of Flight Vehicle
Structures” by E. F. Bruhn has a good compendium of methods and design
tables.
Block compression range: for small values of L/rho (usually under 20)
the failure is completely plastic and can be assumed to be, in absence
of cross sectional instabilities, equal to the compressive yield
strength of the material."

Having had to google for 'radius if gyration' and then '2nd moment of
inertia', I find my column is an intermediate one, but as the load is
less than 20% of the recommended maximum working compressive stress
I'm comfortable that I don't have a problem, but will include this
data in the design record.

I do think somehow, Jules, that are going into this a little deeper
than you had intended ! :)

Rob

robgraham wrote:
On 3 Aug, 17:36, robgraham wrote:
On 3 Aug, 16:38, The Natural Philosopher wrote:





Jules Richardson wrote:
On Mon, 02 Aug 2010 15:36:42 -0700, robgraham wrote:
Jules - if you google on timber compressive strength you will find all
sorts of hits but the outcome seems to be that wood gets stronger as it
dries. I imagine this will be due to the cells no longer having water
in them. Certainly dry wood is far harder when turning - turning wet
wood produces wonderful great long shavings.
I couldn't get the compressive strength for different timbers but a
maximum working figure I got for ship builders using douglas fir is
1100psi which as everything else I was working with was SI units is 70
kg/cm^2. I was interested in what the load capacity of 4 x 4 pine was -
and it far exceeded my load of a bit less than 1000kg.
You might find a derating somewhere for wet wood, but it could be that
you have a sufficient safety margin from those figures.
Thanks for that! I suppose another way of looking at it is that any given
section of trunk is supporting the weight of the rest of the tree above
it - so under compression, when wet, any lower sections of trunk have
quite a significant weight upon them.
My gut feeling is that I could put a huge load on four 8' long sections
of 'wet' trunk - but as I'd want to be working on top of it all, it'd be
nice to run a few numbers :-)
We are talking tons here Jules.
For any reasonable length of pole, the dominant failure mode is not
compressive strength, but tensile strength combineed with elasticity.
Google Euler's slender column theory - essentially if the rate of change
or resistive elsatic force for a delta bowing is negative, you go into
full bowing and collapse. The dominant bowing eigen(value/Vector) [cant
remember]..is the 'first harmonic - i.e. the simple bow.
wood becomes stiffer as it dries, so that improves slender column max
weight.
Compressive strength is more or less unaffected.
Depending on how thick those 8' sections are, you will probably (waves
wet finger) start to see Euler instability down around 4 " diameter.
And that can be prevented by trussing the stricture with cross braces.
Certainly 8x3 timber is great as vertical studwork, but needs trussing
in the thin direction.
Birch is not the greatest structural timber in the world., Its lighter
and less strong than typical structural lumber, but its not bad either.
Good for plywood anyway. Outside it rots fast..many species of fungi
love birch.
cheers
Jules
Hmm - it looks as if I have some more reading to do ! Thanks for that
input, NP - I'm looking at the design for a self build conservatory
and have some 4 x 4s I'm looking at using.

I take it that the failure mode is that the column starts to bow
rather than crush so the force becomes tensile rather than
compressive ?

I'm electronics rather than mechanics so I may put this one back to my
mechanical friend who no doubt hasn't used it since university days 40
years ago !

Rob

Rob

My mechanical friend was not impressed about being asked questions on
a topic which he didn't really understand over 40 years ago !

Anyway I found this

"For a column of length L and cross section radius of gyration rho, it
is possible to distinguish 3 failure regimes under compression:

Long column range: for large values of L/rho (usually above 60) the
failure is elastic and Eulers equation is valid.
Short column range: for intermediate values of L/rho (usually between
20 and 60) the failure is inelastic and Eulers equation is no longer
valid. Several semi-empirical methods have been developed to describe
failure in this region from the engineering point of view, e.g.
Johnsons equation. The book €œAnalysis and Design of Flight Vehicle
Structures€� by E. F. Bruhn has a good compendium of methods and design
tables.
Block compression range: for small values of L/rho (usually under 20)
the failure is completely plastic and can be assumed to be, in absence
of cross sectional instabilities, equal to the compressive yield
strength of the material."

Having had to google for 'radius if gyration' and then '2nd moment of
inertia', I find my column is an intermediate one, but as the load is
less than 20% of the recommended maximum working compressive stress
I'm comfortable that I don't have a problem, but will include this
data in the design record.

I do think somehow, Jules, that are going into this a little deeper
than you had intended ! :)

Rob

I raise my hat to you. I even vaguely remember what radius of gyration
and second moment of inertia are..

But the intermediate mode is interesting. I gave this **** up faster
than you could whisper 'semiconductor' and followed your route..

But my gut feel that you were on the slender side of complete stability
seems borne out.

AS usual watching struts creaking and moving sideways and yelling
'whoa--it needs a bit o' bracing mate' is just as valuable as the
calculus. :-)

On Tue, 03 Aug 2010 10:24:04 -0700, robgraham wrote:
I do think somehow, Jules, that are going into this a little deeper than
you had intended ! :)

Heh :-) Not a problem... I've not properly digested it yet, but it's good
stuff to learn.

Oh, I just measured the trunk in question - four 8' lengths gives me a
minimum diameter of 7", which is roughly equivalent to a 6"x6" post,
assuming things can be directly translated like that.

cheers

Jules

Jules Richardson wrote:
On Tue, 03 Aug 2010 10:24:04 -0700, robgraham wrote:
I do think somehow, Jules, that are going into this a little deeper than
you had intended ! :)

Heh :-) Not a problem... I've not properly digested it yet, but it's good
stuff to learn.

Oh, I just measured the trunk in question - four 8' lengths gives me a
minimum diameter of 7", which is roughly equivalent to a 6"x6" post,
assuming things can be directly translated like that.

Pretty much stable at that sort of size.

You will get failure around wherever the load is being transferred. Not
from the logs themselves.


The gut feel of 'log' versus 'pole' is about where you transition from
other failure modes to Euler instability.


cheers

Jules