Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat hand-wavy...

I'm going to need to jack up parts of our old timber-framed barn as I work
on the end wall*, and being able to estimate the size of floor jacks
needed would be useful (and I'll add on a wide safety margin, of course).

* for some very strange reason they ran poured concrete round three
walls (up to about 3' high), but only did half of the fourth. Of course 60
years of moisture hasn't been kind to the 'missing' section where the wood
extends down as far as ground level - the framework's gradually rotted
from the ground up, dropping about 3" in the process along that section.
Thankfully it's an end wall, not side, so doesn't have all of the roof
weight on it...

It's a bit of a longer-term project, but figured I'd ask and then I could
keep an eye out for the necessary jacks in the meantime.

cheers

Jules

"Jules" wrote in message
news

Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat hand-wavy...

I'm going to need to jack up parts of our old timber-framed barn as I work
on the end wall*, and being able to estimate the size of floor jacks
needed would be useful (and I'll add on a wide safety margin, of course).

* for some very strange reason they ran poured concrete round three
walls (up to about 3' high), but only did half of the fourth. Of course 60
years of moisture hasn't been kind to the 'missing' section where the wood
extends down as far as ground level - the framework's gradually rotted
from the ground up, dropping about 3" in the process along that section.
Thankfully it's an end wall, not side, so doesn't have all of the roof
weight on it...

It's a bit of a longer-term project, but figured I'd ask and then I could
keep an eye out for the necessary jacks in the meantime.

http://www.ttf.co.uk/Directory/Detai...b-92d0257f83e9

"Jules" wrote in message
news

Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat hand-wavy...

I'm going to need to jack up parts of our old timber-framed barn as I work
on the end wall*, and being able to estimate the size of floor jacks
needed would be useful (and I'll add on a wide safety margin, of course).

* for some very strange reason they ran poured concrete round three
walls (up to about 3' high), but only did half of the fourth. Of course 60
years of moisture hasn't been kind to the 'missing' section where the wood
extends down as far as ground level - the framework's gradually rotted
from the ground up, dropping about 3" in the process along that section.
Thankfully it's an end wall, not side, so doesn't have all of the roof
weight on it...

It's a bit of a longer-term project, but figured I'd ask and then I could
keep an eye out for the necessary jacks in the meantime.


Sounds like you need the services of qualified structural engineer to advise
you.

Peter Crosland

On Mon, 24 Aug 2009 20:46:20 +0100, Peter Crosland wrote:
Sounds like you need the services of qualified structural engineer to advise
you.

Quite possibly - although what would they do (purely out of curiosity)?
Would they cook up some 3D model of the structure, take samples of
materials and weigh, and work it out from that? I'm intrigued by what the
exact process would be... (mainly because I'm surprised anyone can give an
exact answer without a truly enormous - and perhaps impractical - amount
of work, although I'm sure a reasonable estimate based on a few
calculations and a lot of experience could be attaioned)

cheers!

J.

"Jules" wrote in message
news
On Mon, 24 Aug 2009 20:46:20 +0100, Peter Crosland wrote:
Sounds like you need the services of qualified structural engineer to
advise
you.

Quite possibly - although what would they do (purely out of curiosity)?
Would they cook up some 3D model of the structure, take samples of
materials and weigh, and work it out from that? I'm intrigued by what the
exact process would be... (mainly because I'm surprised anyone can give an
exact answer without a truly enormous - and perhaps impractical - amount
of work, although I'm sure a reasonable estimate based on a few
calculations and a lot of experience could be attaioned)


The problem is that there are a lot of variables to consider and the job is
not all calculation. I only suggest it because of the potential for disaster
if you try and DIY it.

Peter Crosland

Peter Crosland wrote:
"Jules" wrote in message
news
On Mon, 24 Aug 2009 20:46:20 +0100, Peter Crosland wrote:
Sounds like you need the services of qualified structural engineer to
advise
you.
Quite possibly - although what would they do (purely out of curiosity)?
Would they cook up some 3D model of the structure, take samples of
materials and weigh, and work it out from that? I'm intrigued by what the
exact process would be... (mainly because I'm surprised anyone can give an
exact answer without a truly enormous - and perhaps impractical - amount
of work, although I'm sure a reasonable estimate based on a few
calculations and a lot of experience could be attaioned)


The problem is that there are a lot of variables to consider and the job is
not all calculation. I only suggest it because of the potential for disaster
if you try and DIY it.

Peter Crosland


Ive seen substantial stuff jacked up on Acrow props.

The rule seems to be 'if you cant get enough force on the Acrow to jack
it, its too heavy'

I do remember the 6x4 beam across an old shed we used to put a 5 tonne
yacht pulley and hoist on to lift a Morris 1500 engine out..only when
the 5 tonne pulley bent, and the beam deflected about 6 inches, did we
realise that the whole front of the car was 3 " off the deck.. 'er I
think the engine has caught on something chaps'

The Natural Philosopher wrote:

I do remember the 6x4 beam across an old shed we used to put a 5 tonne
yacht pulley and hoist on to lift a Morris 1500 engine out..only when
the 5 tonne pulley bent, and the beam deflected about 6 inches, did we
realise that the whole front of the car was 3 " off the deck.. 'er I
think the engine has caught on something chaps'

Weigh more than 5 tons, that Morris, did it?

Si

On Mon, 24 Aug 2009 16:10:37 -0500, Jules wrote:
On Mon, 24 Aug 2009 20:46:20 +0100, Peter Crosland wrote:
Sounds like you need the services of qualified structural engineer to advise
you.

Quite possibly - although what would they do (purely out of curiosity)?
Would they cook up some 3D model of the structure, take samples of
materials and weigh, and work it out from that? I'm intrigued by what the
exact process would be... (mainly because I'm surprised anyone can give an
exact answer without a truly enormous - and perhaps impractical - amount
of work, although I'm sure a reasonable estimate based on a few
calculations and a lot of experience could be attaioned)

Well, you don't need a precise answer - what you need is a "not less than X"
answer and then to get provision to support "X" (taking into account how
the load is distributed, how to go about raising / supporting it without
adding undue stresses) and all the elfin malarkey, too. I'd suggest that the
calculations are quite a small part of the issue. What you'd be paying for
is the experience of the S/E to know how to go about the job.
Plus of course, having someone to sue if it all goes wrong :-)

On Tue, 25 Aug 2009 08:53:26 +0000, pete wrote:

On Mon, 24 Aug 2009 16:10:37 -0500, Jules wrote:
On Mon, 24 Aug 2009 20:46:20 +0100, Peter Crosland wrote:
Sounds like you need the services of qualified structural engineer to advise
you.

Quite possibly - although what would they do (purely out of curiosity)?
Would they cook up some 3D model of the structure, take samples of
materials and weigh, and work it out from that? I'm intrigued by what the
exact process would be... (mainly because I'm surprised anyone can give an
exact answer without a truly enormous - and perhaps impractical - amount
of work, although I'm sure a reasonable estimate based on a few
calculations and a lot of experience could be attaioned)

Well, you don't need a precise answer - what you need is a "not less than X"

Indeed.

answer and then to get provision to support "X" (taking into account how
the load is distributed, how to go about raising / supporting it without
adding undue stresses) and all the elfin malarkey, too.

Thankfully no elfin ******** where I am, but yes, I do need to worry
about exactly where to jack / support. Currently the weight for the
damaged section is distributed between the wall's framework (which has
rotted at the bottom, but still appears to be resting "solidly" on the
ground) and on one of the primary beams which runs the length of the
barn.

I suspect I'll end up supporting that beam (just to be on the safe
side) then jacking it as close to the end wall as I can*. I'm actually
tempted to use a 3 ton truck jack, purely because I can then run the
handle through a hole in the wall (the cladding will all be replaced
anyway) and jack it from outside. Being right next to a floor jack whilst
jacking it up makes me a little jittery :-)

* it's a 6x6" beam made from three 6x2" boards - but whoever made it
put the overlaps all within a couple of feet of each other. It's bent
around this point as the wall's sunk, and remains to be seen whether
it'll bend back the other way when things are jacked up.

For a wooden structure that's 60 years old, with little weather
protection, and which has apparently seen very little maintenance during
its life, I suppose it's amazing that it's still standing at all. The fact
that it's such a wreck make it more of an interesting DIY project, though!
:-)

cheers

Jules

On 24 Aug, 19:39, Jules
wrote:
Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat hand-wavy...

Greenheart 10
Oak 8
Iroko, Teak 7
Mahogany 6

kN/m3, from the structural engineer's pocket book p34

Jules wrote:
Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat hand-wavy...

I'm going to need to jack up parts of our old timber-framed barn as I work
on the end wall*, and being able to estimate the size of floor jacks
needed would be useful (and I'll add on a wide safety margin, of course).

* for some very strange reason they ran poured concrete round three
walls (up to about 3' high), but only did half of the fourth. Of course 60
years of moisture hasn't been kind to the 'missing' section where the wood
extends down as far as ground level - the framework's gradually rotted
from the ground up, dropping about 3" in the process along that section.
Thankfully it's an end wall, not side, so doesn't have all of the roof
weight on it...

It's a bit of a longer-term project, but figured I'd ask and then I could
keep an eye out for the necessary jacks in the meantime.


You need 'understanding wood' by Hoadley..


US book, and the very best there is.

However if you use a 'same density as water, i.e. a cubic meter weighs a
tonne' you will be slightly out on the safe side.

I.e. a block of oak floats..just. A block of lignum vitae sinks, but who
uses it?

a block of softwood like pine, probably floats half out of the water, so
is half the weight of the water.

If in doubt, cut a piece off and float it, and measure the waterline..


cheers

Jules

In an earlier contribution to this discussion,
Jules wrote:

Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat
hand-wavy...

Google is your friend! Typing "specific gravity of wood" into the search box
gives lots of hits, including this one:
http://www.simetric.co.uk/si_wood.htm

Since most wood floats in water, if you assume it has an SG of 1 (1 Tonne
per M^3) you will build in a reasonable safety margin.
--
Cheers,
Roger
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On Mon, 24 Aug 2009 21:38:46 +0100, Roger Mills wrote:

In an earlier contribution to this discussion,
Jules wrote:

Are there tables anywhere for the dry weights of timber of different
species by volume? I realise it's all likely to be somewhat
hand-wavy...

Google is your friend!

That relies on me bothering to use it I didn't realise it'd be that
easy - I figured it'd be one of those things that was either buried in a
textbook or within the heads of more clueful folk...

Since most wood floats in water, if you assume it has an SG of 1 (1
Tonne per M^3) you will build in a reasonable safety margin.

That works. Initial estimate then, and given that the roof structure
transmits most of its load to other walls, I think that 3 tonnes is
probably a reasonable number - but I'll do some exact measurements and
take it from there! (it's high enough that I think that 2-tonne jacks
might be pushing it a little, at any rate)

cheers

Jules