wood tensile strength

I would definitely avoid putting wood in tension.
I've made clamps that put the stuff in tension that easily pulled
themselves apart.
X-dowels, bolts, and screws can also pull the fibers away from each
other.
Much easier and far more positive to use mending plates, dovetails (tho
clearly in tension), corner braces etc.; stuff that exploits the
material's best modes of strength.
http://www.patwarner.com (Routers)

I would definitely avoid putting wood in tension.
I've made clamps that put the stuff in tension that easily pulled
themselves apart.
X-dowels, bolts, and screws can also pull the fibers away from each
other.
Much easier and far more positive to use mending plates, dovetails (tho
clearly in tension), corner braces etc.; stuff that exploits the
material's best modes of strength.
http://www.patwarner.com (Routers)

"Chris Carruth" <[email protected]> wrote in message
news:[email protected]...
> Does anyone have formulas for calculating wood strength?
There is no formula for calculation the tensile strength of any material.
You find values in a book somewhere.
In addition, it is very ill advised to let the load become so high that the
internal stress approaches the tensile strength.

You also must consider the buckling load for columns.
Jim

"Chris Carruth" <[email protected]> wrote in message
news:[email protected]...
> Does anyone have formulas for calculating wood strength?
>
> I am making a table lift, consisting of three pieces of wood/steel, first
> piece with bushing t in the middle of it, position toward one end of a
long
> threaded rod. Second piece, with threaded nut wielded/epoxied, etc sits
only
> 2" above third piece. Third piece has casters. Seond and third piece will
> stay in line using two rods vertically between the pieces. Three pieces
> extend across table width on the inside of the table. Point is no wheels
> seen, mobility when necessary, and no casters when doing actual work.
>
> Goal is to turn threaded rod, which extends from above first piece,
through
> second, and then simply sits in a bushing drilled in the third piece.
> Turning rod raises or lowers third cross piece, which has the casters, due
> to presence of nut on second piece.
>
> Question is whether a hardwood, like OAK, would support the weight (500
lbs
> or so) or do I need to fashion a metal solution. There would be one of
these
> 3-piece lifts at each end of the table, meaning each would need to support
> 240-300 lbs of weight.
>
> Hope this is clear enough for an answer...thanks...

Your table weighs 500 pounds?
Wood can handle it probably, but it depends on how much wood and how the
load is applied.
My house is made of wood and it is strong. A toothpick is made of wood too.
You don't give nearly enough information to get a reasonable answer.
Try it out. Wood is cheap.

-j

Chris Carruth wrote:

> Does anyone have formulas for calculating wood strength?

They're the same as the formulas for calculating the strength of metal,
plastic, or any other material, at least to an engineering approximation.


> I am making a table lift, consisting of three pieces of wood/steel, first
> piece with bushing t in the middle of it, position toward one end of a
> long threaded rod. Second piece, with threaded nut wielded/epoxied, etc
> sits only 2" above third piece. Third piece has casters. Seond and third
> piece will stay in line using two rods vertically between the pieces.
> Three pieces extend across table width on the inside of the table. Point
> is no wheels seen, mobility when necessary, and no casters when doing
> actual work.
>
> Goal is to turn threaded rod, which extends from above first piece,
> through second, and then simply sits in a bushing drilled in the third
> piece. Turning rod raises or lowers third cross piece, which has the
> casters, due to presence of nut on second piece.
>
> Question is whether a hardwood, like OAK, would support the weight (500
> lbs or so) or do I need to fashion a metal solution. There would be one of
> these 3-piece lifts at each end of the table, meaning each would need to
> support 240-300 lbs of weight.

The USS Constitution is built mainly of OAK, and can support the weight of
on the order of 100,000 pounds of crew, plus supplies, cannons, wind loads,
sea loads, combat damage, etc up to a total displacement of around 2000
tons. So, yes, OAK, properly configured, can support 500 pounds.

The problem is how to configure it to do that.

> Hope this is clear enough for an answer...thanks...

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

[email protected] wrote:

> I would definitely avoid putting wood in tension.
> I've made clamps that put the stuff in tension that easily pulled
> themselves apart.
> X-dowels, bolts, and screws can also pull the fibers away from each
> other.
> Much easier and far more positive to use mending plates, dovetails (tho
> clearly in tension), corner braces etc.; stuff that exploits the
> material's best modes of strength.
> http://www.patwarner.com (Routers)

Well, now, every time a Mosquito with a full bomb load made a maximum
performance turn it put quite a lot of wood in quite a lot tension with no
difficulties at all. The USS Constitution any time she was running before
a good wind did the same (backstays were a new innovation that came along
after she was designed).

If you're applying a tensile load perpendicular to the grain then no, it's
not very strong--neither is graphite reinforced epoxy or any other
"oriented" material. The solution to that is to design so that tensile
loads are parallel to the grain, not perpendicular.



--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

In article <[email protected]>,
"Chris Carruth" <[email protected]> wrote:

> Does anyone have formulas for calculating wood strength?

I'm not sure if it'll solve your problem, but take a look at
http://www.woodweb.com/knowledge_base/Wood_Handbook.html

Chris Carruth" <[email protected]> wrote in message
news:[email protected]...
> Does anyone have formulas for calculating wood strength?
>
> I am making a table lift, consisting of three pieces of wood/steel, first
> piece with bushing t in the middle of it, position toward one end of a
long
> threaded rod. Second piece, with threaded nut wielded/epoxied, etc sits
only
> 2" above third piece. Third piece has casters. Seond and third piece will
> stay in line using two rods vertically between the pieces. Three pieces
> extend across table width on the inside of the table. Point is no wheels
> seen, mobility when necessary, and no casters when doing actual work.
>
> Goal is to turn threaded rod, which extends from above first piece,
through
> second, and then simply sits in a bushing drilled in the third piece.
> Turning rod raises or lowers third cross piece, which has the casters, due
> to presence of nut on second piece.
>
> Question is whether a hardwood, like OAK, would support the weight (500
lbs
> or so) or do I need to fashion a metal solution. There would be one of
these
> 3-piece lifts at each end of the table, meaning each would need to support
> 240-300 lbs of weight.
>
> Hope this is clear enough for an answer...thanks...

Well, it isn't nearly enough for an answer, but I'll give you some things to
think about. First, if you're supporting a table top that sounds like will
have something like 500-600 lbs sitting on it, my first guess is that your
wood pieces are mostly going to be loaded in compression, not tension. If
that's the case, depending on the design of the individual members, you
might have to worry more about buckling than compressive failure. For wood,
anything with a slendeness ratio of more than about 11 and you are likely to
have buckling as a primary mode of failure. But unless you know how to
calculate effective length of a column and radii of gyration, this is
definitely a case where a test will be more informative than attempting to
work out the calculations (just in case you didn't take four years of
engineering mechanics and strength of materials). Even for those of us that
did, it gets hard to remember. Consider that a piece of oak with a
cross-sectional area of 1 in^2 has a compressive strength of approximately
6000 lbs (and a tensile strength of approximately twice that), and I think
it's very unlikely that you are going to have a problem strength-wise in
strict tension or compression with a decent design.

todd

todd

<[email protected]> wrote in message
news:[email protected]...
> I would definitely avoid putting wood in tension.
> I've made clamps that put the stuff in tension that easily pulled
> themselves apart.
> X-dowels, bolts, and screws can also pull the fibers away from each
> other.
> Much easier and far more positive to use mending plates, dovetails (tho
> clearly in tension), corner braces etc.; stuff that exploits the
> material's best modes of strength.
> http://www.patwarner.com (Routers)
>

Wood is put in tension every day all over the world. Every single floor
joist and roof rafter is in both tension and in compression. The top is in
compression and the bottom is in tension.
--

-Mike-
[email protected]