nav
thanks--got it.
its been awhile but yes all that is understood
i can make the calculations, figure the loads, determine the max moment,
check the deflection, shear at the bolts etc.
all i need is the moment of interia and the section modulus (it is the
correct term) for an oval section
i don't generally deal with oval sections and none are listed in any manuals
i have here.
probably just need to search an alum. association reference. as i have alla
the dimensions of the section involved ( both axis, wall thickness)

i am looking for the section properties to understand max loading in a given
situation..
(working backwards)

as in S sub x (required) = M/f(alum.)
S sub x (actual) of a section = ??

whe
I = moment of interia (inches 4th)
S sub x = section modulus (inches 3rd)
M = moment (#-inches)
F sub b = bending stress. (psi)

simple statics really--i'll just pull a couple of books off the shelf and
dust em off.
actually i'll just call one of my engineers in the morning.
in the meantime.........i'm outta here to find a glass of wine and a blonde
thanks
gf.







"Nav" wrote in message
...


gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

You can use a simple rule of thumb. If you know the moment of intertia
for a box section of the same wall thickness and outside dimensions the
moment of inertial of the tube or ellipse that has the same dimension is
about 14% less.

Hope this gives you what you want.

Cheers

as the tune
gonefishiing wrote:
nav
thanks--got it.
its been awhile but yes all that is understood
i can make the calculations, figure the loads, determine the max moment,
check the deflection, shear at the bolts etc.
all i need is the moment of interia and the section modulus (it is the
correct term) for an oval section
i don't generally deal with oval sections and none are listed in any manuals
i have here.
probably just need to search an alum. association reference. as i have alla
the dimensions of the section involved ( both axis, wall thickness)

i am looking for the section properties to understand max loading in a given
situation..
(working backwards)

as in S sub x (required) = M/f(alum.)
S sub x (actual) of a section = ??

whe
I = moment of interia (inches 4th)
S sub x = section modulus (inches 3rd)
M = moment (#-inches)
F sub b = bending stress. (psi)

simple statics really--i'll just pull a couple of books off the shelf and
dust em off.
actually i'll just call one of my engineers in the morning.
in the meantime.........i'm outta here to find a glass of wine and a blonde
thanks
gf.







"Nav" wrote in message
...


gonefishiing wrote:


refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

that's what i'm looking for --thanks
although it sounds a higher than i would have suspected and i'll probably
use a more conservative number : something between a pipe section and a box.
if it looks like it approaches anything critical: i'll dig out the actual
moment of interia


gf.

"Nav" wrote in message
...
You can use a simple rule of thumb. If you know the moment of intertia
for a box section of the same wall thickness and outside dimensions the
moment of inertial of the tube or ellipse that has the same dimension is
about 14% less.

Hope this gives you what you want.

Cheers

Well, compare the numbers for a pipe and box section and you will se my
14% rule of thumb...

Cheers

gonefishiing wrote:

that's what i'm looking for --thanks
although it sounds a higher than i would have suspected and i'll probably
use a more conservative number : something between a pipe section and a box.
if it looks like it approaches anything critical: i'll dig out the actual
moment of interia


gf.

"Nav" wrote in message
...

You can use a simple rule of thumb. If you know the moment of intertia
for a box section of the same wall thickness and outside dimensions the
moment of inertial of the tube or ellipse that has the same dimension is
about 14% less.

Hope this gives you what you want.

Cheers

Nav wrote:
Well, compare the numbers for a pipe and box section and you will se my
14% rule of thumb...

Do you suppose there might be a scale effect?

Do you know what that is?

DSK

Quiet Doug. People who understand engineering are talking.

Cheers

DSK wrote:
Nav wrote:

Well, compare the numbers for a pipe and box section and you will se
my 14% rule of thumb...


Do you suppose there might be a scale effect?

Do you know what that is?

DSK

Nav wrote:
Quiet Doug. People who understand engineering are talking.

In other words, you have no clue. Again.

If one could get the Imm of a section by using simple multiplication on
the result of another different section, then why would anyone ever use
calculus? Why all the fancy symbols and stuff?

Oh wait, I know... to impress superstitious fools like you.

You can't even identify all the forces on a simple free body diagram.

DSK