WOODWORKING QUIZ for 28 June 04

[Ralph Jones]

Good Evening Friends,
Please figure the answer to this quiz in pounds.

What would be the safe load in pounds for a built-up beam for floor joists of 6 x 8" spanning 10'?

Respectfully,

[bitingmidge]

Ralph,

We went metric in currency in 1966, so no longer have pounds, shillings or pence!!

Not enough information I'm afraid. (even if I was capable of calculating the result)

We'd need to know the strength of the timbers.

In the old days when we just had ungraded green hardwood, it was a bit stronger than the stuff you are used to dealing with. The old rule of thumb for a residential joist at 600 centres was "half the span in feet plus one = the inches deep x 2" wide" so for a 10 foot span we'd be using a 6 x 2, except that we'd probably drop the span to 8' and use a 5 x 1 1/2 .

A bearer was the same but an inch wider.

None of that counts any more, we have stress grades and engineers and stuff....200 years without a failure and they go and change the system!

Cheers,

P

[Bob Willson]

Have to agree with biting again. Not enough information. How wide is each safe, who made them and what is the model number. With this information we should be able to get the full specs on each safe and give you a definite answer to the problem.

[Ralph Jones]

Good Evening Friends,
To answer your questions, each beam was joined together using 2 x 8 safes or timbers and building up a beam that would end up being 6" x 8" and would span 10'.

Now according to the table indicating the typical safe loads for standard size wood girders. A 6 x 8 girder spanning 10' should be capable of supporting 4062 pounds (aviordupois) = 1842.49 Kilograms.

Thank you for your interest and support.

Respectfully,

[Robert WA]

"(aviordupois)"
Avva what? I'll avva beer.

[Ralph Jones]

Hello Robert,
To be honest, I don't know what it means either as I never took Greek in school.
I thought it was a term you blokes used in the land down under.

All I know is that is what was printed in the information that I got from the conversion link that you gave me a little while back.

I'm as confused as you are.

Respectfully,

[Bob Willson]

Avoirdupois: Goods sold by weight, from Old French, literally, goods of weight

[Ralph Jones]

Hello Bob,
Thank you for clearing that matter up, now we all have learned something.

Respectfully,

[bitingmidge]

Sorry Ralph,

Can't agree...not that I have done the sums...but surely the end result will depend entirely on the strentght of the timber which has been used.

To an extreme, a beam of balsa wood or even western red cedar may need to be just a bit bigger than one made of one of our very dense hardwoods.

There are a number of answers depending on the timber to be used.

Cheers,

P