Hardwood equivalents for HYspan beams

[glock40sw]

Sorry.
Wrong timber site .

try this


http://www.timber.org.au/menu.asp?se....02%20Software

[Dr - 307]

Thanks glock,

That'll come in handy.

Cheers,
Dr - 307.

[DvdHntr]

Mick
at the risk of getting us both into deep trouble, the strength of a beam is related to a property called the Second Moment of Area (often refered to as the Moment of Inertia)

For a rectangular beam the second moment of area is calculated as

<DL><DD> </DD></DL>

• b = width (x-dimension),
• h = height (y-dimension) (thanks to Wikipedia for the formula)

this value along with the strength of the material used for the beam is used to work out how much deflection (bending) a beam will experience when loaded.
I'd have to go back to the books to find the exact formulas used but a bit of number crunching with "standard" sections and assumed "normal" loads then gives you the span tables we all look up.


but back to your question the I(x) value for a
225 x 100 is (100 x 225 x 225 x 225 / 12 =) 94,921,875 which would usually be rounded to 94.9 million
250 x 75 is (75 x 250 x 250 x 250 /12 =) 97,656,250 which would be rounded to 97.6 million

94.9 and 97.6 are near enough the same, so the span tables consider them to be equivalent sections


ian

That is all well and good but the first line in your post is incorrect. Beam Stiffness is what you are referring to and it is a function of the I and the E (youngs modulus) which is a measure of the material. For steel E is 200000MPa; Hardwoods between 18500 and 14000 and Softwoods less.

EI is the stiffness and it determines deflection resistance.

Strength of beams is actually related to the second power of depth but also to the restaints and the grade.

[Dr - 307]

Someone!!! Quick!!! Give me Alan Staines book!!!

Now I know what just flew over my head.

Doc.

[DvdHntr]

Please do not assume that beam stiffness will always govern design.

[ian]

DvdHntr

I think we should be careful not to turn this into a too technical discussion.

These forums generally talk about residential construction where beams typically span windows and door openings, or substitute for the removal of a load bearing wall.
in these cases the "visual" aspects of the design usually govern — get the deflection "wrong" and the window / door wont close properly, or the ceiling line will have a noticeable "woof" in it.
Rarely do questions relate to the load bearing capacity of a timber beam


ian