RC vs CC again

[Richard Brekne]

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Delwin D Fandrich wrote:

>
> > All of this suggests to me that in general, a CC board has an easier
>
> > time generating a higher stiffness to mass ratio...as long as the
> > compression in the panel holds. Yes ?
> >
> > RicB
> -----------------------------------------------------------------------
>  No. Remember the stiffness of the ribs increases directly with its
> width but with the cube of its height:
>
> [Image]
>
> Grin... now THATS what I'm talking about !!...  Seriously tho... this
> is easy enough to follow. Do you have a similiar formula for how much
> stiffness the assembly takes on for panel compression ?..
>
> And.... well.. you could always increase height of the ribs in a CC
> board as well... but then... that wouldnt make much difference given
> that the ribs dont do a lot to support the pannel.
>
> So.. what.... the ribs function in a CC board is primarilly to force
> the panel into compression ?? Why the choice of fat and not so high
> instead of lots of height... or something else... what determines your
> choice of rib dimensions in a CC board ?
>
> y = deflection of beam (measured at center)
> K = a constant (0.25 for a center-loaded beam)
>
> P = load on beam (at center)
>
> E = modulus of elasticity (1.57 x 106 for Sitka spruce)
>
> l = length of beam
>
> b = width of beam
>
> d = depth of beam ... and we get to manipulate both the height and the
> width of the rib. I can make that rib enormously stiff before I run
> into mass problems. Del

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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