R,C&S question JD

[John Delacour]

At 09:38 +0100 27/1/08, Richard Brekne wrote:

>...there is a stated goal of applying enough downbearing so that 25 
>% of the unloaded crown remains after stringing.

First of all, I won't question this figure simply because I haven't 
time to trawl the archives for a statement to this effect, but it 
would be good to have confirmation from one of the practitioners that 
this is so.  It seems unlikely if I'm not mistaken in what follows.

I think it would be useful first to have a true figure from one of 
the RCS-heads for the radius of curvature  of the belly at a point 
where the rib is say, 1 metre long instead of the extreme cases given 
by Terry F. and Ron N.

_____________________

At 22:04 +0000 19/1/08, John Delacour wrote:

>I have exaggerated the crown to a radius of 15ft.  The length of the 
>section is 500 mm.

At 19:07 -0500 19/1/08, Farrell wrote:

>What's exaggerated about a crown radius of 15 feet?

At 14:20 -0600 23/1/08, Ron Nossaman wrote:
>And no, 15' isn't an excessively tight radius for a machine crowned 
>rib. I go down to 4 meter in the treble, Whatever Wolfenden has to 
>say about it.
_____________________

If the unloaded radius of the crown were 4 meters at a point where 
the rib were 1 metre long, then the height of the crown would be 31.4 
mm and to reduce that to 25% would mean a lowering of the apex of the 
crown of 23.5mm and an increase in the radius of curvature to 16 
metres, and one begins to count elephants.


>  That strikes me as equating to a good deal of compression in the panel.

And the rest!

>  Looking around these past few days and asking questions in a 
>variety of places... I'm left wondering if there IS any direct way 
>of figuring just how much compression a given lateral load on a beam 
>will build up in the panel.

To calculate the all this properly requires the calculus, as all 
these things do, but a more easily understandable rough calculation 
can be done using simple geometry.  Then, in order to get an idea of 
the physical effects of the changed geometry, we have Hooke's law, 
Young's modulus etc.  But it is pointless making calculations until 
some real figures are forthcoming from one of the RCS people.

JD