Crown, was RE:Curve on Bridge Bottom

[Richard Brekne]

Ron Nossaman wrote:

> >So, just chewing on this one  a bit.... take your rib # 5 at 9.4 mm crown...
> >that gives a rib length of 1163.291262 mm for an 18 meter radius. With a
> >segment angle of 3.7 degrees that gives an arc length of 1163.49380 mm
> yeilding
> >a difference of 0.2025412 mm or roughly 0.008 inches.... no ??
>
> Looks right... and?
>
> Ron N

Just trying to figure out why Dale got the notion that the panel would spread by
0.05 " (1,27mm).  I suppose he must have been imagining how much crown there was
on a panel that was newly ribbed / pressed / crowned.... and perhaps just
"assumed" it would have to extend so much when pressed flat.  I thought it might
be illustrative to take a look at what parameters would have to be present to
allow for that much spread.

Sticking with an 18 meter radius.... Looks like you'd have to have a rib of
around 2150mm (gives an arc of 2151.28mm). This rib length would also mean a
crown of a whopping 128.86 mm to achieve that much spread. Thats like a 5 inch
crown!  Its late and I am not going to run these numbers again so I coulda zigged
when I shoulda zagged.... but if these hold then its easy to see why one would
imagine that a given crown would result in more spread then it actually does.



--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html