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Terry... et al
<p>I wanted to get back to you on this with a better explaintion of what
bothers me about this position you take below.
<p>Consider the following.
<p>When ever a board is bent the, convex side will be stretched relative
to the concave side. This is the same regardless of the over all compression
level found in the board. Pressing downwards on this curved board
will tend to have the opposite effect... ie stretch the concave side and
compress the convex side.
<p>Ribs glued to the concave side will fight any tendency of the panel
to stretch on its concave side. Thats what causes them to bend in the process
of crown formation in the first place. Downbearing applied to the
convex side of the panel will tend to compress the convex side, and stretch
the concave side... but the ribs resist stretching of the concave side.
<p>So how does that equate to
<blockquote><font face="Arial">"As the crown lessens under increasing load,
the ribs will pull downward a bit less, but only because they are being
bent upwards less by the panel."</font></blockquote>
?
<p>Seems to me the ribs will be even more stressed by down bearing...erg
they support crown against applied downbearing.
<p>Yes ???
<p>RicB
<p>Farrell wrote:
<blockquote TYPE=CITE><style></style>
<font face="Arial">Richard wrote:</font> <font face="Arial">"This
assertion that ribs don't support the bearing load also is bothersome.
Why</font>
<br><font face="Arial">wouldn't the ribs in a CC board support both crown
and bearing... just because the</font>
<br><font face="Arial">panels compression forces the ribs to bend?"</font> <font face="Arial">When
flat ribs are glued to a very dry flat panel, no force vectors exist in
the system. As the panel takes on moisture and the ribs bend, the ribs
will <i>always</i> be trying to pull the panel flat. Period. If that assembly
has crown, the ribs will <i>always</i> try to go straight by pulling down
on the panel. The compression forces in the panel are the only thing that
has provided the force necessary to bend the rib into a crown. Whether
or not you ever load that soundboard on top, the ribs will always be fighting
the panel compression to go flat. When you do apply a load to the top of
the soundboard, the compression on the panel will increase, but the ribs
will do nothing other than still try to go flat. As the crown lessens under
increasing load, the ribs will pull downward a bit less, but only because
they are being bent upwards less by the panel.</font> <font face="Arial"></font> <font face="Arial">Terry
Farrell</font> </blockquote>
<p><br>--
<br>Richard Brekne
<br>RPT, N.P.T.F.
<br>UiB, Bergen, Norway
<br><A HREF="mailto:rbrekne@broadpark.no">mailto:rbrekne@broadpark.no</A>
<br><A HREF="http://home.broadpark.no/~rbrekne/ricmain.html">http://home.broadpark.no/~rbrekne/ricmain.html</A>
<br><A HREF="http://www.hf.uib.no/grieg/personer/cv_RB.html">http://www.hf.uib.no/grieg/personer/cv_RB.html</A>
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