<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD> <META http-equiv=Content-Type content="text/html; = charset=windows-1252"> <META content="MSHTML 5.50.4134.600" name=GENERATOR> <STYLE></STYLE> </HEAD> <BODY bgColor=#ffffff> <DIV><FONT color=#000080></FONT> </DIV> <BLOCKQUOTE style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV> <DIV style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: = black"><B>From:</B> <A title=Erwinspiano@AOL.COM href="mailto:Erwinspiano@AOL.COM">Erwinspiano@AOL.COM</A> </DIV> <DIV style="FONT: 10pt arial"><B>To:</B> <A = title=pianotech@ptg.org href="mailto:pianotech@ptg.org">pianotech@ptg.org</A> </DIV> <DIV style="FONT: 10pt arial"><B>Sent:</B> May 06, 2002 5:31 = PM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Curve on Bridge = Bottom</DIV> <DIV><BR></DIV><FONT face=arial,helvetica><FONT lang=0 = face="Times New Roman" color=#000040 size=3 = FAMILY="SERIF"><I>snip--snip--snip<BR></FONT><FONT lang=0 style="BACKGROUND-COLOR: #ffffff" face=Arial color=#000000 = size=2 FAMILY="SANSSERIF"></I> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px = solid; MARGIN-RIGHT: 0px" TYPE="CITE"></FONT> <BLOCKQUOTE style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff = 2px solid; MARGIN-RIGHT: 0px" TYPE="CITE"><FONT lang=0 style="BACKGROUND-COLOR: #ffffff" = face=Arial color=#000040 size=2 = FAMILY="SANSSERIF">        &nbs= p;           &nbsp= ;            =      Richard, = Terry<BR>          &nbs= p;           It doesn't take much to flatten an unsupported rib as it  = doesn't really take on its maximum stiffness till after it becomes part of = the ply wood componet comprising the whole soundboard system at which = point the cumulative resistive forces of cross banded woods and compression = takes effect....  </FONT><FONT lang=0 style="BACKGROUND-COLOR: = #ffffff" face="Times New Roman Greek" color=#000040 size=3 FAMILY="SERIF"><BR></BLOCKQUOTE><BR><EM>Rather depends on the = cross-section of the rib, doesn't it? </EM></FONT><FONT lang=0 style="BACKGROUND-COLOR: #ffffff" face="Times New Roman Greek" = color=#000000 size=3 FAMILY="SERIF"><BR></FONT><FONT lang=0 style="BACKGROUND-COLOR: #ffffff" face=Arial color=#000000 = size=3 FAMILY="SANSSERIF"><BR></FONT><FONT lang=0 = style="BACKGROUND-COLOR: #ffffff" face=Arial color=#000040 size=3 = FAMILY="SANSSERIF"><EM>Del</EM></FONT><FONT lang=0 style="BACKGROUND-COLOR: #ffffff" face=Arial = color=#000000 size=3 FAMILY="SANSSERIF"><BR></FONT><FONT lang=0 = style="BACKGROUND-COLOR: #ffffff" face="Times New Roman Greek" color=#000040 size=3 FAMILY="SERIF"><BR></BLOCKQUOTE> = <DIV><EM>          &nbs= p;   Yes, but of course,  the stiffening idea of the two componet = forces  combined was what I was trying to illuminate and the thicker the rib = the stiffer the cumulitive effect or perhaps you disagree? Well ,I mean = unless were talking 2 by 4s which would cut the boards contribution  out = of the equation = altogether.<BR>...........Dale>>>>>>>>>></E= M></DIV> <DIV><EM></EM> </DIV></BLOCKQUOTE> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>Let's just say I agree conditionally.... </FONT></DIV> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>The rib--at least in a = rib-crowned board and somewhat simplistically--is an end-supported, center-loaded structural beam. In principle the load-carrying = capacity of this type of beam is a function of the cube of its height. </FONT><FONT face="Lucida Sans" color=#000080>But, its load-carrying capacity is = also a function of the strength characteristics of the material making up = the beam and an assumption is made </FONT><FONT face="Lucida Sans" = color=#000080>that if the height of the beam is increased it will be done so with a material = having strength characteristics that are uniform throughout. </FONT><FONT face="Lucida Sans" color=#000080>Especially in its tensile and = compression strength characteristics. </FONT></DIV> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>When loaded, = this type of rib will be under tension along its bottom surface and under compression = along its top surface. Now, a characteristic of woods such as spruce and = pine is that they have reasonably high compression and tensile strength in line = with their grain but quite poor compression and tensile strength = perpendicular to their grain. </FONT></DIV> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>In the situation you = describe the soundboard panel will be glued to the top of the rib and this will, indeed, increase the overall height of the 'beam' and make the = assembly some stiffer. However, when the assembly is loaded the soundboard = panel--by virtue of its grain orientation at approximately 90º to the rib--will = be placed under compression perpendicular-to-grain. Since its compression strength = in this orientation will be considerably lower than that of the top part of the = rib it will not increase the stiffness of the assembly by the expected = relationship. </FONT></DIV> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>As well, both of these = woods are prone to early compression-set when stressed under compression perpendicular-to-grain. </FONT></DIV> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>So, yes, gluing the = soundboard panel to the top of the rib[s] will increase the stiffness of the assembly. = But not by much and not for long.</FONT></DIV> <DIV><FONT face="Lucida Sans" color=#000080></FONT> </DIV> <DIV><FONT face="Lucida Sans" color=#000080>Del</FONT></FONT></FONT></DIV></BODY></HTML>