<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML><HEAD><TITLE>Re: Bridge design</TITLE> <META http-equiv=Content-Type content="text/html; = charset=iso-8859-1"> <STYLE type=text/css>BLOCKQUOTE { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } DL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } UL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } OL { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } LI { PADDING-BOTTOM: 0px; PADDING-TOP: 0px } </STYLE> <META content="MSHTML 5.50.4134.600" name=GENERATOR></HEAD> <BODY bgColor=#ffffff> <DIV><FONT color=#000080></FONT> </DIV> <BLOCKQUOTE dir=ltr 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=kpiano@goldrush.com = href="mailto:kpiano@goldrush.com">Keith Roberts</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> July 08, 2002 9:04 = AM</DIV> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Bridge = design</DIV> <DIV><BR></DIV> <DIV><FONT face=Arial size=2>    A laminate = structure is far more resistant to flex. </FONT></DIV></BLOCKQUOTE> <DIV dir=ltr><FONT color=#000080>Not so. According to the USDA Wood = Handbood: Wood as an Engineering Material, the stiffness characteristic of a = glulam timber is the same as a solid timber of comparable size and grade. That is = assuming that the grain density, freedom from defects, etc., are the same -- and = this is the key. Given today's lumber supply it is very difficult to get beams = of any size that are of clear, uniform stock. Laminating smaller boards of = better grade together overcomes this limitation and the glulam of higher (average) = grade stock is stronger than a solid beam of overall poorer (average) grade stock.</FONT></DIV> <DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV> <DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV><FONT face=Arial size=2>Bend too straight pieces of wood and = glue them together. They want to stay where you glued them and will stay that = way longer and with less warpage than a piece of solid wood cut that = way. (presuming the glue joint....etc.) I've been in the construction trades 30 years and a laminate beam is far more desirable structurally than even = pattern nailing a bunch of boards together.</FONT></DIV></BLOCKQUOTE> <DIV dir=ltr><FONT color=#000080>All this is true, but things like = stability, freedom from warpage, etc., have nothing to do with ultimate strength. = It is these things -- stability, consistency, etc., that make glulams = desirable. Not greater strength. </FONT></DIV> <DIV dir=ltr><FONT color=#000080></FONT> </DIV> <DIV dir=ltr><FONT color=#000080>Our own experience bears this out. = We've been using laminated Sitka spruce ribs for many years and our direct = comparative tests have not indicated that they are any stiffer than comparable solid = Sitka spruce ribs. They do have many characteristics we find to be desirable, = but greater stiffness is not one of them.</FONT></DIV> <DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV> <DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV><FONT face=Arial size=2>    Now here's where I = may be presuming two much. It seems to me, as the bridge is loaded and the soundboard/bridge structure approaches the point of failure, the = impedance would change exponentially. </FONT></DIV></BLOCKQUOTE> <DIV dir=ltr><FONT color=#000080>I can't imagine how a = bridge/soundboard assembly could possibly be loaded to anything close to its point of = failure. Relative to their ultimate load-carrying capacity these systems are very = lightly loaded.</FONT></DIV> <DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV> <DIV dir=ltr><FONT face=Arial size=2></FONT> </DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV><FONT face=Arial size=2>Small initial changes can become = major. In my limited experience I haven't heard of any real model test of 2 = identical boards and bridges glued up and run through a battery of tests. It was = my feeling (my 2 1/2 years of engineering at UCSB is now a jigsaw puzzle = with a bunch of missing pieces), that the glue joint as a variable might not = have been correctly assessed.</FONT></DIV></BLOCKQUOTE> <DIV dir=ltr><FONT color=#000080>I'm unconvinced that the glue joint = has much of anything to do with the ultimate performance of the bridge/soundboard system.</FONT></DIV> <BLOCKQUOTE dir=ltr style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; = BORDER-LEFT: #000080 2px solid; MARGIN-RIGHT: 0px"> <DIV><FONT face=Arial = size=2></FONT> </DIV></BLOCKQUOTE></BODY></HTML>