Bridge design

[Erwinspiano@AOL.COM]

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>  
>          Keith Roberts wrote
> >> 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.
>> Del wrote
> 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. 
>  
> 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.         Del
> 
>   Del
>       Then why go thru the trouble of laminating ribs except it's a good 
> use of otherwise unusable spruce or the design characteristics are vastly 
> superior. It's a good deal more work

      Since no one asked the obvious question earlier there must be some very 

> desireable attributes to laminated ribs to compel one to do this routinely. 
> For me the jury still's still out.

       So far all I can determine with my limited experience with Glue 
> Lam. ribs is that,
>   When I've done this I've laminated three or four pieces of quartered 
> sitka in my soundboard press. Instant 60ft crown glued in, but the process 
> is a bit messy. I thought that the ribs seem to be more uniformly stiff 
> though.
>   Also the rib is uniformly thick like old  flat ribs only nicely bent into 
> an arch/arc negating the cutting of the ribs radius unless a different one 
> is desired.
             Laminated ribs aren't thicker in the middle than on the ends as 
are crown/radius cut ribs. Desirable or not? Dunno yet.
  I didn't find the ones that I did too have any better tone than the no 
laminated boards. I've also Found that white spruce to be far stiffer and 
more uniformly stiff than Sitka (which seems to vary greatly). Hmm another 
reason to laminate.
       Any secrets left. Don't feel obligated
.                                Dale Erwin
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