laminated ribs

[Nichols]

At 02:10 PM 2/17/2006 -0600, you wrote:
>Guy,
>
>If two-plies have similar bending stress characteristics, what happens as
>the number of plies increases?  Do more plies give greater resistance to
>bending stress?  What about break strength?  Forgive me if I failed to get
>this from previous posts.  I assure you it was not for lack of trying...
>:-].
>
>Regards,
>William R. Monroe
>

William,
     Simply put, to answer most of your questions, plywood is "stronger" 
than equally dimensioned solid wood. VERY simply put. It doesn't mean that 
three plies of sugar pine will be stronger than an equal size piece of 
hickory.
    In construction of structural multi-laminates, there are many factors 
that affect bending resistance and breaking strength. Advantages of 
multi-lam are numerous, from economy to weight -to-strength ratio, and on 
and on, etc.
   I was, in my earlier post, addressing Terry's question (or trying to):
"I suspect the solid beam might reach failure at a lighter load than the 
laminated beam, but I don't see why the strain in relation to stress would 
differ."
    The point of my ramble ('cause it wasn't really an answer) was to point 
out that there is a "limit" to the improvement, or at least to the overall 
value of the improvement, of a multi-lam. An example is belly beams. If you 
look at various beams in big grands, you're more likely to find thicker and 
fewer (like...uh... 3) plies applied. Again, so many factors involved, when 
you're not talking in very general terms.
    For ribs, I think it's a no-brainer, if for no other reason than the 
fact that it is LESS WASTEFUL!
Basically..... that's good enough for me.
<G>

Later,
Guy




>----- Original Message -----
>From: "Nichols" <nicho@zianet.com>
>To: "Pianotech List" <pianotech@ptg.org>
>Sent: Friday, February 17, 2006 11:33 AM
>Subject: Re: laminated ribs
>
>
> >
> > Terry,
> >     In both beams, solid and laminated, the beam is a "system". When you
> > add up the parts of the whole, bending stress and breaking strength vary
>at
> > different values. The difference in variance changes dramatically with the
> > overall difference between systems. A two-ply lamination will have very
> > similar bending stress characteristics, but the breaking strength will be
> > more different. As the number of plies increases, the variance changes, of
> > course, but not as much. A dozen variables make it difficult to call it
> > logarithmic, but it's basically a case of diminishing returns for bending
> > compared to improved breaking values. If I recall correctly. It's
> > been...... decades.
> >
> > Guy
> >
> >
> >
> > At 10:41 AM 2/17/2006 -0500, you wrote:
> > >>>>I'm with you on ease of crowning, accuracy and more uniform
>statistical
> > >>>>average MOE from batch to batch. But why would a laminated beam have a
> > >>>>higher average MOE than a similar solid beam?
> > >>>>
> > >>>>Terry Farrell
> > >>>
> > >>>
> > >>>I'm not sure, but they seem to. I tested this once and recall finding
> > >>>that to be the case, but it's been a while so I might be mistaken.
> > >>>Memory leaks, and such.  Maybe it's time to do it again.
> > >>>
> > >>>Ron N
> > >>
> > >>
> > >>No Ron you're not mistaken. Laminated beams have a higher MOE.
> > >
> > >Let's see where this goes.
> > >
> > >>Relative to a solid beam, the internal stresses which occur naturally in
> > >>the growing tree are largely dissipated when the individual layers are
> > >>joined back to form a whole.
> > >
> > >Yes, I see that and agree.
> > >
> > >>One only has to watch sawn strips warping all over the place as they
>come
> > >>off the saw to realise what must be going on inside the full piece prior
> > >>to resawing.
> > >
> > >Amazing, isn't it? And a bit scary! But sure, I see that all the time.
> > >
> > >>Think a tug-of-war analogy. With five strong people of nearly of equal
> > >>strength, at either end of a rope, it will only take a small addition
> > >>plus or minus to topple the balance in one direction. If those five
> > >>strong people were all working together holding a bar firm, for example,
> > >>it would take much more than a small force to move the bar.
> > >
> > >True.
> > >
> > >>Similarly, the various sectors of wood in a solid beam are not acting to
> > >>support a given load.
> > >
> > >I'm not sure I understand that.
> > >
> > >>Some will be trying to move with the load while other sectors will be
> > >>supporting it.
> > >
> > >Yes, agreed. Some vectors may be supporting the load more than a neutral
> > >piece, while others will offer less than neutral support. So wouldn't
>that
> > >mean a net stress vector of zero? Just like with the laminated beam, if
> > >the solid beam is not bending on it's own (unloaded), the net strain is
> > >zero, and hence the net stress is zero. If a load is applied, seems to me
> > >the two types of equally dimensioned beams would have a similar ability
>to
> > >support, i.e. similar MOE.
> > >
> > >>If a similarly dimensioned laminated beam was used to resist a load a
> > >>much higher proportion of the beam will be working to support the load.
> > >>Hence the higher MOE in the laminated beam. Hope that makes sense.
> > >
> > >No, it doesn't. But that may just be me. Seems to me that if beams of the
> > >two types with no load will have a net strain of zero and thus should be
> > >able to support similar loads. I understand your point of the greater
> > >internal stresses in the solid beam, but if they cancel out (which them
> > >must if the solid beam is straight), there is no net stress and it will
> > >behave similar to the laminated beam. I suspect the solid beam might
>reach
> > >failure at a lighter load than the laminated beam, but I don't see why
>the
> > >strain in relation to stress would differ.
> > >
> > >Care to try prying through my thick skull again? Or maybe I just need to
> > >take a few beams and apply some loads. I'll try to do that this weekend.
> > >
> > >Terry Farrell
> > >
> > >>Ron O.
> > >>OVERS PIANOS - SYDNEY
> > >>    Grand Piano Manufacturers
> > >
> > >
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> > >
> >
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>
>
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