laminated ribs

[William R. Monroe]

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




----- 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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