Laminated panels (Farrell)

[Jude Reveley/Absolute Piano]

Hi Terry,

> Jude - Regarding your concern about horizontal shearing stress. Is that 
> concern that the panel or rib might fail or degrade in some way as a result 
> of whatever shearing stresses might be present? Is your concern that these 
> items might fail or degrade more readily than a solid item?

I think so. When I think of a composite structural member supporting a floor or a ceiling, I know the beam is engineered to resist any potential load by a significant factor. This would be too stiff in a piano sb design, so I would be concerned that the shearing strain from the string bearing load might be an issue if not in delamination than checking the cross grain laminations. Then again, the only problem might be my understanding of the problem and I'm looking at addressing this presently. Give me some time.

> 
>>From what I've experienced, building these items with adhesives such as 
> Titebond yields excellent results. Some folks would have concerns regarding 
> glue "creep" with Titebond. I don't, but if one did, build the panel or ribs 
> with a glass-hard adhesive like two-part urea-formaldehyde. Is "creep" where 
> your concern center? I used a modified two-part urea-formaldehyde adhesive 
> on the panel that Richard Brekne wrote about. Certainly the bond with that 
> adhesive is way stronger and sheer-resistant than the wood itself. And with 
> respect to the panel, I should think that crossing grain angles between 
> laminations would also make the entire assembly more resistant to stress 
> from any direction - including sheer.
> 
> Just my thoughts, FWIW.
> 
> Terry Farrell 
>
That's a very good and focused question. I don't think my concern is with the creep but perhaps with the adhesive. Perhaps I'm just being a nervous Nellie and if the load does not exceed its demands, we're ok. You also have the advantage of the assembly being attached at both ends (I have even more concern about a laminated key that is working as a cantilever, but then the loads aren't so great here). I'll get back to you when I have a clearer understanding of what I've read on the subject and have perhaps made some experiments myself. Man I wish I had some of those cool devices Mr. Hoadley has at UMass.


Jude
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