Hi Terry Not quite me thinks, (at least as I think I understand what you are getting at). Certainly downward pressure on the ribs alone exert a stress (force) that will eventually strain the ribs. But even in RC&S systems pressure downwards on the combined assembly will stress the interface between the ribs and soundboard. And this is where it gets interesting. On the one hand the downward pressure on the ribs (if seen isolated from the assembly) will exert a compression stress on the top half of the rib. But on the other hand that same downward pressure will exert a compression stress on lower half of the soundboard, and compression there will in turn stress the ribs in a tensional direction. So downward pressure on the entire assembly places two and opposing types of stress on the ribs (and the soundboard ftm) Now one can rightly state that the ribs resistance to tension is several mulitples of that of the panels resistance to compression. However as stated in my last post, it is not greater then that the ribs upper half actually does strain tensionally when the panels under side compresses enough for the assembly to experience a strain in its crown. Which of the opposing stresses wins out in the ribs case is less interesting then the fact that the result would be different if the rib was isolated from the assembly and experienced only a downwards strain. Grin... and I think I've managed to keep the stress-strain-compression-tension- words all in their proper contexts... must be learning :) Cheers RicB Terry Farrel writes: stress is the force causing the deformation divided by the area to which the force is applied; and strain is the ratio of the change caused by the stress to the original state of the object. For a piano rib (in a RC&S system) then, the stress would be downbearing and the strain would be the amount of crown loss due to downbearing pressure. Terry Farrell
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