[pianotech] was crown and radius now displacement under load

[Gene Nelson]

Back at the drawing board while cosidering the desired rib dimensions:
"assuming a soundboard with quartered sitka ribs - radiused and sized to 
support a known string bearing load- the piano is strung and up to tension 
so the board is loaded and at equalibrium."
What is a good way to describe or include into rib design how much the board 
is displaced when set in motion by the strings? How important is it to rib 
design?
A forte blow could displace a bass string by a couple mm at least depending 
on the hammer mass. Not certain but amplitude maybe should describe this? 
Not certain how to measure it.
Is it reasonable to assume the board/rib will move a distance down and up 
that is equal to amplitude? Could it possibly move more? It probably will 
move somewhat less??
Does anyone include this sort of thing in rib design?
Certainly the motion of the board is more complex than just down and up but 
it is simple for me to look at it this way.

One thing that I have discovered by playing with numbers is that the 
available crown of a rib could be completely used up or even exceeded and 
the rib's fspl is not exceeded depending on its dimensions. So - if a rib 
has xmm of crown and 50% is taken up by the downbearing or string bearing 
load, in a static situation is it possible that additional rib motion due to 
the amplitude of the string become a sturctural issue? Seems to me it could.

Gene