Gene Nelson wrote: > > > > > 1- deflection of an individual stand alone rib unattached to any > bridge structure is quite linear and conforms to the deflection > formulae. > 2- the addition of the bridge adds significant stiffness to the > structure. This was not intuitive for me. The bridge not only > evens (bridges) the loads, but it actually adds stiffness to the > rib assembly. > > > Is the measured deflection described in (#1) and additional > stiffness described in (#2) the same measurements? > No. #1 is simply measuring deflection at an individual rib, glued to the rim at the bearing points. Measurement taken before and after the specified load was applied to that single rib. At this point in the test, the bridge had not been glued to the ribs yet. #2 the bridge was glued to the ribs. Deflection was then measured at each rib again. This measurement was taken at each rib, first, before any loads were applied to any of the belly and second, after all the loads for the entire belly had been applied to their respective ribs. The deflection in #1 agreed within 10% or so with the simple beam deflection formula. The deflection in #2 was app 50% less than what was predicted by the above simple beam deflection formula. All the ribs in the entire belly structure exhibited this app 50% reduction in deflection once the bridge was glued on, so the reduction doesn't seem to have been caused by a load leveling effect of the bridge. The fact that #2 deflected much less with the same applied load is what prompted me to say the bridge stiffened the structure. *****However******My test results were on a 1/3 scale belly without a soundboard panel. I really don't have the evidence to say this is what happens in a full scale belly which includes both a soundboard panel and bridge. Of the points made in my post, this point is the weakest, and needs to be validated or refuted by your own experiments. THE point of the post was to pay attention to trends. I hope this trending point makes it past any shortcomings in the post. Jim I grandpianosolutions.com ps paul, here are the pics of Version 1 of the test. Version 2 had a revised rib scale and 7 times as much weight approx 55.4lbs scaled from 500lbs @ 1/3^2 (formula courtesy of Ron) -------------- next part -------------- A non-text attachment was scrubbed... Name: loads applied.JPG Type: image/jpeg Size: 162379 bytes Desc: not available URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100105/af72c2fa/attachment-0002.jpeg> -------------- next part -------------- A non-text attachment was scrubbed... Name: ribbridge testversion1.JPG Type: image/jpeg Size: 153622 bytes Desc: not available URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100105/af72c2fa/attachment-0003.jpeg>
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