Ron Nossaman wrote: > >I don't understand the logic of "...the underside of the panel will want > >to expand when down bearing is applied...". What leads you to that > >conclusion? Why would the underside of the panel want to expand? The > >entire thickness of the panel would compress I should think. > > > >Maybe I'm all wet here, but that's what makes sense to me. Anyone else > >care to chime in? > > > >Terry Farrell > > Yes, the whole panel will compress. There will be a neutral line somewhere > in the rib that is neither under compression, nor tension. Below that line, > the rib will be under compression, and above that line, the rib will be in > tension (until the crown is gone and the rib is flat). If there is compression in the panel.. then there must be tension in the top side of the rib. One causes the other and vice versa.. with out the one there is neither. Sure the whole panel will compress. Pushing down on the panel increases that compression because it increases the stresses between the panel and the ribs.... as in both the panel and the ribs. The entire panel will be subjected to increased compression, and the entire rib will be subject to increased in the corresponding tensioning forces. The rib ends up flater no doubt... but just a tad longer too. Not much perhaps... but enough to make a difference. > The panel is > entirely above this line, and will be entirely under compression as long as > it can hold the rib up. It is exactly what it appears to be, panel > compression levering the rib into a crown. The panel is supporting all the > load, and the rib is supporting none, instead adding to the load the panel > must support. > > Ron N > What this adds up to is that somehow or another... just because the panel gets pushed flat... the panel can remain stressed big time (compressed) yet all the stresses in the ribs have just disapeared... no tension in the top and no compression in the bottom. I dont see how a rib can get into this state... where it is exerting a huge compression force on the panel, while not experiencing a tensioning force in return. I'm not saying it isnt possible... I'm just saying I dont see how that can be. RicB -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html http://www.hf.uib.no/grieg/personer/cv_RB.html
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