User talk:Athosanian

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Hello. As alluded to in the section you cite, the Euler-Bernoulli beam theory accounts for deflections due to beam bending (i.e., due to internal moments), but it does not include deflections as caused by internal shear forces. For long and slender beams, the effects of internal moments are usually much more pronounced on the overall beam deflection than the effects of internal shear forces. To really know when the shear forces are important (i.e., when the beam is no longer a "thin beam"), it is necessary to compare results obtained using the Euler-Bernoulli beam theory with a more advanced theory such as the Timoshenko beam theory (which does include shear force effects). A general "rule of thumb" is that when the ratio of the beam's length to it's thickness is less than about 20 (Theory and Analysis of Elastic Plates and Shells, J. N. Reddy), shear forces are significant and the beam is no longer "thin". For a more rigorous assessment, it is necessary to consider specific boundary and loading conditions for the particular beam in question. However, I think the rule of thumb I mentioned (L/h > 20 => thin beam) is a pretty good assumption for most circumstances. I hope this is helpful for you. Gpayette (talk) 18:12, 6 May 2009 (UTC)