Large or small deflections of a cantilever beam

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Discussion Overview

The discussion revolves around the applicability of classical bending theory to cantilever beams under various loading conditions, particularly in the context of determining the first natural frequency of the beam. Participants explore guidelines for when to use classical beam theory versus Timoshenko beam theory based on beam dimensions and deflection.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks guidelines for applying classical bending theory to cantilever beams in their dissertation work.
  • Another participant suggests that classical beam theory (Euler-Bernoulli) does not account for shear strain, which could affect the accuracy of the natural frequency estimation, recommending Timoshenko beam theory instead.
  • A further reply outlines specific conditions under which classical beam theory can be applied, stating that it is generally applicable if the beam length L is greater than or equal to 10 times the cross-sectional depth h.
  • The same participant notes that if L is less than 10*h, Timoshenko beam theory may be more appropriate.
  • They also mention that small deflection theory can be used if L is greater than or equal to 10 times the maximum bending deflection y.
  • For clamped or embedded beams, they suggest adjusting the criteria to a factor of 20 instead of 10.

Areas of Agreement / Disagreement

There is no clear consensus on the applicability of classical versus Timoshenko beam theory, as participants present differing views on the conditions for their use. The discussion remains unresolved regarding the best approach for specific scenarios.

Contextual Notes

Participants reference specific ratios and conditions for applying beam theories, but the discussion does not clarify the assumptions or limitations of these parameters. There is also a request for references to support the claims made about these parameters.

fmsrat
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Hi,

I'm looking for a parameter or a design guideline that could say weather or not the classical bending theory can be applied to certain beam under certain load. I'm making my dissertation about some work on cantilever beam and it's first natural frequency, so in order to model correctly the beam i would like to know if could use the classical bending theory.

Thanks in advance
 
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fmsrat:

From what I remember, using the classical beam theory (euler-bernoulli) does not account for shear strain which would over or under estimate your natural frequency. I feel that the beam theory you should be looking is Timoshenko.

Again, this from what I remember. Hopefully someone can correct me if I am wrong.

Best of luck.
 
fmsrat: (1) For a cantilever beam, you generally can use classical beam theory (Euler-Bernoulli beam theory) if beam length L ≥ 10*h, where h = beam cross-sectional depth.

(2) For a cantilever beam, if L < 10*h, you might want to use Timoshenko beam theory.

(3) For a cantilever beam, you generally can use beam small deflection theory (i.e., basic Euler-Bernoulli or Timoshenko beam theory, mentioned in items 1 and 2) if L ≥ 10*y, where y = beam maximum bending deflection.

(4) For a http://img72.imageshack.us/img72/9576/beam02.png or http://img600.imageshack.us/img600/3467/beam03.png (clamped, embedded, encased, encastre, built-in) beam, change each 10 to 20 in items 1, 2, and 3, above.
 
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Thanks for your reply, could you tell me what references(articles,books) did you use for that parameters.
 

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