I'm looking for established limits or rules of thumb for the validity/accuracy of Euler-Bernoulli beam equations for particularly wide "beams". For example, a simply supported rectangular plate where the breadth(b) is much larger than the height (h) [e.g. b=120 inches, h=1 inch].

Is there a point at which a simply supported beam where b >> h would deflect more like a plate in plate theory rather than a beam in beam theory? If you can, please provide references. Thank you!

  • $\begingroup$ May find checking out Timoshenko beams useful. $\endgroup$
    – Solar Mike
    Aug 25, 2020 at 16:24

1 Answer 1


For a rectangular simply supported plate with length $a$ and width $b$ (Roark's Formulas for stress and strain):

$$\sigma_{max} = \sigma_b= \frac{\beta qb^2} {t^2} $$

$\beta$ ranges from 0.287 for a=b to 0.75 for a very long and narrow beam. 0.75 would make it equal to a beam. At a=5b ,$\beta$ is 0.74.

Approximately at $a> 5b$ the plate behaves very similarly to a beam.


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