Question 11.35: Determine the variation in the depth d of a cantilevered bea...

Determine the variation in the depth d of a cantilevered beam that supports a concentrated force P at its end so that it has a constant maximum bending stress \sigma_{\text {allow }} throughout its length. The beam has a constant width b_{0}.

 

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Section properties:

I=\frac{1}{12} b_{0} d^{3} ; \quad S=\frac{I}{c}=\frac{\frac{1}{12} b_{0} d^{3}}{\frac{d}{2}}=\frac{b_{0} d^{2}}{6}

Maximum bending stress:

\sigma_{\text {allow }}=\frac{M}{S}=\frac{P x}{b_{0} \frac{d^{2}}{6}}=\frac{6 P x}{b_{0} d^{2}}\quad(1)

At x=L, \quad d=h

\sigma_{\text {allow }}=\frac{6 P L}{b_{0} h^{2}}\quad(2)

Equating Eqs (1) and (2),

\frac{6 P x}{b_{0} d^{2}}=\frac{6 P L}{b_{0} h^{2}}

 

d=h \sqrt{\frac{x}{L}}
2

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