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Question 16.12: Determine the equation of the deflection curve of the beam s......

Determine the equation of the deflection curve of the beam shown in Fig. P.16.12. The flexural rigidity of the beam is EI.

Answer:

ν=-{\frac{1}{E I}}\left({\frac{125}{6}}z^{3}-50[z-1]^{2}+{\frac{50}{12}}[z-2]^{4}-{\frac{50}{12}}[z-4]^{4}-{\frac{525}{6}}[z-4]^{3}+237.5z\right)
p.16.12
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Taking moments about D,

R_{\mathrm{A}}\times4+100-100\times2\times1+200\times3=0

from which

R_{\mathrm{{A}}}=-125\,\mathrm{N}

Resolving vertically,

R_{\mathrm{{D}}}-125-100\times2-200=0

Therefore,

R_{\mathrm{B}}=525\,\mathrm{N}

The bending moment at a section a distance z from A in the bay DF is given by

M=+125z-100[z-1]^{0}+\frac{100[z-2]^{2}}{2}-525[z-4]-\frac{100[z-4]^{4}}{2}

in which the uniformly distributed load has been extended from D to F and an upward uniformly distributed load of the same intensity applied from D to F.
Substituting in Eqs (16.31),

u^{\prime\prime}=-{\frac{M_{y}}{E I_{y y}}},\quad ν^{\prime\prime}=-{\frac{M_{x}}{E I_{x x}}}          (16.31)

 

E I\left({\frac{\mathrm{d}^{2}v}{\mathrm{d}z^{2}}}\right)=-125z+100[z-1]^{0}-50[z-2]^{2}+525[z-4]+50[z-4]^{2}

 

E I\left({\frac{\mathrm{d}\upsilon}{\mathrm{d}z}}\right)={\frac{-125z^{2}}{2}}+100[z-1]^{1}-{\frac{50[z-2]^{3}}{3}}+{\frac{525[z-4]^{2}}{2}}+{\frac{50[z-4]^{3}}{3}}+C_{1}

 

E I v={\frac{-125z^{3}}{6}}+50[z-1]^{2}-{\frac{50[z-2]^{4}}{12}}+{\frac{525[z-4]^{3}}{6}} +\frac{50[z-4]^{4}}{12}+C_{1}z+C_{2}

When z = 0, υ = 0 so that C_{2}=0, and when z = 4 m, υ = 0, which gives C_{1}=237.5. The deflection curve of the beam is the

\upsilon=\frac{1}{E I}\left(\frac{-125z^{3}}{6}+50[z-1]^{2}-\frac{50[z-2]^{4}}{12}+\frac{525[z-4]^{4}}{12}+\frac{50[z-4]^{4}}{12}+237.5z\right)

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