$4\mathrm{.}3$ Assuming that the static$-$deflection curve is the same as the first$-$mode shape and including only that mode, compute the maximum dynamic bending moment in the beam of Fig. $4\mathrm{.}18$c due to the load$-$time function of Fig. $4\mathrm{.}20.($Note: Figure $2\mathrm{.}7$ may be used.$)$

Figure $4\mathrm{.}20$ Problem $4\mathrm{.}3.$ Load$-$time function.

Figure $4\mathrm{.}18$c

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