$1-95.$ The pin support A and roller support $B$ of the bridge truss are supported on concrete abutments. If the bearing failure stress of the concrete is $({}_{\text{f}\text{a}\text{i}\text{l}}{)}_b=4$ksi, determine the required minimum dimension of the square bearing plates at $C$ and $D$ to the nearest $\frac{1}{16}$ in$.$ Apply a factor of safety of $2$ against failure.

$a_D=19\mathrm{.}58in.a_C=21\mathrm{.}02in$