고체역학 (Beer) — Shearing Stresses in Beams: Problem 6.51

6.51 The design of a beam calls for connecting two vertical rectangular $\frac{3}{8} \times 4\text{-in.}$ plates by welding them to two horizontal $\frac{1}{2} \times 2\text{-in.}$ plates as shown. For a vertical shear $V$, determine the dimension $a$ for which the shear flow through the welded surfaces is maximum.