고체역학 (Beer) — Shearing Stresses in Beams: Problem 6.2

6.2 A square box beam is made of two \(\frac{3}{4} \times 3.5\)-in. planks and two \(\frac{3}{4} \times 5\)-in. planks nailed together as shown. Knowing that the spacing between the nails is \(s = 2\) in. and that the allowable shearing force in each nail is 75 lb, determine (a) the largest allowable vertical shear in the beam, (b) the corresponding maximum shearing stress in the beam.