고체역학 (Beer) — Shearing Stresses in Beams: Problem 6.4

6.4 Three boards are nailed together to form a beam shown, which is subjected to a vertical shear. Knowing that the spacing between the nails is $s = 75\text{ mm}$ and that the allowable shearing force in each nail is $400\text{ N}$, determine the allowable shear when $w = 120\text{ mm}$.