고체역학 (Gere) — Stresses in Beams (Advanced Topics): Problem 6.2-5

6.2-5 A hollow box beam is constructed with webs of Douglas-fir plywood and flanges of pine, as shown in the figure in a cross-sectional view. The plywood is 24 mm thick and 300 mm wide; the flanges are 50 mm × 100 mm (actual size). The modulus of elasticity for the plywood is 11 GPa and for the pine is 8 GPa. (a) If the allowable stresses are 14 MPa for the plywood and 12 MPa for the pine, find the allowable bending moment \(M_{\text{max}}\) when the beam is bent about the z axis. (b) Repeat part (a) if the beam is now bent about its y axis.