고체역학 (Beer) — Pure Bending: Problem 4.75

4.75 and 4.76 A beam of the cross section shown is made of a steel that is assumed to be elastoplastic with \(E = 29 \times 10^6 \text{ psi}\) and \(\sigma_Y = 42 \text{ ksi}\). For bending about the z axis, determine the bending moment at which (a) yield first occurs, (b) the plastic zones at the top and bottom of the bar are 1 in. thick.