고체역학 (Beer) — Pure Bending: Problem 4.160

4.160 (a) Show that, if a vertical force P is applied at point A of the section shown, the equation of the neutral axis BD is \[ \left( \frac{x_A}{r_z^2} \right) x + \left( \frac{z_A}{r_x^2} \right) z = -1 \] where \(r_z\) and \(r_x\) denote the radius of gyration of the cross section with respect to the \(z\) axis and the \(x\) axis, respectively. (b) Further show that, if a vertical force Q is applied at any point located on line BD, the stress at point A will be zero.