고체역학 (Beer) — Pure Bending: Problem 4.190

4.190 Show that if the cross section of a curved beam consists of two or more rectangles, the radius \( R \) of the neutral surface can be expressed as \[ R = \frac{A}{\ln \left[ \left( \frac{r_2}{r_1} \right)^{b_1} \left( \frac{r_3}{r_2} \right)^{b_2} \left( \frac{r_4}{r_3} \right)^{b_3} \cdots \right]} \] where \( A \) is the total area of the cross section.