고체역학 (Gere) — Stresses in Beams (Basic Topics): Problem 5.5-7

5.5-7 Each girder of the lift bridge (see figure) is 50 m long and simply supported at the ends. The design load for each girder is a uniform load of intensity 18 kN/m. The girders are fabricated by welding three steel plates to form an I-shaped cross section (see figure) having section modulus \( S = 46,000 \text{ cm}^3 \). What is the maximum bending stress \( \sigma_{max} \) in a girder due to the uniform load?