고체역학 (Gere) — Stresses in Beams (Basic Topics): Problem 5.6-9

5.6-9 A floor system in a small building consists of wood planks supported by 50 mm (nominal width) joists spaced at distance \( s \) and measured from center to center (see figure). The span length \( L \) of each joist is 3 m, the spacing \( s \) of the joists is 400 mm, and the allowable bending stress in the wood is 8 MPa. The uniform floor load is \( 6 \text{ kN/m}^2 \), which includes an allowance for the weight of the floor system itself. (a) Calculate the required section modulus \( S \) for the joists, and then select a suitable joist size (surfaced lumber) from Appendix G, assuming that each joist may be represented as a simple beam carrying a uniform load. (b) What is the maximum floor load that can be applied to your final beam selection in part (a)?