고체역학 (Gere) — Axially Loaded Members: Problem 2.4-16

2.4-16 A rigid bar of weight \(W = 800\text{ N}\) hangs from three equally spaced vertical wires (length \(L = 150\text{ mm}\), spacing \(a = 50\text{ mm}\)): two of steel and one of aluminum. The wires also support a load \(P\) acting on the bar. The diameter of the steel wires is \(d_s = 2\text{ mm}\), and the diameter of the aluminum wire is \(d_a = 4\text{ mm}\). Assume \(E_s = 210\text{ GPa}\) and \(E_a = 70\text{ GPa}\). (a) What load \(P_{\text{allow}}\) can be supported at the midpoint of the bar (\(x = a\)) if the allowable stress in the steel wires is \(220\text{ MPa}\) and in the aluminum wire is \(80\text{ MPa}\)? (See figure part a.) (b) What is \(P_{\text{allow}}\) if the load is positioned at \(x = a/2\)? (See figure part a.) (c) Repeat part (b) if the second and third wires are switched as shown in the figure part b.