고체역학 (Gere) — Axially Loaded Members: Problem 2.5-24

2.5-24 A rigid steel plate is supported by three posts of high-strength concrete each having an effective cross-sectional area \(A = 40,000 \text{ mm}^2\) and length \(L = 2 \text{ m}\) (see figure). Before the load \(P\) is applied, the middle post is shorter than the others by an amount \(s = 1.0 \text{ mm}\). Determine the maximum allowable load \(P_{\text{allow}}\) if the allowable compressive stress in the concrete is \(\sigma_{\text{allow}} = 20 \text{ MPa}\). (Use \(E = 30 \text{ GPa}\) for concrete.)