" by Wai-Fah Chen and E.M. Lui, the textbook itself contains .
Chen often expresses answers in terms of effective length $K$. $P_cr = \frac\pi^2 EI(KL)^2$. $\frac\pi^2(KL)^2 = \frac20.19L^2 \Rightarrow KL = \frac\pi\sqrt20.19 \approx \frac3.144.49 \approx 0.699$. Result: $K \approx 0.7$. Structural Stability Chen Solution Manual
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