“…lateral deflection (δ) and rotation (φ), have been separately applied to determine critical loads through extrapolation techniques. Cheng and Yura [14] and Gregory [15,16], for instance, conducted experiments on lateral-torsional buckling of beams, and successfully determined the critical buckling condition by assuming that the Southwell Plot would be valid, separately, for both lateral deflection (δ) and rotation (φ). They made plots of δ/M (or δ/P) against δ, and φ/M (or φ/P) against φ.…”