Kalkan, İlker2025-01-212025-01-2120101308-5514https://dergipark.org.tr/tr/download/article-file/353300https://dergipark.org.tr/tr/pub/umagd/issue/31719/345714https://hdl.handle.net/20.500.12587/19872In this study, different versions of the Southwell plot method were applied on the lateral deflection, twisting rotation and load data of slender rectangular reinforced concrete beams, experiencing elastic lateral torsional buckling. Among different versions of the Southwell plot, the Modified (Trahair) Plots produced the critical load estimates in closest agreement with the experimental buckling loads of the beams. The initial geometric imperfection estimates closest to the actual values were obtained from the standard Southwell Plots. The analysis also indicated that the slope of the Southwell plot of a reinforced concrete beam does not change up to 80-90% of the critical load. In the vicinity of buckling and in the post-buckling stage of the test, cracking of concrete caused by the lateral bending and torsional moments in the beam results in the gradual decrease of the slope of the plot.eninfo:eu-repo/semantics/openAccessSouthwell PlotMassey PlotMeck PlotModified Trahair PlotLateral torsional bucklingLateral deflectionTwisting rotationModifications to the Southwell plotSlender reinforced concrete beamsArticle21-5866345714