Buckling and Postbuckling of Simply Supported Anisotropic Laminated Web Beams Characterized Using the Southwell Technique

This study investigates the lateral-torsional buckling behavior of ten glass fiber–reinforced plastic and carbon fiber–reinforced plastic thin-walled rectangular beams using numerical and experimental techniques with analytical verification. The beams were composed of various anisotropic laminated composite materials in different layups. They were loaded manually at mid-span with small load increments to assess their critical buckling and postbuckling state. The experimental results were analyzed using Riks analysis to understand the influence of material anisotropy and geometric parameters on the buckling and postbuckling response. A new Southwell formulation was also established to enhance the practical prediction of the critical buckling load compared to the actual numerical and classical analytical stability estimates. This Southwell method leverages the relationship between deflected angle and load to provide a more refined approach for better estimating linearized buckling in complex composite structures. The outcomes of this research contribute to understanding the buckling and postbuckling behavior of anisotropic laminated beams and offer novel simplified tools for engineers and researchers in designing composite structures. Overall, the limit loads obtained from actual numerical models, the Southwell method, and the classical analytical method show strong consistency with each other despite the missing limit load from the experimental response. Significant initial imperfections trigger the latter lack of limit loads.