Local Buckling of Thin- and Thick-Walled Open Sections Using an Enhanced Mindlin–Reissner Finite Strip with Drilling Degree of Freedom

This study enhances the finite strip method (FSM) based on Mindlin–Reissner theory by incorporating a drilling degree of freedom derived from continuum mechanics’ true rotation. The stiffness matrix for a three-nodal-line finite strip is explicitly formulated in closed form, incorporating this sixth degree of freedom. Additionally, the geometric stiffness matrix is derived, accounting for stress variations across the width and thickness. The proposed finite strip enables local buckling analysis and facilitates the classification of thin- and thick-walled members with open sections, such as channel and I-sections, based on the width-to-thickness ratio.