Effect of the actual distribution of applied stresses on global buckling of isotropic and transversely isotropic thin-walled members: theoretical analysis

Pultruded thin-walled profiles made of fiber-reinforced polymer (FRP) materials are gaining increasing interest in the construction industry as primary and secondary load-bearing members. Due to the low thickness of these profiles, their design is often governed by overall or local buckling. Members manufactured with the traditional pultrusion process can be considered transversely isotropic, with the plane of isotropy perpendicular to the fiber direction. This behavior, for the typical range of properties of commercial FRP materials, may imply a pronounced sensitivity of the stress regime to the actual distribution of applied stresses. This was shown in a previous work by the Authors generalizing the exact theory of thin-walled isotropic beams developed by Capurso in 1964. In this paper, the exact theory of thin-walled beams is used as a basis for the first-order flexural-torsional and lateral buckling analysis of isotropic and transversely isotropic structural members. The effect on the critical load (or moment) of the actual distribution of the applied compressive stresses is analyzed. A numerical example is presented for the I-section under axial compression.