Keywords: thin-walled composite, classical lamination theory, lateral buckling.

Fiber-reinforced plastics (FRP) have been increasingly used over the past few decades in a variety of structures that require high ratio of stiffness and strength to weight. In the construction industry, recent applications have shown the structural and cost efficiency of FRP structural shapes, such as thin-walled open sections. The design of thin-walled members is governed by stability considerations due to their slenderness. Thin-walled open section members made of isotropic materials have been studied by many researchers. For isotropic materials, buckling by bending and torsion can separately occur under axial load if the cross section has two axes of symmetry. For composite laminates, however, the bending and torsion are no longer uncoupled even for a doubly-symmetric section, and flexural-torsional buckling should be considered. Little work have been done to address the lateral buckling of composite thin-walled members.

Bauld and Tzeng [1] extended Vlasov's thin-walled bar theory to symmetric fiber-reinforced laminates. Davalos and Qiao [2] presented a combined analytical and experimental evaluation of flexural-torsional and lateral-distorsional buckling of FRP composite wide-flange beams. Kabir and Sherbourne [3] studied the lateral buckling of thin-walled composite beams including shear effects, and local buckling effects. All the literature mentioned above dealt with the composite beams with symmetric stacking sequences. Recently, Lee and Kim [4] proposed an analytical model for buckling of axially-loaded wide-flange composite beams. A general configuration including unsymmetric lamination sequences, various boundary conditions, are considered in their model.

In the present study, the work by Lee and Kim [4] is extended to the lateral buckling of a wide flange composite subjected to transverse loads and end moments is developed. This model is based on the classical lamination theory, and accounts for the coupling of flexural and torsional modes for arbitrary laminate stacking sequence configuration, i.e. unsymmetric as well as symmetric, and various boundary conditions. A displacement-based one-dimensional finite element model is developed to predict critical loads and corresponding buckling modes for a thin-walled composite bar with arbitrary boundary conditions. Governing buckling equations are derived from the principle of the stationary value of total potential energy. Numerical results are obtained for laterally-loaded thin-walled composites with angle-ply and quasi-isotropic laminates. The effects of fiber angle, material anisotropy, and boundary conditions on the critical buckling loads and mode shapes are parametrically studied.

1

Bauld, N. R. and Tzeng, L. S., "A Vlasov theory for fiber-reinforced beams with thin-walled open cross section," International Journal of Solids and Structures, Vol.20, No. 3, 1984, pp.277-297. doi:10.1016/0020-7683(84)90039-8

2

Davalos, J. F. and Qiao, P., "Analytical and experimental study of lateral and distorsional buckling of FRP wide-flange beams," Journal of Composites for Construction, ASCE, November, 1997, pp.150-159. doi:10.1061/(ASCE)1090-0268(1997)1:4(150)

3

Kabir, M. Z. and Sherbourne, A. N., "Lateral-torsional buckling of post-local buckled fibrous composite beams", Journal of Engineering Mechanics, ASCE, July, 1998, pp.754-764. doi:10.1061/(ASCE)0733-9399(1998)124:7(754)

4

Lee, J. and Kim, S., "Flexural-torsional buckling of thin-walled I-section composites," Computers and Structures, Vol. 79, No. 10, 2001, pp. 987-995. doi:10.1016/S0045-7949(00)00195-4

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