1 EXPERIMENTAL AND ANALYTICAL EVALUATION OF LATERAL BUCKLING OF FRP COMPOSITE CANTILEVER I-BEAMS

Pultruded Fiber-reinforced plastic (FRP) shapes (beams and column) are thin-walled or moderately thick-walled open or closed sections consisting of assemblies of flat panels. Due to the high strength-to-stiffness ratio of composites and thin-walled sectional geometry of FRP shapes, buckling is the most likely mode of failure before material failure for FRP shapes. In this paper, a combined analytical and experimental approach is used to characterize the lateral buckling of pultruded FRP composite cantilever I-beams. An energy method based on nonlinear plate theory is developed, and it includes shear effects and bending-twisting coupling. Three types of buckling mode shape functions (exact transcendental function, polynomial function, and half simply-supported beam function), which all satisfy the cantilever beam boundary conditions, are used to derive the critical buckling loads, and the accuracy of these approximations are studied and discussed. The effects of tip-load position, fiber orientation and fiber volume fraction on the critical buckling loads are investigated. Four common FRP I-beams with different cross-sectional geometries and various span lengths are experimentally tested, and the critical buckling loads are measured. A good agreement among the proposed analytical method, experimental testing and finite-element modeling is observed, and simplified explicit equations for lateral buckling of cantilever I-beams with the applied load at the centroid of the cross-section are formulated. The proposed analytical solution can be used to predict the lateral buckling loads for FRP cantilever I-beams and to assist practitioners to perform buckling analyses of customized FRP shapes as well as to optimize innovative sections