1 EXPERIMENTAL AND ANALYTICAL EVALUATION OF LATERAL BUCKLING OF FRP COMPOSITE CANTILEVER I-BEAMS Pizhong Qiao and Guiping Zou, The University of Akron, Akron, OH Julio F. Davalos, West Virginia University, Morgantown, WV Abstract 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. Keywords: FRP Structural Shapes; Lateral Buckling; Cantilever Beams. Introduction Fiber-reinforced plastic (FRP) structural shapes (beams and columns) have shown to provide efficient and economical applications for civil engineering construction (e.g., in bridges, piers, retaining walls, airport facilities, storage structures exposed to salts and chemicals, and others). Most FRP shapes are thin-walled structures and manufactured by the pultrusion process. The material constituents for low-cost pultruded FRP shapes commonly consist of high-strength E-glass fiber and vinylester or polyester polymer resins, and due to this choice of materials, the structures usually exhibit relatively large deformations and tend to buckle globally or locally. Consequently, buckling is the most likely mode of failure before the ultimate load reaches the material failure [1-4]. A long slender beam under bending about the strong axis may buckle by a combined twisting and lateral (sideways) bending of the cross section. This phenomenon is known as lateral buckling, and an extensive review of analytical and theoretical investigations for steel and FRP composite beams has been presented in [5]. In this paper, a combined analytical and experimental study on lateral buckling of FRP cantilever I-beams is presented, and simplified equations for lateral buckling analysis are developed. Three different types of shape functions (exact transcendental function, polynomial