Flange local buckling of pultruded GFRP box beams

An experimental program investigating the flange local buckling (FLB) behavior of pGFRP box-sections is reported. The commonly accepted design equation based on plate theory was validated although importance of accurate assessment of the rotational stiffness of the web-flange junctions was identified. It is concluded that the lower bound solution, assuming the flange is a simply-supported plate subject to uniform compressive stress, results in uniformly conservative predictions of the critical FLB moments. The theoretical solution accounting for flange plate edge support stiffness based only on web stiffness, material and geometric properties of the cross section over predicts the support stiffness resulting in unconservative predictions of FLB behavior. The rotational stiffness of flange-web junction of the pGFRP box-section is also investigated experimentally. It is found that the actual rotational stiffness of flange-web junction is relatively low, closer to the simply-supported boundary condition. The role of fiber architecture at the web-flange junction is identified as affecting this behavior. The conclusions of this study support the use of the lower bound solution for design of pGFRP box-sections.