Flexural-torsional buckling of fiber-reinforced plastic composite open channel beams

A combined analytical and experimental study for flexural-torsional buckling of pultruded fiber-reinforced plastic (FRP) composite open channel beams is presented. Based on the second variational principle and nonlinear plate theory, the total potential energy of the channel beam including shear effect and beam bending-twisting coupling is derived. The stress resultants and displacement fields for flexural-torsional buckling of open channel beams under combined sideway flexural and torsional effects are given. The analytical eigenvalue solutions for cantilever open channel beams are obtained through the transcendental shape function. An experimental study of three different geometries of FRP cantilever open channel beams is performed, and the critical buckling loads for different span lengths are measured and compared with the analytical solutions and numerical finite element results. A parametric study is conducted to show the effects of load location, fiber orientation and fiber volume fraction on the buckling behavior, and it sheds light on optimal design of FRP channel beams for flexural-torsional buckling. The proposed analytical solutions can be used to predict the buckling loads of FRP channels, to formulate simplified design equations, and optimize efficient sections.