Local buckling of composite FRP shapes by discrete plate analysis

An analytical study of local buckling of discrete laminated plates or panels of fiber-reinforced plastic (FRP) structural shapes is presented. Flanges of pultruded FRP shapes are modeled as discrete panels subjected to uniform axial in-plane lends. Two cases of composite plate analyses with different boundary conditions and elastic restraints on the unloaded edges are presented. By solving two transcendental equations simultaneously, the critical buckling stress resultant and the critical value of the number of buckled waves over the plate aspect ratio are obtained. Using this new solution technique and regression analysis, simplified expressions for predictions of plate buckling stress resultants are efficiently formulated in terms of coefficients of boundary elastic restraints. The effects of restraint at the flange-web connection are considered, and explicit expressions for the coefficients of restraint for I- and box-sections are given; it is shown that actual cases lie between simply supported and fully restrained (clamped) conditions. The theoretical predictions show good agreement with experimental data and finite-element eigenvalue analyses for local buckling of FRP columns. In a similar manner, web plate elements of FRP shapes under in-plane shear loads are modeled with and without elastic restraints provided by the flange panels. The present formulation can be applied to several cases to determine local buckling capacities of laminated plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes, such as columns and beams.