Local buckling of composite FRP shapes by discrete plate analysis

An analytical study of local buckling of discrete laminated plates or panel s of fiber-reinforced plastic (FRP) structural shapes is presented. Flanges of pultruded FRP shapes are modeled as discrete panels subjected to unifor m axial in-plane lends. Two cases of composite plate analyses with differen t boundary conditions and elastic restraints on the unloaded edges are pres ented. 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 tec hnique and regression analysis, simplified expressions for predictions of p late buckling stress resultants are efficiently formulated in terms of coef ficients of boundary elastic restraints. The effects of restraint at the fl ange-web connection are considered, and explicit expressions for the coeffi cients of restraint for I- and box-sections are given; it is shown that act ual cases lie between simply supported and fully restrained (clamped) condi tions. The theoretical predictions show good agreement with experimental da ta and finite-element eigenvalue analyses for local buckling of FRP columns . In a similar manner, web plate elements of FRP shapes under in-plane shea r loads are modeled with and without elastic restraints provided by the fla nge panels. The present formulation can be applied to several cases to dete rmine local buckling capacities of laminated plates with elastic restraints along the unloaded edges and can be further used to predict the local buck ling strength of FRP shapes, such as columns and beams.