LATERAL-TORSIONAL BUCKLING OF A PULTRUDED I-BEAM

Measured short-term critical loading for linear elastic lateral-torsional buckling of a pultruded I-beam has been compared with theoretical predictions. In the buckling experiment, an E-glass reinforced polymer I-beam was simply supported about the major axis, and supported at both ends such that lateral deflection, warping and twist were restrained. It was subjected to a central point load applied to the top compression flange. The experimental evidence for critical loading is shown to compare favourably with the predictions using a finite difference method. The finite difference approach is used to solve the governing differential equation derived using thin-walled theory. Through the finite difference and other analytical models, it is shown that the classical one-dimensional isotropic theories can be adapted, by suitable substitution for the moduli parameters, to predict the buckling load for composite beams made from orthotropic panels. For the case where the load is applied at the centroid of the I-section, the design procedure given in an American design manual is shown to be conservative, providing the assumed boundary conditions at the supports are met.