Modifications of standard GFRP sections shape and proportions for improved stiffness and lateral-torsional stability

In this paper the results of a comprehensive numerical investigation regarding the axial–flexural–torsional response of pultruded slender beams is presented. The goal is to propose GFRP standard cross-sections of such proportions and shapes that would possess improved strength, stability and deformational characteristics compared to the corresponding existing sections whose proportions are generally based on standard steel sections. As GFRP sections are thin-walled but are significantly less stiff than similar steel sections, the study focuses on enhancing their appropriate stiffness and buckling strength. The novel and efficient numerical model used in this investigation was developed by the writers and can be used to trace the complete pre-buckling geometrically nonlinear response of any GFRP or steel thin-walled member with open or closed cross-section. The bucking load is computed by the asymptotic value of the load–displacement curve. Members with I-, L-, T- and box sections are analyzed, considering different loading and boundary conditions. It is demonstrated that due to their unsuitable proportions, available standard GFRP sections do not have adequate stiffness and buckling strength. Consequently, recommendations are made for new sectional proportions and modified shapes, and some graphical results are presented to demonstrate how the results of the proposed method could be utilized in practical design situations. The superiority of the proposed sections is quantified by an efficiency factor, defined in terms of ratio of strength gain to material volume increase.