Effect of width–thickness ratio on capacity of pultruded square hollow polymer columns

Width–thickness ratio is an important geometric parameter in the local buckling of plates and, therefore, also for columns with square hollow sections (SHS). This paper reports on an investigation into the effects of width–thickness ratio (b/t) on the failure modes and load-carrying capacities of SHS columns made from pultruded glass fibre reinforced polymer (PFRP). Two SHS columns, with b/t = 10·7 or 15·9 were examined under axial compression. The experimental results revealed that local buckling occurred in the 15·9 section but not in the 10·7 section. From a theoretical analysis, a formulation of critical width–thickness values was established at the boundaries between failure modes of the columns under compression, considering the different boundary conditions of the side plates. It is commonly understood that global buckling occurs in columns with higher non-dimensional slenderness. This is only true when the width–thickness ratio is less than the derived critical value. The experimental results from this study and previous works are consistent with the developed theoretical estimations of the failure modes and load-carrying capacities for PFRP SHS columns, considering the effects of both non-dimensional slenderness and width–thickness ratio.