Experimental and numerical investigations on pre-twisted steel box-section columns

Experimental and numerical investigations on pre-twisted steel box-section columns are presented in this paper. A series of tests was conducted to investigate the effects of pre-twisted angle ratio on the compressive behaviour of steel box-section columns. The pre-twisted angle ratios of 3 degrees/m and 15 degrees/m were considered in the design of column specimens. The column specimens had effective lengths of 1.5 m and 4.0 m, and cross-section dimensions of 280 x 100 (depth x width) mm and 350 x 120 mm. A non-linear finite element model (FEM) considering geometric imperfections was developed. The results from the finite element analysis were compared with those from the column tests in terms of ultimate loads, failure modes and load-deformation curves. After successful verification, the FEM was employed to conduct an extensive parametric study on the structural behaviour of pretwisted steel box-section columns. The key parameters in the parametric study included the pre-twisted angle ratios, ratios of depth to width in cross section, effective column lengths and end boundary conditions. It was shown that the pre-twisted angle ratios had little effect on the axial capacity, initial stiffness and lateral deformation capacity of shorter columns that failed by plastic yielding; however, more significant effects were found for the longer columns that failed by elastic flexural buckling. Theoretical analysis on the elastic buckling of pre-twisted steel box-section columns was conducted. Based on which, the formula for the buckling coefficient (reduction factor) was proposed that was suitable for the prediction of ultimate strength of pre-twisted steel box-section column.