Bridges, Tunnels and other Transportation Structures
Thin-walled steel tubular circular columns are widely used as cantilever bridge piers due to their excellent structural and constructional advantages. However, local buckling, global buckling or the interaction between both is usually the main reason for a significant loss of strength and ductility of thin-walled steel tubular circular columns, which eventually leads to their collapse under severe earthquakes. This paper investigates the behavior of thin-walled steel tubular circular columns with conventional uniform circular sections (C) and newly proposed graded-thickness circular sections (GC) under combined constant axial and biaxial cyclic lateral loading. The analysis is carried out using a finite-element model (FEM) which considers both material and geometric nonlinearities. First, the accuracy of the employed FEM is validated based on experimental results. Then, a GC column with size and volume of material equivalent to a C column is introduced. The proposed GC column is proved to have significant improvements in strength, ductility, and post-buckling behavior as compared to its counterpart C column. Additionally, an extensive parametric study is carried out to investigate the effects of main key design parameters including: the radius-to-thickness ratio (Rt), the column slenderness ratio (λ), the magnitude of axial load (P/Py), and the number of loading cycles (N) on the strength and ductility of the C and GC columns. Finally, seismic design formulae for strength and ductility evaluation of the C and GC columns are proposed.