Performance of Thin-Walled Steel Tubular Circular Columns with Graded Thickness under Bidirectional Cyclic Loading

Thin-walled steel tubular circular columns are an attractive choice for elevated highway bridge piers due to both their structural advantages, and ease and speed of construction. However, local buckling, global buckling, or a combination of both are considered a main reason for a significant loss of strength and ductility in these columns, or possibly a full collapse under severe earthquakes. This paper investigates the hysteretic behavior of circular thin-walled steel columns with uniform and graded thickness under constant axial and bidirectional cyclic lateral loading. The paper's analysis is carried out using a finite-element model (FEM) which considers both material and geometric nonlinearity. The accuracy of the employed FEM is validated based on experimental results. Then, five different configurations of graded-thickness thin-walled columns with the size and volume of material equivalent to a uniform column are investigated. The graded-thickness columns are found to make significant improvements in ultimate strength, ductility, and post-buckling behavior as compared to their counterpart uniform column, emphasizing the sectional configuration in the graded-thickness columns.