Buckling strength and ductility evaluation of thin-walled steel stiffened square box columns with uniform and graded thickness under cyclic loading

Abstract

Thin-walled steel stiffened square box columns are becoming an increasingly attractive choice as cantilever bridge piers due to their architectural, structural and constructional advantages. This paper investigates the behavior of thin-walled steel columns with uniform square box sections (B) and newly proposed graded-thickness square box sections (GB) under constant axial and cyclic lateral loading. The analysis is carried out using a finite-element model (FEM) which takes into account the effect of both material and geometric nonlinearities. First, the accuracy of the employed FEM is verified based on the experimental results. Then, a GB column with size and volume of material equivalent to a B column is introduced. The proposed GB column is proved to have significant improvements in strength, ductility, and post-buckling behavior as compared to its counterpart B column. As a part of this research, a comprehensive parametric study is carried out to investigate the effects of main key parameters including: the width-to-thickness ratio parameter (Rf), the column slenderness ratio parameter (λ), the magnitude of axial load (P/Py), and the number of loading cycles (N) on the strength and ductility of the B and GB columns. Finally, a series of proposed formulae for strength and ductility evaluation of the B and GB columns is given.