Ductility of steel short cylinders in compression and bending

During the Hyogoken-Nanbu earthquake near Kobe, Japan, on January 17, 1995, damage occurred not only in steel box-section bridge piers but also in pipe-section piers. The pipe-section piers are usually designed with relatively large radius-thickness ratios, which make them susceptible to damage by local buckling during a severe earthquake event. To evaluate the damage of such columns, the ductility capacity of steel short cylinders is needed. For this purpose, an elastoplastic large deformation analysis of pipe-section stub-columns is carried out, In the analysis, a type of four-node doubly curved shell element is employed. Both the initial geometrical deflection and the residual stresses are taken into consideration. An elastoplastic strain hardening model is adopted to consider the material nonlinearity, Numerical results are then compared with previous test results and analytical results. In addition, a parametric study is conducted to investigate the effects of various parameters such as the length-diameter ratio, radius-thickness ratio, and axial load on the ultimate strength and ductility of the cylinders. Finally, design formulas for the ultimate strength and ductility of the cylinders in compression and in combined compression and bending are proposed.