Ultimate State of Thin-Walled Circular Steel Columns Subjected to Biaxial Horizontal Forces and Biaxial Bending Moments Caused by Bidirectional Seismic Accelerations

Abstract

To check the safety of thin-walled circular steel columns used for bridge piers of elevated-girder bridges, a versatile interaction equation is derived to specify the ultimate state of the columns under the coupling of bidirectional horizontal seismic accelerations. These bidirectional seismic accelerations generally cause biaxial horizontal force components and biaxial bending moment components to act at the top of the columns. Therefore, the interaction equation is derived in this paper in terms of these force and moment components. In this interaction equation, the bending moment components are converted to equivalent horizontal force components. The accuracy of the ultimate interaction equation is first investigated by carrying out a bidirectional shaking table test and an advanced dynamic analysis on single-column models in which a mass with translational and rotational inertias is fixed at the top of the columns. As an application to actual problems, an advanced dynamic response analysis is used to examine the validity of the interaction equation when applied to a column of a two-span simply supported elevated-girder bridge model under bidirectional seismic accelerations. In this model, the center of a superstructure is supported by a single circular steel column, whereas both ends of the superstructure are supported by abutments. The numerical analysis showed that the proposed ultimate interaction equation considering the effects of the biaxial horizontal force components and biaxial bending moment components accurately predicts the ultimate state of the column. The biaxial bending moment components have some large effect on the ultimate state of the column.