Compressive Strength of Rocking Steel Bridge Pier upon Rocking

Controlled-rocking piers have gained popularity over the last few decades to achieve enhanced seismic performance for bridge structures. Past research on this system has focused on concrete rocking bridge piers. Recently, rocking bridge piers made from tubular steel sections have been proposed as a possible cost-effective alternative to concrete piers. A steel rocking bridge pier comprises a circular steel tube with welded circular plates at the top and bottom ends, post-tensioned tendons, and energy dissipaters at the rocking interface(s). During a seismic event, lateral displacement of the bridge superstructure is accommodated by means of gap opening and closing at the rocking interfaces located at the top and bottom ends of the columns. Upon column rocking, the gravity load is no longer evenly distributed over the column cross-section, which induces stress concentration and flexural demand on the column that can detrimentally affect its compressive resistance. This article presents a numerical investigation using three-dimensional continuum finite element analysis that was performed to evaluate the effect of column rocking on the compressive resistance of tubular steel bridge piers. The influence of key parameters is examined, including the column diameter-to-thickness ratio, the thickness and overhang dimension of the end plates, the axial load ratio, and the tilt angle of the column. For the range of values considered for those parameters, the study shows that the loss in compressive resistance compared to a vertical column can vary from 13 to 58%, and the most influential parameter is the column diameter-to-thickness ratio.