Extremely Low-Cycle Fatigue Tests of Thick-Walled Steel Bridge Piers

To study extremely low-cycle fatigue performance of steel bridge structures, a total of nine steel bridge piers with unstiffened thick-walled box sections were tested in this study. The effects of various parameters, including cross-sectional shape (with or without an extension part), loading pattern, and width-thickness and slenderness ratios were investigated. Experimental results demonstrate that ductile cracks occurred at the column base in all specimens regardless of cyclic-loading histories and that ductile crack initiation life is sensitive to loading pattern, cross-sectional shape, and the width-thickness ratio. In all tests, the ductile crack began in the pier-to-base weld, and subsequent cyclic loads resulted in the ductile cracks growing at the weld toes along web and flange directions and then propagating into the base metal, which triggered an obvious decrease in strength capacity. A significant delay was observed between ductile crack initiation and maximum strength capacity. Moreover, ductile crack initiation and propagation may be accompanied by local buckling.