Ductile crack initiation and propagation in steel bridge piers subjected to random cyclic loading

Results from five cyclic tests of steel bridge piers are presented to examine the extremely low-cycle fatigue (ELCF) behavior of steel bridge piers under random cyclic loading. It is observed that using test results of constant cyclic loading to predict the ELCF behavior under random loading may be not effective. In this study, the random cyclic loading patterns are determined using dynamic analytical results. The effect of various parameters, including axial force ratio, earthquake ground motion type and repeated earthquakes, is investigated. The dynamic analysis suggests that all of these parameters are shown to have a large influence on ELCF behavior of structures. The test data reveal that the sudden increase or decrease displacement amplitude has a significant effect on the ELCF behavior, including the ductile crack initiation, propagation and final failure. Meanwhile, a four staged failure criterion is presented and effectively employed to investigate the ductile fracture of steel bridge piers with thick-walled box section.