Seismic Analysis Model of Partially Concrete-Filled Steel Piers Considering Ultralow-Cycle Fatigue Crack Propagation

Seismic performance of partially concrete-filled steel tube (PCFST) bridge piers is controlled by the coupled failure of ultralow-cycle fatigue (ULCF) and local instability of steel plates. An empirical formula was established for the plastic fracture displacement on average stress triaxiality of the crack intiation process, and the two-stage prediction model for the ULCF cracking of steel was improved. Furthermore, an empirical formula was established for the plastic strain amplification factor on the element size and the stress triaxiality of the coarse model. A complete modeling method was proposed for the seismic performance analysis model of PCFST piers considering ULCF cracking.