Numerical investigation of the dynamic behavior of long-span CFST arch bridge under combined pulse-type ground motions and hanger fracture

This study examines the effects of pulse-type ground motions and hanger fracture on concrete-filled steel tube (CFST) arch bridges, particularly the nonlinear effects of the combination of the two which only consider structural geometric nonlinearity. A “decomposition-superposition” method is used to artificially synthesize pulse-type ground motions, and the equivalent unloading method based on the construction demolition approach is applied to hanger fracture simulation. The effects of pulse parameters and hanger fracture are measured in terms of arch ribs stress and displacement, girders moment and displacement, and hanger force. Moreover, the combined effects of pulse-type ground motions and hanger fracture on the responses are assessed for the variation between only hanger fracture and combined condition. The results show that the dynamic responses of the arch bridge significantly increase with the amplitude values of the pulse. Resonance effects are observed near the structure's natural vibration period. Bidirectional pulses generate larger responses in the arch bridge than unidirectional pulses. The dynamic responses of the main girder and stress in the arch ribs are strongly affected by the fracture location and the number of hanger fractures. The redistribution ratio of hanger forces decreases with increasing distance from the rupture zone and increasing hanger length but increases with the number of fracture hangers. Near-fault pulse ground motions exacerbate the effects of hanger fracture and alter the force redistribution mechanism. Compared with hanger fracture alone, dynamic coupling increases the residual hanger forces by 25–53 %, with the maximum increment occurring at the 1/4 position of the arch rib. The addition of pulse-type ground motions under hanger fracture changes the original response pattern of the arch bridge to hanger fracture. Therefore, the combined effects of pulse-type ground motions and hanger fractures should be considered in the CFST bridges seismic design.