Dynamic behavior of a simply supported bridge with a switching crack subjected to seismic excitations and moving trains

• The change in the equilibrium position of the bridge is considered during the vibration analysis.
• An added vibrational displacement appears due to the crack switching.
• The equilibrium position is shifted down by a train, and the switching effect is reduced.

This paper presents a numerical solution for the dynamic response of a simply supported bridge with a switching crack subjected to seismic excitations and moving trains. The train vehicle is represented by a four degrees-of-freedom model, and the seismic excitation is exerted using the acceleration input. While the crack state remains constant, the bridge vibration is evaluated through a modal analysis. When the crack is switching, the equilibrium position is taken into account to analyze the change of the displacement components. The proposed method is used to study the response characteristics of a numerical bridge, and the results show that under the independent action of seismic load, the equilibrium position changes suddenly at the switching instant and an added vibrational displacement appears. Finally the vibrational displacement is increased by the crack switching and the vibration amplitude becomes larger. Under the combined action of the seismic excitation and the train, the equilibrium position is shifted down, and the effect of the added displacement is reduced. So the vibration amplitude is smaller under the combined action than under the independent action. Meanwhile, the amplitude also is affected by the train weight and velocity.