Dynamic behaviors of bridges considering pounding and friction effects under seismic excitations

Dynamic responses of a bridge system with several simple spans under longitudinal seismic excitations are examined. The bridge system is modeled as the multiple oscillators and each oscillator is consisting of four degrees-of-freedom system to implement the poundings between the adjacent oscillators and frictions at movable supports. Pounding effects are considered by introducing the impact elements and a bi-linear model is adopted for the friction force. From the parametric studies, the pounding effects are found to induce the more complicated seismic responses of the multi-simple span bridge and to restrain significantly the relative displacement between the adjacent vibration units with the dissimilar vibration frequencies. The smaller gap size restricts the relative displacement more tightly due to more frequent poundings. The frictions at the movable supports also reduce the seismic responses significantly when the seismic excitation Is moderate. It is found that the relative displacement between the vibration units with abutment and the adjacent unit with pier becomes much larger than the response between the pier units. Therefore, the unseating failure probability of the girders spanning between the abutment and pier is assumed to be much higher than the case of the pier to pier.