EFFECT OF BRIDGE BEARINGS ON VERTICAL POUNDING IN BRIDGES UNDER NEAR-FAULT VERTICAL EARTHQUAKES

A beam-spring-rod continuous body model was used to simulate vertical pounding in a two-span continuous beam bridge with bearings. The theoretical solutions for multiple vertical poundings were obtained by expanding the transient wave functions in a series of eigenfunctions and using the transient internal force method with the contact interfacial force of combined body, and the effect of bridge bearings on vertical pounding was then investigated. The research results show that the vertical pounding responses including the number of impacts, pounding force and displacements are greatly influenced by the local contact rigidity of the deck and piers, which varies with the rigidity of the bridge bearings. Vertical pounding energy can be absorbed by the bridge bearings and the basic characteristics of vertical pounding can be changed as well, such as sub-pounding frequency and displacement response frequency. As the vertical earthquake period approaches the natural vibration period of bridge, the deck jumps and intense vertical pounding will take place between deck and bearing. Because the rigidity of the bridge bearings can be adjusted to change the natural period of the bridge, it is worthwhile to consider their effects on reducing the destructive effects of vertical poundings and improving of the bridge ability to resist vertical earthquakes when designing the bridge bearings.