How do bridge bearings affect the seismic performance of bridges?

The bridge bearings are developed based on the specifications of JT/T4-2019, JT/T663-2019, JT/T391-2009, GB/T17955-2009, and JTG D62-2019 for the design of reinforced concrete and prestressed concrete bridges and culverts for highway bridges, using dynamic analysis.

Bridge bearings directly determine the seismic performance of bridges through two paths: stiffness regulation and energy dissipation. Their role can be summarized into four points: stiffness adjustment - determining the natural vibration period of the structure. The lower the horizontal stiffness of the bearings, the longer the longitudinal period of the bridge, which can avoid the dominant frequency band of earthquakes and significantly reduce the peak seismic force. Taking a continuous beam bridge as an example, after replacing single fixed bearings with double fixed bearings, the longitudinal period is shortened by 27.7%, and the seismic shear force increases by 33.5% instead. Friction energy dissipation - ordinary sliding bearings rely on interface friction energy dissipation to reduce the bending moment at the bottom of the pier by 12% -14%; Lead rubber bearings, friction pendulum bearings and other seismic isolation devices can further reduce longitudinal shear force and bending moment by 30% -35% through hysteresis energy dissipation, while controlling displacement within a recoverable range.

Changes in the arrangement of displacement and internal force redistribution bearings will significantly alter the distribution of seismic forces: in continuous beam bridges, the more fixed bearings there are, the greater the internal forces in the middle pier columns; On the contrary, multi-point active supports can disperse longitudinal forces to both sides and reduce the peak value of a single pier. The coupling effect of pier height and pier height jointly determine the flexibility of the structure. When the pier height increases, the overall stiffness of the support pier column decreases, and the seismic force decreases and tends to stabilize; However, the peak shaving effect varies with the height of the pier depending on the type of support: under high pier conditions, the reduction amplitude of bending moment by seismic isolation bearings still remains above 25%. Therefore, reasonable selection (plate type → basin type → seismic isolation) and optimized layout (fixed/movable ratio, pier height coordination) are key technical measures to improve the seismic performance of bridges.