Commonly used isolation bearings include laminated rubber bearings, lead core rubber bearings and friction pendulum bearings, etc. Rubber bearings have stable performance, good durability and wide application. However, the vertical bearing capacity of rubber bearings is relatively low, and their energy dissipation capacity is limited. Later, a variety of high-performance isolation bearings were successively developed, such as high-damping rubber bearings, friction sliding type bearings, spherical bearings, high-load-bearing multi-directional rotating bearings and friction sliding isolation systems, etc.
The displacement of the isolation structure is concentrated in the isolation layer. To limit excessive displacement, rubber bearings are usually combined with dampers to achieve the purpose of reducing the seismic response of the superstructure and the displacement between isolation layers.
For isolation systems that use liquid viscous dampers to constrain horizontal displacements, the practical functionality and reliability of the dampers are of vital importance:
(1) Adding viscous dampers can reduce the final horizontal displacement of the structure compared with a simple isolation system.
(2) After the addition of dampers, the damping ratio of the main structure increases, reducing its seismic load.
(3) The use of viscous dampers that can work well at different temperatures and frequencies is a good supplement to rubber isolation bearings that have some deficiencies in working performance under different environments. It can greatly enhance the reliability of the entire system.
(4) Prevent the isolation pad from breaking or collapsing and becoming unstable. Rubber pads are prone to instability and damage when the height is too high. When dampers are added to restrict the movement displacement, the possibility of such instability and damage can be greatly reduced.
(5) The combined use of isolation bearings and viscous dampers can reduce the cost spent to achieve the purpose of vibration reduction. To achieve the goal of further reducing the horizontal displacement and seismic load of the structure by 50%, the cost of adding rubber pads is much greater than the additional cost after installing dampers.