Large displacement isolation bearing
The disclosed seismic isolation bearing includes an upper base plate, a lower base plate, a disc bearing core, and a shear spring surrounding the disc bearing core. Concave recesses are formed in a lower surface of the upper base plate and an upper surface of the lower base plate. The disc bearing core is centrally positioned with respect to the planes of the upper and lower base plates and can slide along the recesses of the upper and lower base plates, where the recesses exert a lateral return force on the disc bearing core when displaced from a central position. The shear spring surrounds the disc bearing core, deforms in shear upon lateral movement of the upper base plate relative to the lower base plate, and exerts a lateral return force on the upper base plate when the upper base plate is laterally displaced.
1. A seismic isolation bearing comprising:
an upper base plate having an upper surface and a lower surface, the lower surface of the upper base plate having a concave recess formed therein;
a lower base plate having an upper surface and a lower surface, the upper surface of the lower base plate having a concave recess formed therein;
a disc bearing core centrally positioned with respect to the planes of the upper base plate and lower base plate, the disc bearing core being in contact with the recess of the upper base plate and the recess of the lower base plate, and configured to slide along the recess of the upper base plate and to slide along the recess of the lower base plate, the recesses exerting a lateral return force on the disc bearing core when displaced from a central position; and
a shear spring surrounding the disc bearing core, the shear spring (i) being coupled to the lower surface of the upper base plate and the upper surface of the lower base plate, and being configured to deform in shear upon lateral movement of the upper base plate relative to the lower base plate, and to exert a lateral return force on the upper base plate when the upper base plate is laterally displaced, and (ii) including alternating layers of an elastomeric material and a substrate material, the shear spring being configured to deform in shear along the layers of elastomeric material, and each layer of elastomeric material having a shape factor that does not exceed a value of 1.
2. A seismic isolation bearing as in claim 1 wherein a height of each layer of substrate material is smaller than the height of each layer of elastomeric material to provide added damping.
3. A seismic isolation bearing as in claim 1 wherein the elastomeric material is rubber and the substrate material is steel.
4. A seismic isolation bearing as in claim 1 wherein the layers of substrate material are configured to yield upon lateral deflection of the at least one shear spring to provide added damping.
5. A seismic isolation bearing as in claim 1 wherein the layers of substrate material are made of another elastomeric material that is stiffer than the layers of elastomeric material.
6. A seismic isolation bearing as in claim 1 wherein the shear spring includes an upper mounting plate configured to be attached to the lower surface of the upper base plate, and includes a lower mounting plate configured to be attached to the upper surface of the lower base plate.
7. A seismic isolation bearing as in claim 1 wherein the disc bearing core is configured to support all of a load on the seismic isolation bearing, and the shear spring is configured to not support any of the load on the seismic isolation bearing.
8. A seismic isolation bearing as in claim 1 wherein the shear spring is configured to support less than one third of a total load on the seismic isolation bearing.
9. A seismic isolation bearing as in claim 1 wherein a depth-to-diameter ratio of the recess of the lower base plate is less than 0.01.
10. A seismic isolation bearing as in claim 9 wherein a depth-to-diameter ratio of the recess of the upper base plate is less than 0.01.
11. A seismic isolation bearing as in claim 1 wherein the disc bearing core includes:
an upper disc bearing plate;
a lower disc bearing plate; and
an elastomeric disc pad coupled between the upper disc bearing plate and the lower disc bearing plate.
12. A seismic isolation bearing as in claim 1 wherein the upper base plate includes an upper support plate and an upper dish plate, an upper surface of the upper dish plate being coupled to a lower surface of the upper support plate, and the recess of the upper base plate being formed in the lower surface of the upper dish plate.
13. A seismic isolation bearing as in claim 12 wherein the shear spring is coupled to the lower surface of the upper support plate and surrounds the upper dish plate.
14. A seismic isolation bearing as in claim 1 wherein the lower base plate includes a lower support plate and an lower dish plate, a lower surface of the lower dish plate being coupled to an upper surface of the lower support plate, and the recess of the lower base plate being formed in the upper surface of the lower dish plate.
15. A seismic isolation bearing as in claim 14 wherein the shear spring is coupled to the upper surface of the lower support plate and surrounds the lower dish plate.
16. A seismic isolation bearing as in claim 1 wherein the disc bearing core includes a shear pin at the center of the disc bearing core to prevent shearing of the disc bearing core.
17. A seismic isolation bearing as in claim 1 wherein the disc bearing core does not include a shear pin.