Field of the Invention

The present invention relates, generally, to isolation bearings for use in supporting buildings, bridges, and other structures and, more particularly, to seismic isolation bearings having a restoring capability useful in the context of earthquakes and other seismic activity. Background of the Invention

Seismic isolation bearings, sometimes referred to as seismic base isolators, are generally well known. Seismic isolation bearings generally perform at least two principle functions, namely, decoupling and restoring.

Decoupling may be generally characterized as motion isolation, and involves at least partially isolating the structures supported by the bearing from the movement of the earth upon which the structure is supportec'. Typically, the decoupling function of an isolation bearing is effected by the use of a rubber element configured to deflect in response to seismic activity. However, the period, size, and bearing capacity of an isolation bearing is limited by the buckling and rollover capacity of the rubber. Practical rubber bearings typically exhibit periods on the order of two seconds, and exhibit a sheer strain (the ration of sheer displacement to rubber height) on the order of fifty percent (50%). In addition, typical rubber bearings exhibit bearing capacities in the range of 1,000 psi (pound/inch). These parameters, however, are often insufficient for use within the "near fault" zone, i.e., within fifteen miles from an active seismic fault. In addition, presently known rubber bearings are configured to accommodate only on the order of 0.02 radian bearing rotation.

Bearing recentering (restoring) mechanisms may comprise yield pins or other spring mechanisms for returning a bearing to its original, nominal position following an applied lateral force. See, for example, PCT application number PCT/94/13598, entitled Seismic Isolation Bearing, filed November 25, 1994 by the same inventor.

More recently, friction slides or bearings have been proposed to expand the foregoing parameters to accommodate periods on the order of four seconds and bearing

pressure capacities in the range of 3,500 psi. Such friction slider bearings often include teflon-lined steel plates within the bearing assembly, and are known to accommodate on the order of two to six feet of lateral displacement, which is often required for structures located at "near fault" installations. However, teflon bearings generally require a rubber plate bed to accommodate bearing rotation. Moreover, sliding bearings typically do not include a restoring mechanism and, thus, tend to displace in only one direction. In addition, the use of the aforementioned rubber plate dramatically reduces bearing capacity, for example to around 1 ,000 psi.

These are some prior patents related to friction or other bearings: U.S. Patent No. 4,644,714 issued February 24, 1987 to Zayas discloses a friction pendulum bearing, employing a polymer-matrix coated friction surface. U.S. Patent No. 4,726,161 issued February 23, 1988 to Yaghoubian discloses a rolling bearing utilizing a spring loaded telescoping mass with a housed, lubricated ball bearing cooperating with a spherical dish. However, due to the limited size of such bearings and the need for maintenance, their use is limited to museum object isolation. A seismic isolation bearing assembly is thus needed which overcomes the shortcomings of the prior art.

Summary of the Invention The present invention provides a seismic isolation bearing system which employs, in accordance with one aspect of the invention, ε spherical ball disposed between upper and lower conical plates. In accordance with the preferred embodiment of the present invention, essentially constant restoring and damping forces are achieved in the ball-in- cone configuration. A preferred embodiment of the invention comprises a first, mounting plate which is mounted to the foundation upon which the structure is supported. A second, oppositely disposed bearing plate is secured to the structure to be supported. Each of the plates comprises a concave, generally conical surface creating a conical cavity therebetween. A ball, for example, a generally spherical steel ball, is disposed between the two plates in the conical cavity region. The conical surfaces of the respective load plates are of shallow angle and preferably exhibit a collinear vertical axis.

At maximum lateral displacement, the ball is configured to contact a recessed perimeter, which condition defines maximum bearing displacement.

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As lateral forces are applied to the bearing assembly, the top load plate is displaced laterally with respect to the bottom load plate, such that the ball sandwiched therebetween rolls laterally across the load plates, such that the ball is raised to a higher elevation. As such, the gravitational forces acting on the structure produce a lateral force component tending to restore the structure to its original position.

In accordance with a further aspect of the present invention, vertical and horizontal bearing loads are suitably transferred through the ball from one plate to the opposite plate. This vertical-2-horizontal load ratio remains essentially constant on a cone surface in accordance with a preferred embodiment of the invention. This translated to an essentially constant restoring function. In accordance with alternate embodiments of the invention, non-linear restoring laws may be achieved by employing concave surfaces within one or both of the opposing load plates which are non-linear in their angle of inclination. Indeed, virtually any rotational surface may be approximated by combining conical, spherical and prismatic segments. In accordance with the further aspect of the present invention, a rubber, foam, or other sealant (gasket) may be employed about the perimeter of the adjoining load plates to prevent contamination of the conical cavity.

In accordance with yet a further aspect of the present invention, both the restoring and damping forces associated with the subject bearing are substantially constant and, thus , substantially independent of lateral displacement.

Brief Description of the Drawing Figures

The subject invention will be hereinafter described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and:

Figure 1 is an exploded perspective view of a preferred embodiment of an exemplary ball-in-cone seismic isolation bearing in accordance with the present invention;

Figure 2 is a cross-section view of a dual isolation bearing in accordance with the teachings of the present invention;

Figure 3 shows a multiple cone array of an exemplary isolation bearing in accordance with the present invention;

Figure 4 is a partial cross-section view of a conical segment, exhibiting a substantially linear inclination;

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Figure 5 is a partial cross-section view showing a non-linear bearing surface inclination;

Figure 6 is a partial cross-section view of a further embodiment of a non-linear bearing surface; Figure 7 is a top plan view of a modular load plate construction in accordance with the present invention;

Figure 8 is a cross-section view of the modular load plate shown in Figure 7; and

Figure 9 is a partial cross-section view of an exemplary pair of meeting load plates, with an accordion rubber gasket interposed therebetween. Detailed Description of Preferred

Exemplary Embodiments

Referring now to Figure 1, an exemplary isolation bearing assembly 10 suitably comprises an upper load plate 11A, a lower load plate 11B, respective anchor bolt holes 13 configured to receive configured anchor bolts 14, and a ball 12 configured for receipt within the region between respective plates 11A and 11B.

Each plate 11 suitably comprises a recess 15, bounded by a recess perimeter 16, for example a circular lip, shoulder, or the like.

When installed in a building, bridge, or other structure, upper bearing plate 11A is suitably anchored to the structure to be supported through the use of anchor bolts 14. Lower load plate 11B is suitably mounted to the foundation, e.g., a concrete slab or the like through the use of anchor bolts 14. In the nominal position, ball 12 is suitably centered within respective plates 11A and 11B, such that ball 12 is disposed within the respective apices 17 of plates 11A and 11B.

When a seismic dislocation or other activity exerts a lateral force on one of the load plates with respect to the other, the plates move laterally relative to each other, whereupon ball 12 advantageously travels from the apex 17 of each load plate toward recess perimeter 16. In accordance with one aspect of the present invention, when isolation bearing 10 is at its maximum lateral displacement, ball 12 is suitably in contact with the respective recess perimeters (16) of both upper load plate 11A and lower load plate 11 B.

When plates 11A and 11B are laterally shifted with respect to one another from their nominal position, the weight of the building or other structure supported by the bearing exerts a downward force on upper bearing plate 11A; this bearing force is

transferred through ball 12 to lower bearing plate 11B. Because of the inclined angle of recessed surface 15, a component of the vertical gravitational force exerted by the building or other structure manifests as a lateral (e.g., horizontal) restoring force tending to urge the load plates back to their nominal position, as discussed in greater detail below in conjunction with Figures 4-6.

Referring now to Figure 2, a dual cavity bearing 20 suitably comprises an upper load plate 21 A and a lower load plate 21 B each comprising dual recessed cones 23 characterized by an apex 25. Respective balls 24 are disposed in the intercavity region. In accordance with a preferred embodiment of the present invention, a suitable gasket 22, for example a rubber or foam gasket, may be adhered (e.g., glued) to one or both of the two plates. A gasket serves to keep dust and other debris from entering the intercavity region.

Referring now to Figure 3, a fcur-cone system 40 suitably comprises respective load plates 21, respective cones 23, and respective anchor bolt holes 26. In such multiple cone embodiments, it is anticipated that two adjacent balls (not shown for clarity) at one side will tend to be overloaded during applied rotational bearing stresses.

In accordance with a further aspect of the multiple cone embodiments, the present inventor has observed that the bearing capacity of the bearing system increases as a multiple of the number of ball/cone combinations employed. For example, a dual cone configuration (Figure 2) is suitably twice as strong as a single cone configuration, whereas a four-cone embodiment (Figure 3) is suitably four times as strong in its bearing capacity as a single ball configuration for equal materials and dimensions. In applications where high bearing rotation is anticipated, the subject seismic bearing assembly may be augmented by the use of a supplemental elastic or elastomeric plate placed under the load plate to increase the degree of bearing rotation which the system may accommodate.

Referring now to Figure 4, the basic geometry of a half-cone portion of surface 15 will now be described.

In the nominal position, ball 12 suitably rests at point C, corresponding to cone apex 25. In this position, the radius of contact between ball 12 (having a radius r) and surface 15 is shown as distance a and is characterized by arc a. When a lateral force is applied to the bearing, ball 12 travels up from its initial, rest position J to a displaced position K, shown in Figure 4 as its maximum displacement position. In its maximum

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displacement position, the radius of contact between ball 12 and the bottom load plate extends from point B to point D on the recess perimeter. During this movement, ball 12 rises by a distance h as it travels horizontal distance I. In the embodiment shown in Figure 4, the slope of surface 15 between points A and B is suitably constant, i.e., the height of surface 15 is a linear function of the radial distance from apex 25. Consequently, the first derivative of the slope with respect to the base is constant, resulting in a substantially constant restorative force. Stated another way, the restoring force for any displacement is suitably independent of the degree of displacement.

In accordance with a preferred embodiment of the present invention, the slope of surface 15 is suitably on the order of 1.43° to 12.68°, and more preferably in the range of 2.86° to 4.28°, and most preferably about 4°.

Referring now to Figure 5, an alternative embodiment of the present invention suitably comprises a composite restoring capability. More particularly, restoring surface 44 is suitably trilinear, such that surface 44 has a varying slope from apex 25 to recess perimeter 16. In accordance with the embodiment set forth in Figure 5, surface 44 suitably comprises a first segment extending between apex 25 and point A defined by radius r and traversing arc a. A second segment extends from point A to point E defined by radius r, which traverses an arc/?. A third linear segment extends from point E to point B. In the rest position, ball 12 contacts the region of surface 44 between apex 25 and point A. During the initial portion of lateral displacement, ball 12 travels along the arc length between point A and point E, wherein the system exhibits a non¬ linear restoring force which is a function of the slope of the segment between point A and point E. As lateral displacement increases, ball 12 enters the region between points E and B, whereupon the system exhibits a substantially constant restoring force, until near maximum lateral displacement wherein ball 12 travels between point B and point F, whereupon a third restoring force is exhibited by the bearing system which is a function of the slope of the segment of surface 44 between points B and F. In the embodiment shown in Figure 5, the slope of the segment between points A and E and the slope of the segment between points B and F is suitably the same; however, any suitable slope and, hence, variable restoring force may be employed in the context of the present invention.

Referring now to Figure 6, a ballooner composite restoring surface suitably comprises a first segment extending between apex 25 (point C) and point A

characterized by a first radius r. A second region between point A and point E is characterized by radius r^ and a third region between point E and point F is characterized by a radius r ₂ . It will be appreciated that the fourth region of surface 44, between point F and point D, is characterized by a radius r which corresponds to the radius of ball 12.

With continued reference to Figure 6, it will also be appreciated that any suitable combination of radius or linear surfaces may be employed in the context of the present invention. Moreover, in embodiments wherein more than one linear segments are employed, the linear segments need not be of the same slope. Referring now to Figures 7 and 8, a composite bearing plate 30 suitably comprises a central plug 32, a base plate 31, a central plug 32, weld lines 33, support rings 34, perimeter (or recess) plates 35, anchor bolt holes 37, and cone segment 36. For large plan size assemblies, the built-up bearing construction shown in Figures 7 and 8 may be more economical and easier to manufacture. The conical surface may be substantially prismatic without noticeable degradation in performance. Optionally, the prismatic surface may be machined or ground to provide a smoother restoring action. As best seen in Figure 7, economical construction of plate 30 may be achieved by welding together a plurality of substantially flat, planar plate segments 39. In accordance with the embodiments shown in Figures 7 and 8, the interstitial region between respective surface segments 39 and base plate 36 may be filled with a suitable material, e.g., concrete (not shown).

Referring now to Figure 9, an accordion-shaped rubber ring 27 may be suitably glued to one or more of respective oppositely disposed load plates 21. Such a rubber ring advantageously inhibits water, dust, debris, birds, and insects from entering the intercavity region.

In accordance with a further aspect of the present invention, the respective conical surfaces described herein may be suitably made from high-strength steel or other material exhibiting high-yield strength. In addition, the various surfaces may be coated with teflon or other protective layers. In accordance with a further aspect of the present invention, for a constant restorative force, the lateral bearing force is substantially independent of the lateral bearing displacement. Inasmuch as restoring forces are conservative in nature, and rolling friction represents a dissipative force, the relationship between the restorative

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forces and friction forces is essentially a constant function. These essentially constant dissipative and restorative forces have heretofore been unachievable in prior art systems.

In accordance with a further alternate embodiment of the present invention, only

5 one of the load plates need be eαuipped with a conical recess. That is, one of the load plates (either the upper or lower plate) may comprise a conical recess of the type discussed herein, whereas the oppositely disposed load plate may comprise an essentially flat surface.

In accordance with yet a further aspect of the present invention, the various 0 bearings discussed herein may be supplemented by external dampers to reduce bearing displacements.

It will also be appreciated that sole and masonry plates may be used in conjunction with the load plates discussed herein to provide proper horizontal alignment between opposing bearing plates in applications where either the foundation to which 5 the lower plate is attached or the structure to which the upper plate is attached is curved, sloped, or skewed.

In accordance with yet a further aspect of the present invention, the number and size of bearing assemblies used in any particular application may be configured to accommodate the desired bearing capacity of the load to be supported. In this regard, υ the contact pressure (Hertz stress) may be designed to approach the yield strength of the hardened steel ball (e.g., 80,000-120,000 psi).

In accordance with a further aspect of the present invention, a stainless steel ball- in-cone bearing assembly, particularly if properly insulated from the external environment with an appropriate gasket, would require no maintenance, inspection, or replacement 5 in service.

In accordance with yet a further aspect of the present invention, small-scale experiments with the subject bearing assemblies have exhibited an ability to translate north-south applied bearing movements to east-west forces. This dynamic orthogonality averages peak directional shocks favorably. These presumably random, automatic o averaging processes tend to decrease the bearing size and peak response forces which will be experienced in any particular application.

While the present invention has been described in conjunction with the preferred and alternate embodiments set forth in the drawing figures, it will be appreciated that

the invention is not so limited. Various modifications in the selection and arrangement of components and materials may be made without departing from the spirit and scope of invention as set forth in the appended claims.