Seismic Isolator

Abstract

A seismic isolator comprising: a first and a second plate-like coupling member which are arranged substantially horizontally one spaced apart above the other; and a movable sliding-block which is interposed between said plate-like coupling members, and rests in a freely sliding manner on the concave bottom of a depression realized on the exposed face of said first plate-like coupling member; the concave bottom being provided with at least one free-sliding area, which surrounds/flanks the stationary-standing area and is provided with a dynamic friction coefficient greater than that of the stationary-standing area.

Description

TECHNICAL FIELD

[0001] The present invention concerns a seismic isolator.

[0002] In greater detail, the present invention concerns a seismic isolator for small buildings, use to which the following discussion will make explicit reference without losing in generality.

BACKGROUND ART

[0003] As is known, seismic isolators are devices which are usually interposed between the foundation basement and the superstructure of the building, and are structured so as to reduce and at least partially dissipate the mechanical stresses which are transmitted to the superstructure of the building during seismic events.

[0004] The seismic isolators currently on the market are basically divided into two categories: elastomeric-type seismic isolators and pendular or "sliding" seismic isolators.

[0005] The elastomeric-type seismic isolators are basically made up of two coupling plates made of metal material, which are arranged horizontally and spaced one above the other; and of a large block of elastomeric material, which is interposed between and securely attached/anchored to both the coupling plates, and incorporates inside itself a series of metal sheets arranged horizontally and spaced above one another.

[0006] The lower coupling plate is structured so as to rest on and be stably anchored to the foundation basement of the building, while the upper coupling plate is structured so as to stably anchored underneath the superstructure of the building.

[0007] The block of elastomeric material is able to deform in presence of horizontal shear stresses, thus allowing the upper coupling plate to move horizontally with respect to the lower coupling plate, consequently modifying the dynamic behaviour of the isolated structure.

[0008] Sliding seismic isolators, on the other hand, are basically made up of two coupling plates made of metal material, which are arranged in horizontal position spaced one above the other; and of a large intermediate movable sliding-block which has a substantially non-deformable structure and rests in free sliding manner on both the coupling plates.

[0009] In greater detail, the intermediate sliding-block rests in free sliding manner on the concave bottom of a large lenticular-shaped depression which is formed in the centre of the exposed face of the upper and/or lower coupling plate.

[0010] Also in this case the lower coupling plate is structured so as to be stably anchored resting on the foundation basement of the building, while the upper coupling plate is structured so as to be stably anchored underneath the base of the superstructure of the building.

[0011] During the seismic event, the sliding seismic isolator allows the superstructure of the building to move freely in a horizontal direction with pendular movement, dissipating by friction a part of the seismic energy. At the end of the seismic event, instead, the concave profile of the bottom of the depression allows self-centring of the superstructure of the building on the foundation.

[0012] Unfortunately, although offering a high capacity of absorbing seismic waves, the elastomeric-type seismic isolators have an unstable behaviour in the presence of relatively reduced vertical loads, like those typical of a small building, therefore they are not suitable for isolating these types of buildings.

[0013] The sliding seismic isolators, on the other hand, are generally too costly to be used in small buildings, and furthermore they do not offer the same performance as the elastomeric-type seismic isolators.

DISCLOSURE OF INVENTION

[0014] Aim of the present invention is to provide a sliding seismic isolator with better performance than those currently known, and which is also cheaper to produce.

[0015] In compliance with the above aims, according to the present invention there is provided a seismic isolator as defined in claim 1 and preferably, though not necessarily, in any one of the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will now be described with reference to the accompanying drawings, which illustrate a non-limiting embodiment example thereof, in which:

[0017] FIG. 1 is a partially exploded perspective view of a seismic isolator realized according to the teachings of the present invention;

[0018] FIG. 2 is a section view of the seismic isolator shown in FIG. 1, with parts removed for clarity; whereas

[0019] FIG. 3 is a section view of a second embodiment of the seismic isolator shown in FIG. 1, with parts removed for clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] With reference to FIGS. 1 and 2, number 1 denotes as a whole a seismic isolator adapted to be interposed between the superstructure of a building and the foundation basement or other substructure of the same building, so as to significantly reduce the stresses transmitted to the superstructure of the building during seismic events.

[0021] Obviously, the seismic isolator 1 can also be interposed between the base of a marble statue and the supporting plane underneath, between the deck and the piers of a bridge, or between the ground resting feet of a large object (for example a large high voltage transformer) and the underlying reinforced concrete base, again in order to significantly reduce the mechanical stresses transmitted to the statue or to the large object during seismic events.

[0022] With reference to FIGS. 1 and 2, the seismic isolator 1 comprises: a first substantially non-deformable, plate-like coupling member 2 which extends horizontally and is adapted to be arranged with its lower face 2b stably resting on the ground or other supporting plane; a substantially non-deformable, movable sliding-block 3 which rests in free sliding manner on the exposed upper face 2a of the plate-like member 2; and a substantially non-deformable, second plate-like coupling member 4 which extends horizontally spaced above the plate-like member 2, is adapted to be arranged with its upper face 4b stably resting underneath the body to be seismically isolated, and lastly rests in free sliding manner on the top of the sliding-block 3.

[0023] In other words, plate-like members 2 and 4 are arranged in a substantially horizontal position spaced one above the other, and the movable sliding-block 3 rests in free sliding manner on surface of the exposed upper face 2a of plate-like member 2 and on surface of the exposed lower face 4a of plate-like member 4.

[0024] In greater detail, the lower plate-like member 2 is preferably made of metal material, and is preferably structured to be rigidly anchored on and in abutment with the foundation basement P or other substructure of the building to be seismically isolated.

[0025] Similarly, the upper plate-like member 4 is preferably made of metal material, and is preferably structured to be rigidly anchored in abutment beneath the superstructure (not shown) of the building to be seismically isolated.

[0026] Likewise to plate-like members 2 and 4, also the movable sliding-block 3 is preferably made of metal material.

[0027] In greater detail, in the example shown, the plate-like member 2 and/or the sliding-block 3 and/or the plate-like member 4 is/are preferably made of steel. Preferably the resting surfaces of the sliding-block 3 are furthermore covered with a layer of Teflon (polytetrafluoroethylene) or other similar material.

[0028] In a different embodiment, however, the sliding-block 3 could be made of high-strength plastic or composite material. For example, the sliding-block 3 could be made of reinforced rubber and optionally have the resting surfaces coated in Teflon or other similar material.

[0029] With reference to FIGS. 1 and 2, in particular, the exposed upper face 2a of plate-like member 2 is provided, preferably in a substantially central position, with a broad depression 5 which has a concave bottom 6 with radius of curvature R preferably substantially constant; and the sliding-block 3 rests in free sliding manner on the concave bottom 6 of the depression 5, within the perimeter of a given stationary-standing area/zone 6a which has an extent smaller than the overall extent of the concave bottom 6 and is preferably located at the point in which the depth of the depression 5 is maximum.

[0030] In other words, the movable sliding-block 3 is preferably arranged resting on the concave bottom 6 of the depression 5 in a position of stable equilibrium.

[0031] Preferably the lower part 3a of movable sliding-block 3 further has a shape locally substantially complementary to that of the concave bottom 6 of depression 5.

[0032] With reference to FIGS. 1 and 2, in the example shown, in particular, the depression 5 present on the exposed upper face 2a of plate-like member 2 is substantially lenticular in shape.

[0033] In greater detail, the concave bottom 6 of depression 5 is preferably shaped substantially like a spherical dome, and the lower part 3a of movable sliding-block 3 has a shape complementary to that of the resting point on the concave bottom 6.

[0034] In other words, the movable sliding-block 3 rests on the concave bottom 6 of depression 5 with a resting surface 3a shaped substantially like a spherical dome having a radius of curvature substantially equal to the radius of curvature R of the concave bottom 6.

[0035] Preferably the stationary-standing area 6a furthermore is substantially circular in shape and is preferably located substantially in the centre of the concave bottom 6 of depression 5.

[0036] With reference to FIGS. 1 and 2, in addition the concave bottom 6 of depression 5 also has one or more free-sliding areas that surround/flank the stationary-standing area 6a and have a dynamic friction coefficient greater than that specific of the stationary-standing area 6a; and the movable sliding-block 3 is able to slide freely on the concave bottom 6 of depression 5 also above said free-sliding areas.

[0037] Preferably the value of the dynamic friction coefficient increases as the distance of the free-sliding area from the perimeter of the stationary-standing area 6a raises.

[0038] With reference to FIGS. 1 and 2, in the example shown, in particular, the concave bottom 6 of depression 5 preferably has two annular-shaped free-sliding areas 6b and 6c, which are concentric to each other and completely surround the stationary-standing area 6a.

[0039] Free-sliding area 6b completely surrounds the stationary-standing area 6a, and has a dynamic friction coefficient preferably ranging from 110% to 130% of the dynamic friction coefficient specific of the stationary-standing area 6a.

[0040] Free-sliding area 6c completely surrounds the free-sliding area 6b, and has a dynamic friction coefficient preferably ranging from 130% to 150% of the dynamic friction coefficient specific of the stationary-standing area 6a.

[0041] Preferably the free-sliding areas 6b and 6c are also adjoined/adjacent to each other.

[0042] In greater detail, assuming that plate-like member 2 and movable sliding-block 3 are preferably made of steel and that the steel-steel dynamic friction coefficient at the stationary-standing area 6a is equal to approximately 0.42, the free-sliding area 6b has a dynamic friction coefficient preferably ranging from 0.44 to 0.54. The free-sliding area 6c, on the other hand, has a dynamic friction coefficient preferably ranging from 0.54 to 0.63.

[0043] With reference to FIGS. 1 and 2, in the example shown, in particular, the plate-like member 2, the movable sliding-block 3 and the plate-like member 4 preferably consist of an equal number of monolithic blocks made of high-strength steel.

[0044] Preferably the plate-like member 2 is moreover structured so as to be stably anchored to the ground, or better to the foundation basement P of the building, by means of a series of anchoring bolts 7 or other mechanical anchoring elements of known type.

[0045] With reference to FIG. 2, the surface of concave bottom 6 corresponding to the free-sliding area 6b is preferably coated with a layer of cast iron 8. The surface of concave bottom 6 corresponding to the free-sliding area 6c, on the other hand, is preferably coated with a layer of semi-metallic carbon ceramic material 9.

[0046] Alternatively, at the free-sliding areas 6b and/or 6c, the surface of concave bottom 6 may be sandblasted or surface-machined so as to locally increase the roughness of the surface, thus increasing the steel-steel dynamic friction coefficient.

[0047] With reference to FIGS. 1 and 2, similarly to the exposed face 2a of plate-like member 2, the exposed lower face 4a of plate-like member 4 is preferably provided, in a substantially central position, with a broad depression 12 having a substantially horizontal flat bottom 13; and the upper end 3b of movable sliding-block 3 rests in free sliding manner on the flat bottom 13 of depression 12.

[0048] Preferably the upper end 3b of movable sliding-block 3 moreover rests on the flat bottom 13 of depression 12 inside the perimeter of a given stationary-standing area/zone 13a that has an extent smaller than the overall extent of flat bottom 13, and is preferably located in the centre of the exposed face 4a of plate-like member 4; and the movable sliding-block 3 is able to slide freely on the flat bottom 13 of depression 12 also outside the stationary-standing area/zone 13a.

[0049] With reference to FIGS. 1 and 2, likewise plate-like member 2, in the example shown the plate-like member 4 preferably consists of a monolithic block made of high-strength steel, and is preferably structured to be stably anchored beneath the large body to be seismically isolated by means of a series of anchoring bolts 14 or other mechanical anchoring elements of known type.

[0050] Operation of seismic isolator 1 is easily inferable from the above description and does not require further explanations.

[0051] The advantages connected to the particular structure of seismic isolator 1 are remarkable.

[0052] Computer simulations have highlighted that, due to the free-sliding areas 6b, 6c with increased dynamic friction coefficient, the seismic isolator 1 is able to dissipate much more seismic energy than a traditional pendular seismic isolator, with all the ensuing advantages.

[0053] In addition, seismic isolator 1 has particularly restrained production costs and is therefore suitable for installation on small buildings.

[0054] Clearly modifications and variations can be lastly made to seismic insulator 1 without however departing from the scope of the present invention.

[0055] For example, the depression 5 having the concave bottom 6 could be realized on the exposed face 4a of upper plate-like member 4.

[0056] Or the depression 12 present on the exposed face 4a of upper plate-like member 4 could have a concave bottom with substantially constant radius of curvature.

[0057] With reference to FIG. 3, furthermore, in a more sophisticated embodiment the upper plate-like member 4 could comprise: two metallic plates 15 and 16 arranged in a substantially horizontal position, spaced one above the other; and an intermediate layer of elastomeric material 17 of suitable thickness which is interposed between and securely attached/anchored to the surface of metallic plates 15 and 16.

[0058] The upper metallic plate 15 is structured to be stably anchored beneath the superstructure of the building (not shown) or another large object to be seismically isolated.

[0059] The lower metallic plate 16 rests in free sliding manner on the upper part 3b of movable sliding-block 3.

[0060] In a less sophisticated embodiment, moreover, the movable sliding-block 3 may be rigidly integral with the exposed face 4a of upper plate-like member 4.

[0061] Lastly, the plate-like member 2 and/or the plate-like member 4 may consist of a preformed metal sheet with reduced thickness, cast on a block of epoxy resin or cement.

[0062] In other words, also the plate-like member 2 and/or the plate-like member 4 could be made of composite material.

Claims

1. A seismic isolator comprising: a first and a second plate-like coupling member which are arranged substantially horizontally one spaced apart above the other; and a movable sliding-block which is interposed between said plate-like coupling members, and rests in free sliding manner on the concave bottom of a depression realized on the exposed face of said first plate-like coupling member; the seismic isolator being characterized in that the movable sliding-block rests in a free sliding manner on said concave bottom, within the perimeter of a given stationary-standing area (6a) having an extent smaller than the overall extent of the concave bottom; and in that the concave bottom additionally has at least one free-sliding area which surrounds/flanks said stationary-standing area and is provided with a dynamic friction coefficient greater than that of the stationary-standing area; the movable sliding-block being able to freely slide on the concave bottom of the depression also above said free-sliding area.

2. Seismic isolator according to claim 1, characterized in that the concave bottom has a radius of curvature substantially constant.

3. Seismic isolator according to claim 2, characterized in that said concave bottom is shaped substantially like a spherical dome, and in that the stationary-standing area is located substantially at the centre of said concave bottom.

4. Seismic isolator according to claim 3, characterized in that said at least one free-sliding area is annular in shape and completely surrounds the stationary-standing area.

5. Seismic isolator according to claim 1, characterized in that the concave bottom has a plurality of free-sliding areas which surround/flank said stationary-standing area and are provided with a dynamic friction coefficient greater than that of the stationary-standing area; the movable sliding-block being able to freely slide on the concave bottom of the depression also above said free-sliding areas.

6. Seismic isolator according to claim 5, characterized in that the free-sliding areas are adjacent/adjoined to each other.

7. Seismic isolator according to claim 5, characterized in that the value of the dynamic friction coefficient increases as the distance of the free-sliding area from the stationary-standing area raises.

8. Seismic isolator according to claim 1, characterized in that the movable sliding-block rests in free sliding manner also on the exposed face of said second plate-like coupling member.

9. Seismic isolator according to claim 1, characterized in that the movable sliding-block is rigidly integral with said second plate-like coupling member.

10. Seismic isolator according to claim 1, characterized in that said first plate-like coupling member is made of metal material and/or in that said second plate-like coupling member is made of metal material.

11. Seismic isolator according to claim 1, characterized in that said movable sliding-block is made of metal material or plastic material or composite material.

12. Seismic isolator according to claim 1, characterized in that said first plate-like coupling member is adapted to be stably anchored to the ground or to another supporting surface, and in that said second plate-like coupling member is adapted to be stably anchored beneath the superstructure of the building or other body to be seismically isolated.

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