SEISMIC DISSIPATION MODULE MADE UP OF COMPRESSION-RESISTANT SPHERES IMMERSED IN A VARIABLE LOW DENSITY MATERIAL

Abstract

Seismic isolators, namely devices used for isolating the load-bearing structure of buildings from the effects of an earthquake are disclosed and include a seismic dissipation and isolation panel or module made up of compression-resistant spheres, made of sintered alumina, bound by variable low density substances, polyurethane foams or polystyrene or other similar material, to be used in new buildings by placing it between a reinforced concrete bed to be made on the ground and the foundation structures of the building, so that, in the event of an earthquake, there can be movements of the building independent from those of the ground on which it is built, so absorbing and isolating the seismic wave and therefore reducing the effects on the structures until, in theory, they cancel them.

Description

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

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STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

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REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention concerns the industry for making seismic isolators, namely devices used for isolating the load-bearing structure of buildings from the effects of an earthquake and consists of a seismic dissipation and isolation panel or module made up of compression-resistant spheres, made of sintered alumina, bound by variable low density substances, polyurethane foams or polystyrene or other similar material, to be used in new buildings by placing it between a reinforced concrete bed to be made on the ground and the foundation structures of the building, so that, in the event of an earthquake, there can be movements of the building independent from those of the ground on which it is built, so absorbing and isolating the seismic wave and therefore reducing the effects on the structures until, in theory, they cancel them.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

Seismic events are the cause of considerable damage to both concrete and masonry buildings, with well-known consequences on the life of many people. Buildings are anchored to the ground by various types of foundations; they are consequently totally affected by the seismic wave that propagates through the ground to the foundations and therefore to the building, so producing forces that cause considerable stresses to the structural masses, which it is attempted to remedy by laying considerable dimensions of structures and of metal reinforcements that can withstand these forces as much as possible.

To contain the uncertainties due to the uncertainty of the determination of the structural modelling parameters and guarantee good behaviour of the structures under seismic actions, specific measures must be adopted, which are listed below, aiming at ensuring ductility characteristics to the structural elements and to the building as a whole.

When an earthquake occurs, the base of the isolated building can move in all horizontal directions compared to the foundations; therefore, after a movement, it is necessary for the building to return to its original position, if the residual movements are not of small magnitude compared to the building. To that end, the base of the building must be provided with suitable re-centring systems, also called auxiliary devices, whose function is to dissipate energy and/or re-centre the system and/or to provide lateral constraint of the structure.

Devices that can re-centre the structure and also dissipate energy may include hydraulic devices or devices based on the particular mechanical properties of Shape Memory Alloys (SMA). These materials, typically made up of nickel-titanium alloys, have the ability to “remember” their original shape, which is unusual for other types of materials.

In general, movements experienced by the isolated structures as a consequence of seismic action must fall within tolerable values to contain the dimensions of the structural joints and not cause problems to the connections of the installations/systems. For isolated structures, flexible connections should in fact be envisaged for all the installations/systems that, from ground level, are connected to the superstructure.

Foundation structures must withstand the effects resulting from the response of the ground and the structures above, without permanent movements that are incompatible with the reference extreme state.

Buildings must be provided with structural systems that will guarantee stiffness and resistance to the two orthogonal-horizontal components of seismic actions.

The foundation system must be provided with high extensional stiffness in the horizontal plane and with sufficient flexural stiffness.

The structural elements of the foundations, which must be sized on the basis of the stresses transmitted to them from the structure above, must have non-dissipative behaviour, irrespective of the structural behaviour attributed to the structure bearing down on them.

By inserting isolators between the foundations and the elevation structures, the frequencies of the earthquake are uncoupled from the frequencies of the elevation structure and so the development of resonance phenomena is prevented.

In the event of seismic stress, the insertion of isolators allows the proper period of vibration of the structure to be increased so moving it away from the area of the response spectrum with greater accelerations.

This effectively causes a dynamic uncoupling of the building in relation to the ground (“filter” effect), so as to reduce transmission of the energy supplied by the seismic action to the superstructure. As a consequence of this last, the foundation-isolators-structure system can dissipate the seismic energy of the ground: the dissipation is almost exclusively concentrated in the isolation devices, which dissipate the seismic energy transmitted to them from the foundations at the expense of large plastic deformations, through wide hysteresis cycles. This allows the superstructure to have a response practically in elastic field by remaining almost immobile compared to the motion of the ground. This considerably changes the seismic input, since, by reducing the accelerations transmitted to the building, the response capacity of the structure to the ultimate collapse strength and to the extreme state of damage is considerably raised.

In addition to protecting the load-bearing structure, these devices also allow the non-structural parts and all it contains to be protected. In fact, as a consequence of the almost total absence of intermediate landing deformations (drift), this technology allows the prevention of cracks or damage to infills, partition walls, installations/systems or to goods inside buildings, such as museums or libraries, data processing centres, etc. This allows the damage caused to the structures by an earthquake to be minimized or completely eliminated, so maintaining unchanged the activity carried on in it, even after the occurrence of a severe telluric event.

During an earthquake, the isolated structure behaves almost like a rigid body that tends to remain still compared to the vibrations of the ground.

Using seismic isolators, a structure is designed that remains in elastic field even during the most violent earthquakes and keeps intact the energy dissipative capacity given by ductility.

Currently, in the field of seismic engineering, there are three categories of isolators and various types for each category.

Isolators made of elastomeric material and steel are made up of layers of elastomeric material (natural rubber or suitable artificial materials) alternated with steel plates, having the predominant function of confining the elastomer, and are arranged in the structure so as to withstand the rated horizontal actions and deformations through actions parallel to the position of the layers and of the vertical loads through actions perpendicular to the layers.

They are usually of circular design, but can also be made with square or rectangular section. They are characterized by reduced horizontal stiffness, high vertical stiffness and appropriate dissipative capacity.

Elasto-plastic isolators are made up of elements that stay elastic when there are just vertical loads but plasticize when there are horizontal actions higher than a set threshold.

Thanks to their high dissipation capacity, elasto-plastic isolators have the task of limiting the transfer of stresses to the substructures, and so guarantee a better response of the entire construction to a seismic event.

Sliding or rolling isolators, made up respectively of steel and Teflon supports and of supports on roller or spheres, are all characterized by low friction resistance values. Therefore, whereas for elasto-plastic isolators and for those made of elastomeric material and steel, the damping needed to contain the relative movements of the two separate structures is ensured by the strongly hysteretic behaviour of the material with which they are made, for sliding isolators and for rolling isolators, it is necessary to place suitable energy dissipators in parallel.

The dynamics of these types of isolators is complex, since the sliding process is inherently non-linear.

Some dissipators, called viscoelastic dissipators, exploit the viscous behaviour of materials such as plastics, mineral oils and silicone. Other dissipators, called elasto-plastic dissipators, exploit the plasticization of metallic materials to dissipate energy in hysteresis cycles. Finally, so-called friction dissipators exploit the friction between suitably treated metal surfaces that slide against each other.

In addition to the aging of elastomers (rubbers) and thermoplastic polymers (Teflon), the physical and chemical properties of the adhesives used to glue the steel sheets to the rubber, as well as those of the linear chain organosilicon polymers (silicone oils and greases) used in viscoelastic dissipators, possibly arranged in parallel to sliding or rolling isolators, are also important for the purposes of durability.

Moreover, elasto-plastic isolators and those made of elastomeric material and steel are particularly vulnerable in the event of fire and must be suitably protected from such an eventuality or used together with devices that can replace them if they are destroyed.

In the current art, there are also ENEA's aseismic marble bases for the Bronzi di Riace.

These belong to the family of seismic isolators developed by ENEA for the protection of delicate instruments. These are passive and/or semi-passive non-invasive seismic protection devices made up of two superimposed blocks of marble on the internal surfaces of which, in a specular way to the two blocks, four bowls have been hollowed out whose geometry is a rotation ellipsoid where four marble spheres are placed, which, with their rolling, give the requirements of large movements, low stiffness and low friction required to maximize seismic isolation.

When there is an earthquake, it will be the part beneath the base to be subjected to the seismic action and this will be able to move with the ground without transmitting the stresses to the upper part, since they are completely absorbed by the movement of the spheres inside the cavities hollowed out in the marble. The movement of the spheres makes the protection system not very rigid with very low friction, characteristics that minimize the stresses of the earthquake or render them almost null. The new aseismic marble base is particularly suitable for statues vertically developed that have a very small base and are therefore particularly vulnerable to horizontal seismic actions, which can compromise their balance and cause them to tip over.

This type of seismic isolation cannot be used for houses and flats since the materials used for making this device, if used for large areas, become very expensive in terms of both raw material and installation, and therefore the use of these aseismic bases with marble spheres is limited to works of art.

The different types of seismic dissipators or isolators on the market are very costly and made with a highly specialized technology, and even their installation cannot be carried out by an ordinary construction firm.

The rolling mechanical isolators described in patent “MICALI” No. 1146596 are made entirely of steel or other suitable rigid material and each made up of a pair of circular concave elements with a sphere interposed of diameter not less than the sum of the heights of the two concavities. According to this patent, by setting the concave elements in two reinforced concrete beds or net-like structures with one resting directly on the ground and the other on the spheres, only the lower bed or net-like structure is forced to undergo any horizontal seismic movements of the ground whereas the upper one, thanks to the rolling of the spheres beneath, can follow the calm inertia of the building and stay nearly immobile because it is forced only to undergo brief upward traverses due to the momentary movement of the lower concave elements compared to the upper ones set in it.

The limit of these rolling mechanical isolators regards the compressive strength of the spheres because of the small contact with the relevant concave rolling seats and the consequent need for large numbers or large dimensions. WO 99/07966 discloses a friction ball, made of either plastically deformable homogeneous material (lead, aluminium, brass, iron, steel, etc.) or elastomeric material, which is deformed when it supports a weight; said deformation generating a frictional force which resists rolling motion in the deformed ball.

The limit of these friction balls regards both the expensive costs of the materials they are made of and the low durability over time in terms of resistance thereof.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to make a seismic isolator made up of raw materials that are easy to find on the market, that have very low costs but have technical characteristics, in terms of density and strength, that allow an identical response for each event to be had in case of repeated earthquakes, and also involve no maintenance costs, since the components do not need to be replaced. Moreover, the isolator will form an excellent insulation from rising damp given the quality of aggregate of the sintered alumina spheres. It is another object of the present invention to make a seismic isolator that can withstand a multidirectional seismic input so that, in the event of an earthquake, there can be movements of the building independent from those of the ground on which it is built, so absorbing and isolating the seismic wave and therefore reducing the effects on the structures until, in theory, they cancel them.

It is a further object of the present invention to make a seismic isolator that can avoid transmitting the induced seismic forces on the building, so giving a reduction in structural dimensioning and, at the same time, maintenance of the functionality of the building.

These and other objects are obtained with the present invention that concerns a panel or module to be used in new buildings, to be installed between a reinforced concrete bed to be made on the ground and the foundation structures of the building, such as for example a reinforced concrete beam or foundation bed, so that, in the event of an earthquake, there can be movements of the building independent from those of the ground on which it is built, so absorbing and isolating the seismic wave and therefore reducing the effects on the structures until, in theory, they cancel them.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be more readily apparent from the description of a preferred, but not exclusive, embodiment of the product that is the subject of the present patent application, illustrated by way of non-limiting example in the drawing units in which:

FIG. 1 shows a plan view and a cross-sectional view of a prefabricated panel or module (1) made up of spheres (2), with a pre-set centre-to-centre distance between them that changes depending on the point load (load acting on a single point of the sphere) that it is wished make the sphere support, made of sintered alumina, bound by variable low density substances, polyurethane foams or polystyrene or other similar material (3);

FIG. 2 is a cross-section:

• • of the prefabricated panel or module (1) made up of spheres (2) made of sintered alumina and bound by variable low density substances, polyurethane foams or polystyrene or other similar material (3);
  • of the reinforced concrete bed (4) of the foundation resting the ground (5) and bounded on the upper part by the “isolation interface”, by “isolation interface” meaning the separation surface on which the isolation system is active;
  • of the reinforced concrete beam or foundation bed (6);
  • of the building (7) with column (8).

FIGS. 3 and 4 show an alternative embodiment of the prefabricated panel or module (1) in which:

FIG. 3 shows a plan view and a cross-sectional view of a prefabricated panel or module (1) made up of spheres (2), whose movement capacity is localized inside a circular area (9) and having a pre-set centre-to-centre distance between them that changes depending on the point load (load acting on a single point of the sphere) that it is wished make the sphere support, made of sintered alumina, bound by variable low density substances, polyurethane foams or polystyrene or other similar material (3);

FIG. 4 is a cross-section:

• • of the prefabricated panel or module (1) made up of spheres (2) made of sintered alumina, with capacity to move inside a localized area (9) and bound by variable low density substances, polyurethane foams or polystyrene or other similar material (3);
  • of the reinforced concrete bed (4) of the foundation resting the ground (5) and bounded on the upper part by the “isolation interface”, with “isolation interface” meaning the separation surface on which the isolation system is active;
  • of the reinforced concrete beam or foundation bed (6);
  • of the building (7) with column (8).

DETAILED DESCRIPTION OF THE INVENTION

In the description below, the following terms will be used, of which the definition is given:

• • “substructure” or “first foundation”, the part of the structure situated below the interface of the isolation system and that includes the foundations, generally having negligible horizontal deformability and directly subject to the movements imposed by the seismic movement of the ground;
  • “superstructure” or “second foundation”, the part of the structure situated above the isolation interface, and therefore isolated.

The polyurethane or polystyrene or other similar material (3) of the prefabricated module (1) is used to support the concrete casting of the superstructure in the first 28 days of curing of the said concrete.

The sintered alumina with which the spheres (2) of the prefabricated module (1) are made is a ceramic material resulting from the sintering of alumina, a substance present in bauxite, consisting of a thermal and mechanical process through which the powdered materials are reduced to a compact mass of a given shape; it combines the advantages of aluminium alloys and of powder metallurgy.

The sintered alumina spheres are characterized by very high hardness and compressive strength and therefore high resistance to axial loads, such that laboratory tests show that a sintered alumina sphere, about 5 cm in diameter, subjected to a vertical axial load of 9,000 kg, does not show any plastic effect on its contact surface.

The advantages of aluminium alloys are:

• • low specific weight (about 2.7 g/cm);
  • good corrosion resistance;
  • remarkable mechanical properties;
  • good wear resistance;
  • good fatigue resistance;

The advantages of powder metallurgy are:

• • low production costs;
  • good control of tolerances without subsequent processing;
  • possibility of obtaining complex shapes at limited cost.

The thickness of the prefabricated panel or module (1) is equal to the diameter of the spheres (2), (example: 3-5-8 cm, etc.) with a variable surface area that is suitable for transport, (example: 3.00×1.50 m, etc.) or below standard sizes.

The installation of these prefabricated panels or modules (1) envisages that they be placed touching each other on the horizontal plane, between the first and second foundation.

The sintered alumina spheres (2) should be covered with a suitable additive on the market, a silicone release agent, to ensure that the polyurethane or polystyrene or other similar material (3) does not come into contact with the spheres (2), since these must be allowed the possibility of rotating independently from the structure made of binding material (3) that surrounds them.

The possibility of multidirectional rotation of the spheres (2) in the event of an earthquake absorbs and isolates the horizontal oscillating motion of the ground (5) without transmitting stresses to the superstructure of the building (7), which, by inertia, will tend to maintain the position, so reducing the well-known disastrous effects.

The binding material (3), of the sintered alumina spheres (2), at low and variable density allows their controlled rotation. The prefabricated module (1) does not undergo deformations during the earthquake, since the sintered alumina spheres (2) have high compressive strength and are without plastic consequences; consequently, the response, with dissipative-isolating effect, will always be the same even during the next earthquake shock, without the panel (1) components ever having to be replaced.

For the system of the foundations (6), both the intradosal ones of the isolator and the extradosal ones, normal strength concretes Rck 30 can be used, with usual loads without plastic effects on the concrete due to the sintered alumina sphere (2) of the isolator (tests carried out in a laboratory). For particular loads on the foundation (6), a foundation concrete with suitable strengths will be used.

The centre-to-centre distances between the sintered alumina spheres (2) may, in particular cases, be adapted to the requirements of the weights above so as to optimize the point load on the sphere (2).

According to a further embodiment of this prefabricated panel or module (1) for seismic dissipation and isolation, the binding material (3) of the sintered alumina spheres (2) is shaped in such a way that each sphere (2) must move inside a localized circular area (9) that delimits its possibility of movement and, in the same way, allows its controlled rotation.

The materials and the dimensions of the above-described invention, illustrated in the accompanying drawings and later claimed, may be varied according to requirements. Moreover, all the details may be replaced by other technically equivalent ones without for this reason straying from the protective scope of the present invention patent application.

Claims

1. Seismic dissipation module to isolate a load-bearing structure of buildings from the effects of an earthquake, said seismic dissipation module comprises a prefabricated panel to be installed between a reinforced concrete bed to be made on a ground and foundation structures of a building, wherein said prefabricated panel is made up of compression-resistant spheres arranged inside the prefabricated panel with a pre-set centre-to-centre distance between the compression-resistant spheres, and said compression-resistant spheres are made of sintered alumina and bound by variable low density substances, polyurethane foams or polystyrene.

2. Seismic dissipation module of claim 1, wherein the compression-resistant spheres are covered with a additive such as a silicone release agent.

3. Seismic dissipation module of claim 1, wherein the thickness of the prefabricated panel is equal to the diameter of the compression-resistant spheres, with a variable surface area that is suitable for transport.

4. Seismic dissipation module of claim 1, wherein said variable low density substances, polyurethane foams or polystyrene binding the compression-resistant spheres are shaped in such a way that each of the compression-resistant spheres must move inside a localized circular area.