Title of Invention

A VARIABLE PERIOD VIBRATION PROTECTIVE PENDULUM ISOLATOR FOR STRUCTURES

Abstract

A variable period vibration protective pendulum isolator (1) for structures (6). It comprises a base (2) defining a load bearing surface (3) and at least one load transmitting slider (9) located in a load bearing component (13) translatably against the load bearing surface. The load bearing surface is made of a hard non-corrosive material having coefficient of friction values from 0.01 to 0.20 and is spherical shallow concave surface whose inclination progressively increases and then decreases towards the centre such that the inclination at the centre is zero. The shallow concave surface is defined by the parametric equation 1_ V2r + 2dx sgn(x) y=b wherein b has values 0.01 to 1.0 m and d d + x sgn(x) has values 0.01 to 3.0 m such that the ratio b/d2 ranges between 0.1 and 100 per m and x and y are slider displacements along X and Y axes respectively from the centre of the load bearing surface and have values from 0.0 to 3.0 m and 0.0 to 0.5 m respectively. The load transmitting slider is made of a hard non-corrosive material and is spherical or hemispherical comprising convex top surface (10) located in a concave cavity (11) at the basal end (12) of the load bearing component and a convex bottom surface (14) translatably located against the load bearing surface. The base and load bearing component are made of hard non-corrosive material (Fig 1).

Full Text

FORM 2 THE PATENTS ACT 1970 (39 of 1970) COMPLETE SPECIFICATION (See Section 10; rule 13) TITLE A variable period vibration protective pendulum isolator for structures APPLICANTS Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India, an autonomous educational institute established in India under the Institutes of Technology Act 1961 INVENTORS Under Section 28(2) Dr Ravi Sinha and Murnal Pranesh, both Indian nationals and Of Civil Engineering Department, Indian Institute of Technology, Bombay, Powai, Mumbai 400076, Maharashtra, India The following specification particularly describes the nature of this invention and the manner in which it is to be performed : GRANTED 11-9-2001 9 JUL 2004 FIELD OF INVENTION This invention relates to a variable period vibration protective pendulum isolator for structures. The term structure wherever used in this specification includes any structure requiring vibration control such as building, bridge, industrial structure, equipment or machinery or secondary system or subsystem such as piping system. PRIOR ART Structures are often subjected to severe vibration motions due to, for instance, earthquakes, heavy wind or machinery. It is necessary to reduce the vibrations that are transmitted to the structures for safety, serviceability or operabihty considerations. Many structures contain equipment and/or subsystems whose safety or functional requirements during vibratory motions may also be very important. Such equipment or subsystems usually have small mass when compared to that of the structure and require independent design from that of the structure. Sometimes, the filtering effect of the structure on vibration forces also results in adverse performance of the subsystems. Reducing vibrations in structures is a challenging task due to the uncertainty involved in the properties of the input 2 vibrations and the structural properties. Development of robust vibration control devices is an area of active research and innovation. A sliding device introduced between the structure and its foundation is one of the most effective base isolators used to isolate and dissipate vibration energy. Vibration protective pendulum isolators comprising a spherical concave load-bearing surface fixed to the foundation are already known. A load transmitting slider is disposed between the load bearing surface and a load-bearing component, which is fixed to the structure. The slider is also provided with a convex surface at the bottom translatable in the load bearing concave surface (US Patent No 4644714). When structures comprising such isolators experience severe vibrations caused by, for instance, earthquakes, heavy wind or mechanical vibrations, the isolator is activated from the external vibration, as a result of which the slider slides along with the structure on the load bearing surface and dissipates the energy from external vibrations as frictional energy. The dynamic properties of the isolator are such that the energy from the external vibrations is filtered out. Thus the energy introduced into the structure is reduced and a substantial portion of the remaining energy is dissipated by the isolator thereby protecting the structure from harmful effects of vibrations. Due to the load bearing surface being concave and spherical, the displaced slider and the structure experience a force provided by gravity, which helps the structure restore itself near to zero displacement position after the vibrations. Because of the concave and spherical profile of the 3 load-bearing surface, the restoring force developed in the displaced position of the slider progressively increases with displacement. As a result for large displacements, the restoring force developed is very high which may have an adverse effect on the structure. Again due to the progressively increasing restoring force, the time period of oscillation of the isolator shortens for large displacement. Therefore, the time period of the isolator for large sliding displacements may approach near to that of the structure thereby increasing the structure response. Usually the radius of curvature of the load bearing surface that is chosen ranges from 0.9 m to 15.0 m. This is because, for radii less than 0.9 m, the concave load bearing surface becomes too narrow to accommodate large displacements occurring during vibrations. On the other hand, when the radius of curvature is greater than 15.0 m, the profile of the load bearing surface becomes too wide to restore the structure to its original position after the vibrations. The above range of radii of curvature results in isolator period ranging from 1.9s to 7.8 s (frequency of 0.13 Hz to 0.53 Hz). Isolators with this range of period are generally effective for controlling vibrations of structures with their dominant frequencies ranging from 1.0 Hz to 10 Hz. Another pendulum isolator of the above type comprises a load bearing surface of a concatenation of spherical concave sliding surfaces of increasing radii of curvature, which are transforming into one another at different displacement levels (US Patent No 5056280). The restoring force at the points of change in the curvature is discontinuous and hence may induce jerks in the structure during vibration. Due to the differing displacement 4 levels offered by the load bearing surface it is not possible to achieve continuous vibration of isolator time period. Because of the spherical nature of the load bearing surface the restoring force increases progressively and may become very large. Another pendulum isolator of the above type comprises a load bearing surface of three spherical sliding surfaces of concave, convex and concave curvatures which are transforming into one another at different displacement levels (US Patent No 5438807). Such pendulum isolator also generally suffers from the same drawbacks as those of US Patent No 5056280. Another type of pendulum isolator comprises a steel ball sandwiched between two fixed horizontal plates, which have a shallow, concave, conical recess (US Patent No 5599106). On experiencing an external vibration, the ball is displaced within the conical recess and on removal of the external vibration, the ball returns to the original position i.e. the conical apex which is the point of rest. During the oscillatory motion of the ball during vibration, the structure may experience jerks, ie, high frequency response at the apex where there is change in curvature. Besides the frequency of vibration of the isolator cannot be explicitly defined due to geometrical profile of the recess. 5 OBJECTS OF INVENTION An object of the invention is to provide a variable period vibration protective pendulum isolator for structures having fundamental time periods from 0.2 s to 6.0 s. Another object of the invention is to provide a variable period vibration protective pendulum isolator for structures, which dissipates energy through friction at sliding surface and transmits reduced energy into the structure. Another object of the invention is to provide a variable period vibration protective pendulum isolator for structures, which limits the restoring force so that the force transmitted to the structure is bounded irrespective of magnitude of sliding displacement of the isolator. DETAILED DESCRIPTION OF INVENTION According to the invention there is provided a variable period vibration protective pendulum isolator for structures, comprising a base defining a load bearing surface and at least one load transmitting slider located in a load bearing component, translatably against the load bearing 6 surface, wherein the load bearing surface is made of a hard non-corrosive material having coefficient of friction values from 0.01 to 0.20 and is spherical shallow concave surface, the inclination of the shallow concave surface progressively increasing and then decreasing towards the centre such that the inclination at the centre is zero, the shallow concave surface being defined by the parametric equation wherein b has values 0.01 to 1.0 m and d has values 0.01 to 3.0 m such that the ratio b/d2 ranges between 0.1 and 100 per m and x and y are slider displacements along X and Y axes respectively from the centre of the load bearing surface and have values from 0.0 to 3.0 m and 0.0 to 0.5 m respectively, the load transmitting slider is made of a hard non-corrosive material and is spherical or hemispherical comprising convex top surface located in a concave cavity at the basal end of the load bearing component and a convex bottom surface translatably located against the load bearing surface and the base and load bearing component are made of hard non-corrosive material. Preferably the load-bearing surface is made of a material having coefficient of friction values from 0.02 to 0.20. The load bearing surface may be made of material such as stainless steel which may be coated with a wearing surface such as polytetraflouroethylene (PTFE). 7 The base on which the load-bearing surface is formed may be made of material such as stainless steel. The slider may be made of material such as stainless steel. The slider may be coated with a wearing surface such as PTFE. An elastic layer such as rubber may be anchored to the basal end of the load bearing component and to the slider. The top and bottom convex surfaces of the slider may be coated with a wearing surface such as PTFE. The slider may be articulated type or fixed type. According to an embodiment of the invention the articulated slider has hemispherical top convex surface and is freely located in the concave cavity at the basal end of the load bearing component. According to another embodiment of the invention the articulated slider is spherical and the basal end of the load bearing component is formed with a detachable portion located in a corresponding cut-out at the bottom of the basal end, the basal end and the detachable portion being provided with matching concave cavities at one pair of 8 abutting surfaces thereof corresponding to the spherical slider originating from the bottom edges of the basal end and detachable portion, the spherical slider being held in the concave cavities at the one pair of abutting surfaces exposed and in contact with the load bearing surface, the detachable portion being rigidly held to the basal end. According to an embodiment of the invention the fixed slider is hemispherical defining a shear key at the convex top surface thereof and the concave cavity at the basal end of the load bearing component is formed with a key way adapted to receive the key on the convex top surface of the slider. Preferably x is 0.0 to 2.5 m and y is 0.0 to 0.4 m. The load bearing component may be made of material such as stainless steel. A flexible material cover may be provided over the load bearing surface and fixed to the load bearing component and upper end of the base. The flexible material cover may be made of material such as rubber. The load bearing component and base may be fixed to the structure and foundation of the structure respectively by bearing plates, nuts and bolts or other anchoring mechanisms. 9 Alternatively the base may be secured at any intermediate level of the structure by bearing plates, nuts and bolts and the load bearing component may be fixed to the bottom of the base of the remaining portion of the structure by bearing plates, nuts and bolts. Single or multiple isolators of the invention may be used in structures/equipments/subsystems/secondary systems. The following is a detailed description of the invention with reference to the accompanying drawings, in which, Figure 1 is a sectional elevation of a variable period vibration protective pendulum isolator for structures according to an embodiment of the invention; Figure 2 is a plan view of the load bearing surface of the isolator of Fig 1 without the flexible material cover, Figure 3 is enlarged sectional elevation of the articulated slider of the isolator of Fig 1; Figure 4 is a sectional elevation of a fixed type slider according to another embodiment of the invention; 10 Figure 5 is a sectional elevation of an articulated slider according to another embodiment of the invention; Figure 6 is a sectional view at A-A in Fig 5; Figure 7 shows disassembled isometric view of the basal end of the load bearing component of the articulated slider of Fig 5; Figure 8 shows disassembled sectional view of the basal end of the load bearing component of the articulated slider of Fig 5; Figure 9 is sectional elevation of an articulated slider according to another embodiment of the invention; Figure 10 is section at B-B in Fig 9; Figure 11 is graphic representation of typical force-deformation relation of the variable period vibration protective pendulum isolator of Fig l;and Figure 12 is graphic representation of frequency variation with sliding displacement of the isolator of Fig 1. 14 Referring to Figs 1 to 3 of the accompanying drawings, the variable period vibration protective pendulum isolator 1 comprises a base 2 defining a load bearing surface 3 rigidly fixed thereto. 4 is a flange rigidly fitted to the base. The base is rigidly fixed to foundation 5 of a structure 6 against bearing plate 7 and anchored in the foundation using bolts 8. 9 is a load transmitting articulated hemispherical slider comprising a convex top surface 10 located freely in a concave cavity 11 at the basal end 12 of a load bearing component 13. For ease of construction the load bearing component and its basal end are separately made and rigidly fixed to each other by for instance, welding. The slider comprises a convex bottom surface 14 translatably located against the load bearing surface. 15 is a wearing surface coating over the slider. 16 is an elastic layer anchored to the basal end of the load bearing component and to the slider. The elastic layer prevents dust entering the convex top surface of the slider during sliding motion thereof. 17 is a flange rigidly fixed to the upper end of the load bearing component, which is rigidly fixed to the structure against a bearing plate 18 and anchored in the structure using bolts 19. 21 is a flexible material cover disposed over the load bearing surface and fixed to the load bearing component and the upper end of the base to prevent foreign particles such as dust entering the contact surfaces between the load bearing surface and the slider. The load bearing surface is a spherical shallow concave surface whose inclination progressively increases and then decreases towards the centre such that the inclination at the centre is zero. The shallow concave surface is defined by the parametric equation stated above. Because of the 12 above geometric profile of the load bearing surface, the slope or inclination initially increases from the centre and then gradually decreases and approaches zero as it progresses towards the outer periphery. Due to the vibration motion experienced by the isolator, the slider tends to slide along the load bearing surface upwardly outwardly. The zero slope at the centre of the load bearing surface reduces the jerks or high frequency responses when die isolator begins to slide. Because of the geometric profile of the load bearing surface the slope of the sliding displacement of the slider initially increases and reaches a predefined maximum value and then gradually decreases to zero as it moves outwardly progressively. The restoring force being directly proportional to the slope of the load bearing surface at any point on the load bearing surface, it also initially increases and reaches a maximum value and then decreases slowly. As a result the force transmitted to the structure is bounded to a predetermined maximum value. The frequency of the isolator goes on reducing with increase in sliding displacement x outwardly along the X axis. The square of the isolator frequency is given by where wb is frequency of the isolator and g is the gravitational constant. Since the isolator time period varies inversely as the frequency, the above expression for frequency implies that the time period varies with sliding displacement. The expression also shows that the time period is shortest 13 when the shding displacement is zero and nonotonically increases as the sliding displacement increases. The gravitational force acting on the shder at progressively increasing heights of the load bearing surface from the centre thereof tends to restore the shder to its original position. The frictional force acting on the shder during shding dissipates some vibration energy and further reduces the energy transmitted to the structure. By designing and selecting the geometric parameters of the load bearing surface, magnitude and rate of variation of frequency of the isolator can be controlled as per requirements. The geometrical parameters are so chosen that the fundamental time period at zero shding displacement is between 0.25 to 6.05. Therefore, the isolator of the invention is suitable for reduction of vibration motions of structure which vary in magnitude and frequency. Referring to Fig 4 of the accompanying drawings, the shder 22 is fixed and hemispherical defining a shear key 23 at the top convex surface 24 thereof. 25 is a keyway formed in the concave cavity 26 at the basal end 27 of the load bearing component. The keyway is adapted to receive the shear key on the top surface of the shder thereby locking the shder to the load bearing component. The convex bottom surface 28 of the shder is translatable against the load bearing surface. 29 is a wearing surface coating at the convex bottom surface of the shder. Referring to Figures 5 to 8 of the accompanying drawings, 30 is an articulated spherical shder. The basal end 31 of the load bearing 14 component is formed with a detachable portion 32 located in a corresponding cutout 33 at the bottom of the basal end. Both the basal end and the detachable portion are provided with matching concave cavities 34 and 35 at one pair of abutting surface 36 and 37, respectively corresponding to the spherical slider. The concave cavities originate from the bottom edges of the basal end and detachable portion. The slider is held in the concave cavities exposed and in contact with and translatable against the load bearing surface. The detachable portion is rigidly held to the basal end by screws 38 secured through holes 39. 40 and 41 in the basal end and detachable portion. 43 is the wearing surface coating over the slider. Referring to Figures 9 and 10 of the accompanying drawings, four articulated spherical sliders 44 are held in the basal end 45 and detachable portions 46 in the same manner as in Figures 5 to 8. The screws holding the detachable portion to the basal end are marked 47. 48 is a wearing surface coating on the slider. Referring to Fig 11 of the accompanying drawings, the force-deformation hysteresis loop of the isolator shows that the restoring force first increases, reaches a peak and then starts decreasing slowly with increase in sliding displacement. This variation of the isolator force transmits a bounded force to the supported structure irrespective of the type of excitation. 15 Referring to Fig 12 of the accompanying drawings, it shows the typical variation of frequency of the isolator with displacement where w1 is the initial frequency of the isolator at zero sliding displacement and Wb is the frequency of the isolator. It is observed that the frequency of the isolator decreases sharply with increase in shding displacement and tends to approach zero for infinite shding displacement. This variation of the isolator frequency provides sufficient frequency separation between the excitation frequencies and the structure frequency thereby minimising the amplification of the response. 16 We Claim; 1) A variable period vibration protective pendulum isolator for structures, comprising a base defining a load bearing surface and at least one load transmitting slider located in a load bearing component, translatably against the load bearing surface, wherein the load bearing surface is made of a hard non-corrosive material having coefficient of friction values from 0.01 to 0.20 and is spherical shallow concave surface, the inclination of the shallow concave surface progressively increasing and then decreasing towards the centre, such that the inclination at the centre is zero, the shallow concave surface being defined by the parametric equation wherein b has values 0.01 to 1.0 m and d has values 0.01 to 3.0 m such that the ratio b/d2 ranges between 0.1 and 100 per m and x and y are slider displacements along X and Y axes respectively from the centre of the load bearing surface and have values from 0.0 to 3.0 m and 0.0 to 0.5 m respectively, the load transmitting slider is made of a hard non-corrosive material and is spherical or hemispherical comprising convex top surface located in a concave cavity at the basal end of the load bearing component and a convex bottom surface translatably located against the load bearing surface and the base and load bearing component are made of hard non-corrosive material. 17 2) A pendulum isolator as claimed in claim 1, wherein the load bearing surface is made of a material having coefficient of friction values from 0.02 to 0.20. 3) A pendulum isolator as claimed in claim 1 or 2, wherein the load bearing surface is made of stainless steel. 4) A pendulum as claimed in claim 3, wherein the load bearing surface is coated with a wearing surface such as polytetraflouroethylene. 5) A pendulum isolator as claimed in any of claims 1 to 4, wherein the base in which the load bearing surface is formed is made of stainless steel. 6) A pendulum isolator as claimed in any of claims 1 to 5, wherein slider is made of stainless steel. 7) A pendulum isolator as claimed in any of claims 1 to 6, wherein the slider is coated with a wearing surface and an elastic layer is anchored to the basal end of the load bearing component and to the slider, 8) A pendulum isolator as claimed in claim 7, wherein the elastic layer is made of rubber. 18 9) A pendulum isolator as claimed in claim 7 or 8, wherein the wearing surface comprises polytetrafluroethylene. 10) A pendulum isolator as claimed in any of claims 1 to 9, wherein the top and bottom surfaces of the slider are coated with wearing surface such as polytetrafluroethylene. 11) A pendulum isolator as claimed in any of claims 1 to 10, wherein the slider is articulated. 12) A pendulum isolator as claimed in claim 11, wherein the articulated slider has hemispherical top convex surface and is freely located in the concave cavity at the basal end of the load bearing component. 13) A pendulum isolator as claimed in claim 11, wherein the articulated slider is spherical and the basal end of the load bearing component is formed with a detachable portion located in a corresponding cut-out at the bottom of the basal end, the basal end and the detachable portion being provided with matching concave cavities at one pair of abutting surfaces thereof corresponding to the spherical slider originating from the bottom edges of the basal end and detachable portion, the spherical slider being held in the concave cavities at the one pair of abutting surfaces exposed and in contact with the load bearing surface, the detachable portion being rigidly held to the basal end. 19 14) A pendulum isolator as claimed in any of claims 1 to 10, wherein the slider is fixed slider. 15) A pendulum isolator as claimed in claim 14, wherein the fixed slider is hemispherical defining a shear key at the top convex surface thereof and the concave cavity at the basal end of the load bearing component is formed with a key way adapted to receive the key on the convex top surface of the slider. 16) A pendulum isolator as claimed in any of claims 1 to 15, wherein x is 0.0 to 2.5 m and y is 0.0 to 0.4 m. 17) A pendulum isolator as claimed in any of claims 1 to 16, wherein the load bearing component is made of stainless steel. 18) A pendulum isolator as claimed in any one of claims 1 to 17, wherein a flexible material cover is provided over the bearing surface and fixed to the bearing component and upper end of the base. 19) A pendulum isolator as claimed in claim 18, wherein the flexible material cover comprises rubber. 20 20) A pendulum isolator as claimed in any one of claims 1 to 19, wherein the load bearing component and base are fixed to the structure and foundation of the structure respectively by bearing plates, nuts and bolts. 21) A pendulum isolator as claimed in any of claims 1 to 19, wherein the base is fixed at any intermediate level of the structure by bearing plates, nuts and bolts and the load bearing component is fixed to the bottom of the remaining portion of the structure by bearing plates, nuts and bolts. 22) A variable period vibration protective pendulum isolator for structures substantially as herein described particularly with reference to Figs 1, 2 and 3 or Fig 4 or Figs 5, 6, 7 and 8 or Figs 9 and 10 of the accompanying drawings. (M A Jose) of DePENNING & DePENNING Agent for the Applicants Dated this 6th day of September 2001. 21

Documents:

867-mum-2001-abstract(11-9-2001).doc

867-mum-2001-abstract(11-9-2001).pdf

867-mum-2001-cancelled pages(11-9-2001).pdf

867-mum-2001-claims(granted)-(11-9-2001).doc

867-mum-2001-claims(granted)-(11-9-2001).pdf

867-mum-2001-correspondence(14-1-2005).pdf

867-mum-2001-correspondence(ipo)-(14-10-2004).pdf

867-mum-2001-drawing(11-9-2001).pdf

867-mum-2001-form 1(11-9-2001).pdf

867-mum-2001-form 19(3-10-2003).pdf

867-mum-2001-form 2(granted)-(11-9-2001).doc

867-mum-2001-form 2(granted)-(11-9-2001).pdf

867-mum-2001-form 26(11-9-2001).pdf

867-mum-2001-form 3(11-9-2001).pdf

867-mum-2001-form 8(9-7-2004).pdf

abstract1.jpg