Title of Invention

A CONSTANT LONG PERIOD VIBRATION-PROTECTIVE PENDULUM ISOLATOR FOR STRUCTURES

Abstract

A constant long period vibration protective pendulum isolator (1) for structures, comprising a base (2) defining a load bearing surface (3) and at least one load transmitting slider (9) located in a load bearing component (13), translatablv against said load bearing surface, characterised in that the said load bearing surface is made of a hard non-corrosive material having coefficient of friction values from 0.01 to 0.20 and is parabolic defined by the geometric parameter "a" having values 0.02 to 23.0 per metre derived from the equation y = ax2, wherein "x" and "y" are slider displacements along X (horizontal) and Y (vertical) axes respectively from the centre of the parabolic load bearing surface and having values from 0.0 to 1.0m 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 freely in a concave cavity (11) at the basal end (12) of the load bearing component (13) and a convex bottom surface (19) translatablv located against the parabolic load bearing surface and the base and load bearing component are made of hard non-corrosive material.

Full Text

FORM 2 THE PATENTS ACT 1970 amended by the Patents (Amendment) Act of 1999 COMPLETE SPECIFICATION (SEE SECTION 10) TITLE A constant long 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 Indian Institute of Technology, Bombay, Powai, Mumbai - 400076, Maharashtra, India The foBowing specification particularly describes and ascertains the nature of this invention and the manner in winch it is to be performed : FIELD OF INVENTION This invention relates to a constant long 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 operability considerations. Many structures contain equipments and/or subsystems whose safety or functional requirements during vibratory motions may also be very important. Such equipments 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. Very large responses may occur when the fundamental time period of the subsystem is tuned to the dominant periods of the structure. Development of robust vibration control devices is an area of active research and development. A sliding device introduced between the structure and its base 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 are already known. A load transmitting slider is disposed between the load bearing surface and a load-bearing component which is rigidly 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 by the external vibration, as a result of which the shder shdes along with the structure on the load bearing surface and dissipates the energy from external vibrations as fiictional energy. The dynamic properties of the isolator are such that a large proportion of the energy from the external vibrations is filtered out. Thus the energy introduced into the structure is reduced thereby protecting the structure from the harmful effects of the vibrations. Due to the load bearing surface being concave and spherical, the displaced shder 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 load bearing surface, the restoring force developed in the displaced position of the shder 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 the isolator shortens for large displacement. Therefore, the time period of 4 the isolator varies with displacement and the isolator does not exhibit a constant time period. Usually the radius of curvature chosen ranges from 0.9m to 15.0m. This is because, for radii lesser than 0.9m, 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 flat to restore the structure to its original position after the vibrations. The usual range of radii of curvature results in isolator period ranging from 1.9 s to 7.8 s (frequency of 0.13 Hz to 0.53 Hz). The isolators with this range of period are generally effective for controlling the external vibrations with their dominant frequencies ranging from 1.0Hz to 10Hz. Isolators comprising concave spherical load bearing surface cannot be tuned to the frequency of the structure, when the structure frequency is greater than 0.53 Hz. Isolation device frequency higher than this is not practical for such load bearing surface. Therefore, this device can 5 not be used as Tuned Mass Damper (TMD) as the frequency of the device cannot be tuned with that of the structure on which it is installed. Another pendulum isolator of the above type comprises concatenation of a fixed number spherical concave sliding surfaces of increasing radii of curvature which become activated at different displacement levels (US Patent No 5056280). The restoring force at the points of change in curvature is discontinuous and hence may induce jerks in the structure during vibration. Due to the differing displacement levels offered by the load bearing surface it is not possible to achieve constant isolator time period. Due to the spherical shding surface the restoring force is also not bounded. Another pendulum isolator of the above type comprises a load bearing surface of three spherical shding 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 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 defining a shallow concave in a 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 the structure may experience a jerk at the apex where there is a change in curvature. Besides the frequency of vibration of the isolator cannot be explicitly defined due to the geometric profile of the recess. Structures can also be protected by using vibration absorbers, also called Timed Mass Damper (TMD), installed at or near the top of the structures. TMD comprises a mass, a stiffness element and a damping or energy dissipating mechanism. The mass and stiffness element of TMD are 7 selected such that the frequency of the TMD is tuned with that of the structure on which it is installed. The TMD effectively dissipates more energy and hence reduces the vibrations. If the frequency of TMD is not tuned with that of the structure on which it is installed the effectiveness of the device is greatly reduced. The prior art isolators can not be used with effective TMDs due to their variable frequency. OBJECTS OF INVENTION An object of the invention is to provide a constant long period vibration-protective pendulum isolator for structures having fundamental time periods from 0.3 s to 10.0s. Another object of the invention is to provide constant period vibration-protective pendulum isolator for structures that dissipates energy through friction and transmits reduced energy into the structure. 8 Another object of the invention is to provide a constant long period vibration protective pendulum isolator for use as a constant long period tuned mass damper for structures which protects the structure by absorbing the vibration energy induced in the structure due to the external vibration. DESCRIPTION OF INVENTION According to the invention there is provided a constant long 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 said load bearing surface, characterized in that the said load bearing surface is made of a hard non-corrosive material having coefficient of friction values from001 to 0.20 and is parabolic defined by the geometric parameter "a" having values 0.02 to 23.0 per metre derived from the equation y = ax2, wherein "x" and "y" are slider displacements along X (horizontal) and Y (vertical) axes respectively from the centre of the parabolic load bearing surface and having values from 0.0 to 1.0m 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 freely in a concave cavity at the basal end of the load bearing component and a convex bottom surface translatably located against the parabolic load bearing surface and the base and load bearing component are made of hard non-corrosive material. Preferably the parabolic load bearing surface is made of a material having co-efficient of friction from 0.02 to 0.10. The load bearing surface may be made of a hard non-corrosive material such as stainless steel and coated with wearing surface such as Teflon or Polytetraflouroethylene (PTFE), preferably PTFE. The base on which the parabolic surface is formed is made of metal such as stainless steel. 10 The slider may be made of material such as stainless steel. The shder may be covered with an elastic layer such as rubber and anchored to the basal end of the load bearing component by a flexible membrane such as rubber fixed to the shder and the load bearing component. This will prevent dust from entering the upper convex portion of the shder during shder motion and also holds the lubricant when used. The top and bottom surfaces of the shder may be coated with a wearing surface such as Teflon or PTFE, preferably PTFE. Alternatively, the top and bottom contact surfaces of the slider may be lubricated with a non-degrading lubricant such as graphite or silicon based lubricant provided between the outer surface of the shder and the elastic layer at the time of assembly. The shder may be articulated type or fixed type. 11 According to an embodiment of the invention the articulated shder is hemispherical 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 shder 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 shder originating from the bottom edges of the basal end and detachable portion, the spherical shder 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 shder is hemispherical defining a shear key at the convex top surface thereof and i 12 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. The preferred practical range of values for V are 0.0 to 1.0m, "y" are 0.0 to 0.5m and "a" are 0.02 to 23.0 per metre in the equation y = ax2. The load bearing component may be made of material such as stainless steel. In order to prevent foreign particles such as dust entering the contact surfaces between the load bearing surface and slider, a flexible material cover may be 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 rubber. The load bearing component and base may be fixed to the structure and foundation respectively by bearing plates, flange and bolts. Alternatively the base may be secured to the top or at any intermediate level of the structure by bearing plates, flange and bolts and the load bearing component is fixed to an additional mass or to the base of the remaining portion of the structure by bearing plates flange and bolts so that the pendulum isolator of the invention acts as a TMD. 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 constant long period vibration protective pendulum isolator for structures according to an embodiment of the invention; 14 Figure 2 is 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 shder according to another embodiment of the invention; Figure 5 is a sectional elevation of an articulated shder 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 shder of Fig 5; 15 Figure 8 shows disassembled sectional view of the basal end of the load bearing component of the articulated slider of Figure 5; Figure 9 is sectional elevation of an articulated slider according to another embodiment of the invention; Figure 10 is section at BB in Fig 9; Figure 11 is a sectional elevation of a constant long period vibration protective pendulum isolator for structures according to an embodiment of the invention used as a Tuned Mass Damper, and Figure 12 shows graphic representation of typical force-deformation relation of the constant period vibration protective pendulum isolator of Fig 1. 16 Referring to Figs 1 to 3 of the accompanying drawings, the constant long period vibration protective pendulum isolator 1 comprises a base 2 defining a parabolic load bearing surface 3 as herein described 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 with bolts 8 secured through the flange 4 and bearing plate 7 and anchored in the foundation. 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 j bearing component 13. For ease of construction the load bearing component and its basal end are separately made and rigidly fixed to each other for instance, by welding. The slider is covered with an elastic layer 14 and is anchored to the basal end of the load bearing component by a flexible membrane 15 fixed to the slider and the load bearing component (Fig 3). 16 j is a flange rigidly fitted to the upper end of the load bearing component. The load bearing component is rigidly fixed to the structure 6 against a bearing plate 17 with bolts 18 secured through the flange 16 and load bearing plate 17 17 and anchored in the structure. The shder comprises a convex bottom surface 19 translatably located against the parabolic load bearing surface. 20 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. Due to vibration motion experienced by the isolator, the shder tends to slide along the parabolic load bearing surface of the invention upwardly outwardly. Due to the load bearing surface being parabolic, the slope at any point on the load bearing surface is directly proportional to the displacement of the shder from the zero displacement position so that the restoring force is also proportional to the displacement of the shder. As a result, the frequency of the isolator for given geometric parameter "a" is a constant equal to "^/2ag", where "g" is the acceleration due to gravity. The gravitational force acting on the shder at progressively increasing heights of the parabolic surface from the centre thereof also tends to restore the shder to its original. The frictional force acting on the shder during sliding dissipates the vibration energy and thus reduces the energy 18 transmitted to the structure. By designing and selecting the geometric parameter of the load bearing parabolic surface, long time periods of the order of 0.3 s to 10.0 s may be achieved. Therefore, the isolator of the invention is suitable for very effective absorption of vibration motions due to for instance earthquakes, very heavy winds or machinery. Due to its constant long time period, the invention is also suitable for use as TMD. Referring to Fig 4 of the accompanying drawings, the slider 21 is fixed and hemispherical defining a shear key 22 at the top convex surface 23 thereof. 24 is a keyway formed in the concave cavity 25 at the basal end 26 of the load bearing component. The key way is adapted to receive the shear key on the top surface of the slider thereby locking the slider to the load bearing component. The convex bottom surface 27 of the slider is translatable against the load bearing surface. 28 is a wearing surface coating at the convex bottom surface of the slider. 19 Referring to Figs 5 to 8 of the accompanying drawings, 29 is an articulated spherical slider. The basal end 30 of the load bearing component is formed with a detachable portion 31 located in a corresponding cutout 32 at the bottom of the basal end. The basal end and detachable portion are provided with matching concave cavities 33 and 34 at one pair of abutting surfaces 35 and 36, 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 37 secured through holes 38, 39 and 40 in the basal end and detachable portion. 41 is a wearing surface coating on the slider. Referring to Figs 9 and 10 of the accompanying drawings, four articulated spherical sliders 42 are held in the basal end 43 and detachable portions 44 in the same manner as in Figs 5 to 8. The screws holding the detachable portions to the basal end are marked 45. Elastic layers covering the sliders are marked 46. 20 Because of its constant time period, the pendulum isolator of Figs 1 to 3 is used as TMD as shown in Fig 11 of the accompanying drawings by fixing the base 2 to the top of the structure 6 and by fixing the load bearing component 13 to an additional mass 47. The time period of the structure is chosen to be equal to that of the structure. Alternatively, the base may be fixed to a portion of the structure at an intermediate level thereof and the load bearing component may be fixed to the remaining portion of the structure. The force deformation hysteresis loop of Fig 12 of the accompanying drawings shows that the restoring force increases linearly with increase in sliding displacement. This linear variation of the restoring force provides constant period of the isolator. 21 We Claim : 1) A constant long period vibration protective pendulum isolator (1) for structures, comprising a base (2) defining a load bearing surface (3) and at least one load transmitting slider (9) located in a load bearing component (13), translatablv against said load bearing surface, characterised in that the said load bearing surface is made of a hard non-corrosive material having coefficient of friction values from 0.01 to 0.20 and is parabolic defined by the geometric parameter "a" having values 0.02 to 23.0 per metre derived from the equation y = ax2, wherein "x" and "y" are slider displacements along X (horizontal) and Y (vertical) axes respectively from the centre of the parabolic load bearing surface and having values from 0.0 to 1.0m 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 freely in a concave cavity (11) at the basal end (12) of the load bearing component (13) and a convex bottom surface (19) translatablv located against the parabolic load bearing surface and the base and load bearing component are made of hard non-corrosive material. - 22 - 2) A pendulum isolator as claimed in claim 1, wherein said parabolic load bearing surface is made of a hard non-corrosive material having coefficient of friction values from 0,02 to 0.10. 3) A pendulum isolator as claimed in claim 1 or 2, wherein said load bearing parabolic surface is made of stainless steel and coated with polytetrafluoroethy lene. 4) A pendulum isolator as claimed in any one of claims 1 to 3, wherein the base on which said parabolic surface is formed is made of stainless steel. 5. A pendulum isolator as claimed in any one of claims 1 to 4, wherein said slider is made of stainless steel. ■vt 6) A pendulum isolator as claimed in any one of claims 1 to 5. wherein said slider is covered with an elastic layer and is anchored to the basal end of said load bearing component by a flexible membrane fixed to said slider and said load bearing component, - 23 - 7) A pendulum isolator as claimed in claim 6, wherein said elastic layer is made of rubber. 8) A pendulum isolator as claimed in claim 6 or 7 wherein said flexible membrane comprises rubber. 9) A pendulum isolator as claimed in anyone of claims 1 to 5, wherein the top and bottom surfaces of said slider are coated with wearing surfaces. 10) A pendulum isolator as claimed in claim 9, wherein said wearing surfaces comprise polytetrafluoroethylene. 11) A pendulum isolator as claimed in anyone of claims 6 to 8, wherein said top and bottom contact surfaces of said slider are lubricated with a non-degrading lubricant such as graphite or silicon based lubricant provided between the outer surface of the slider and the elastic layer at the time of assembly. 12) A pendulum isolator as claimed in any one of claims 1 to 11, wherein said slider is articulated. - 24 - 13) A pendulum isolator as claimed in claim 12, wherein said articulated slider is spherical and the basal end of said 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. 14) A pendulum isolator as claimed in any of the claims 1 to 11, wherein said slider is a fixed slider. 15) A pendulum isolator as claimed in claim 14, wherein said fixed slider is hemispherical defining a shear key at the convex top surface thereof and the concave cavity at the basal end of said load bearing component is formed with a key way adapted to receive the key on the convex top surface of the slider, - 25 - 16) A pendulum isolator as claimed in anyone of claims 1 to 15, wherein said load bearing component is made of stainless steel. 17) A pendulum isolator as claimed in any one of claims 1 to 16, wherein a flexible material cover is provided over said load bearing surface and fixed to said bearing component and upper end of the base. 18) A pendulum isolator as claimed in claim 17, wherein said flexible material cover comprises rubber. 19) A pendulum isolator as claimed in any one of claims 1 to 18, wherein said load bearing component and base are fixed to the structure and foundation respectively by bearing plates, flange and bolts. 20) A pendulum isolator as claimed in anyone of claims 1 to 18, wherein said base is fixed to the top or at any intermediate level of the structure by bearing plates, flange and bolts and said load bearing component is fixed to an additional mass or to the base of the remaining portion of the structure by bearing plates, flange and bolts. - 26 -

Documents:

15-mum-2001-cancelled pages(10-09-2004).pdf

15-mum-2001-claims(granted)-(10-09-2004).pdf

15-mum-2001-claims(granted)-(10-9-2004).doc

15-mum-2001-correspondence(05-12-2004).pdf

15-mum-2001-correspondence(ipo)-(12-07-2004).pdf

15-mum-2001-form 1(04-01-2001).pdf

15-mum-2001-form 19(13-08-2003).pdf

15-mum-2001-form 2(granted)-(10-09-2004).pdf

15-mum-2001-form 2(granted)-(10-9-2004).doc

15-mum-2001-form 26(04-01-2001).pdf

15-mum-2001-form 3(04-01-2001).pdf

15-mum-2001-form 8(02-04-2004).pdf

15-mum-2001-power of authority(21-05-2004).pdf