AU620587B2 - Improvements in or relating to energy absorbers - Google Patents

Description

~17" t t COMMONWEALTH OF AUSTRALIA Patent Act 1952 2 0 587 COM P L E T E SPECIF I CATI N

(ORIGINAL)

Class Int. Class

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Application Number Lodged Complete Specification Lodged Accepted Published SPriority: Related Art United States of America No. 694,253 24 January 1985

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Name of Applicant Address of Applicant S DEVELOPMENT FINANCE CORPORATION OF NEW ZEALAND Development Finance Centre, Corner Grey and Featherston Streets, Wellington, New Zealand Actual Inventor I an George Buckle Address for Service F.B. RICE CO., Patent Attorneys, 28A Montague Street, BALMAIN. 2041.

Complete Specification for the invention entitled: "Improvements in or Relating to Energy Absorbers" The following statement is a full description of this invention including the best method of performing it known to Us:- -2- Background of the Invention This invention relates to energy absorbers used in conjunction with large structures to reduce the influence of external induced motion on such structures.

Cyclic shear energy absorbing devices are known which employ the cyclic plastic deformation of certain materials beyond the elastic limit for the absorption of kinetic energy. Such absorbing devices are typically interposed between a building support member and a base member, or between two structural support members, in order to convert portions of the kinetic energy into heat in the absorbing material and thus reduce the motion imparted to the structure by externally induced forces, such as an earthquake or high winds. U.S. Patent No.4,117,637 issued October 3, 1978, to Robinson for "Cyclic Shear Energy Absorber", the disclosure of which is hereby incorporated by reference, illustrates 0 several geometrical configurations of the basic cyclic shear energy absorber device.

The basic device includes a pair of spaced coupling members, typically plates, each one of which is designed to be coupled to an individual structural member. When used in a building environment, for example, one of the coupling members is configured to be attached to a support piling, while the other coupling member is configured to be attached to a support pillar, beam or the like. Arranged between the two coupling members is a solid plastically cyclically deformable mass of S material, typically lead, which provides the energy absorption function. Some configurations of this type of device further include an additional resilient pad structure which surrounds the energy absorbing mass and provides resilient vertical support between the two coupling 4 -3 members, usually by means of a sandwich comprising alternate layers of a resilient material rubber) and a stiffener material steel, aluminium or the like).

In use, when externally induced forces result in relative lateral motion between the two coupling members, the solid energy absorbing mass is cycled beyond its elastic limit, converting some of the energy into heat and storing the remaining energy when the mass is in the deformed state, the latter acting as a driving force which tends to return the material to its original mechanical properties. As a consequence, the energy transmitted to woo* or through the structure is converted into heat rather o o' building. Consequently, structures incorporating such S 15 absorbers have a higher safety factor than those relying on the ductile behaviour of structural members to dissipate energy (which will be damaged by a severe earthquake and will be difficult to repair or replace), *000 oo° and those using rubber dampers, (which function in a 20 spring like fashion and dissipate only small amounts of externally imparted energy).

While cyclic energy absorbers of the above type have been found to function well in many applications, in some applications premature degradation of the energy absorbing o 25 mass after a small number of oscillations has been observed.

This is due to a lack of confinement about the absorber mass which is free to elongate in a direction reducing its effectiveness as an energy absorber. Even in those applications in which the energy absorbing lead core is surrounded by a resilient support pad having sandwich construction, the degree of confinement is dependent on the magnitude of the vertical load, the elastomer hardness and the thickness of the individual layers of elastomer.

e ~r -4- Specifically, the performance of the lead core may degrade if the vertical load is less than 0.4 times the rated load of the support pad at 0.5 shear strain for an elastomer hardness index between 50 and 55 and an elastomer i~',er thickness of 0.5 inches.

It is the object of this invention to provide an improved cyclic shear energy absorber in which this diminution in performance is minimised.

Summary of the Invention The invention comprises an improved cyclic shear energy absorber which has an extended useful like over known energy absorbers and provides the energy absorbing advantages of the basic device.

In its broadest scope, the invention comprises a cyclic shear energy absorber for absorbing energy due to induced motion between two members, the energy o absorber including first and second coupling means adapted to be coupled to first oo e 3" and second members, such as a support column for a building and a support piling, a plastically cyclically deformable energy absorber means coupled between the first and second coupling means, and a restraining means disposed about the energy absorber means in the region between the first and second coupling means. The restraining means has a flexible wall surface formed by layers for confining the energy absorber means during induced motion between the two members while N permitting the energy absorber means to physically deform in the desired fashion.

The flexible wall surface is provided with some resilience by providing resilient layers between adjacent layers of the flexible wall surface to absorb vertical components of force while still confining the energy absorbing means. Thus the preferred restraining means comprises a flat member generally spirally wound about the outer surface of the energy absorber means, the flexible wall surface being afforded by the individual winding layers each separated from adjacent layors by 0 0 00 V 000 ~-f i i resilient material.

The restraining means is preferably surrounded by a resilient support arranged between the first and second coupling means, the resilient support preferably comprising alternate layers of a resilient material such as rubber and a stiffener material, such as steel, aluminium or fibreglass.

In the preferred geometry, the energy absorbing means comprises a cylindrical core captured between the facing surfaces of the first and second coupling means, the restraining means is a helically wound flat spiral, and .o the resilient support comprises rectangular or square 8040 layers of rubber and steel having a cylindrical aperture o° through the centre for receiving the restraining means and 0 .0 15 the core.

4 O The invention is fabricated by assembling the D 0 resilient support, inserting the restraining means preferably with the aid of a guide fi.tuce, such as a mandrel having a diameter substantially equal to the G o o 20 desived inner diameter of the restraining means, and placing the energy absorber core within the restraininmeans by either press fitting the core into the hollow interior of the restraining means or by casting the core into the interior of the restraining means.

25 In use, when the two coupling means are subjected to o oo vibrations causing lateral displacement, the resilient support, restraining means and energy absorbing core follow this motion. The restraining means permits the energy absorbing core to plastically deform while at the same time confining the core in such a manner as to avoid any excessive mechanical abrading of the core materia..

For a fuller understanding of the nature and advantages of the invention, reference should be had to the ensuing detailed description taken in conjunction with the accompanying drawings.

_i j I I_ 1 Brief Description of the Drawings Figures 1 to 6 relate to preferred embodiments of the parent invention described and claimed in Australian Patent specification 557911.

Figures 7 and 8 relate to two preferred embodiments of the present invention in which: SFigure 7 is a sectional view similar to Figure 2 illustrating an alternative I embodiment of the invention; and I Figure 8 is a sectional view similar to Figure 7 illustrating a still further embodiment of the invention.

Description of the Preferred Embodiments j Turning now to the drawings, Figure 1 illustrates a preferred embodiment of C the parent invention in perspective. As seen in this figure, the energy absorbing SI device includes a central energy absorbing core 2 having a cylindrical shape, a flexible restraining means 3 surrounding the core 2, a resilient support 4 and top t r and bottom coupling plates 7, 8 respectively.

As best seen in Figure 2, the resilient support pad 4 has a sandwich like construction consisting of alternative layers of a resilient material 5, preferably an j elastomeric material such as natural or synthetic rubber, 1f a I ;T 7 and stiffener plates 6 preferably fabricated from steel, aluminium, fibreglass, fabric or other suitable stiffener materials. Resilient support 4 functions as a bearing pad for transferring vertical loads through the device, support 4 is typically mounted between the bottom of a vertical support beam, attached to or resting on the upper plate 7, and a support piling, attached to or engaged with bottom plate 8. The individual layers 5, 6 are typically bonded to one another to forfi a unitary structure, most commonly by vulcanization.

The restraining element 3 is preferably a spirally wound cylindrical structure made from a suitable strip 020 material having a rectangular cross-section. Suitable materials comprise spring steel, mild steel, aluminium 15 strip and any other material capable of being wound to the S* spiral shape shown.

The energy absorbing core 2 is preferably fabricated from high quality lead formed to the cylindrical shape Sillustrated. The term high quality lead is meant to imply 20 lead ha.ving a purity of 99.9%. In many applications, lead having a slightly lower purity, down to about 98% may be

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4 C employed. Other suitable materials are those noted in the above referenced U.S. Patent No. 4,117,637 and any equivalents having comparable cyclic plastic deformation o C 25 characteristics.

The device shown in Figures 1 and 2 is preferably Sfabricated in the following manner. Resilient support 4 is first constructed by forming the individual elements to the square shape illi-trated, or some other suitable geometrical configuration, with the central circular apertures aligned to form a cylindrical void generally at the centre of the support 4. Thereafter, the restraining element 3 is inserted into this aperture, preferably with the aid of a cylindrical mandrel. Thereafter, the energy absorbing core 2 is press fitted into the interior of the I II-a restraining element, after which the top and bottom plates are arranged as shown. It has been found that best results are obtained, when using high quality lead for the energy absorber element 2, by first casting the cylindrical absorber and then press fitting the absorber into the restraining element 3. The size of the cylindrical absorber element 2 should be slightly undersized along the outer diameter with respect to the inner diameter of the element 3 so that the absorber element 2 provides a sliding fit with the interior surface of the restraining element 3. In addition, the 0o0. cylindrical absorber element 2 should be slightly longer than the axial length of the completed device. When casting the energy absorber element 2, the inner diameter 15 of the mould should be essentially the same as the inner 20 diameter of the cylindrical aperture formed in the resilient support 4.

If desired, the energy absorber core element 2 may be aOO4 i° cast in place within the cylindrical volume of the SoOoo 20 restraining element 3, if desired. When employing this alternative method of fabricating the device, the thermal expansivity of lead must be taken into account when pouring the molten core to assure that shrinkage of the core during the subsequent cooling does not result in *s 25 excessive voids between the outer surface of the core element 2 and the inner surface of the restraining element 3. For best results care should be taken to ensure that core element 2 is totally confined on all surfaces, i.e. about the cylindrical side wall surface and on the top and bottom surfaces.

In operation, the device is installed between a support member for a structure, such as a bridge or a building and a base, such as a foundation pad, When a structure is subject to induced vibrations from an earthquake, high winds or the like, which result in shear I I -9forces transmitted to the energy absorber device, the device is subjected to these shear forces and distorts in the manner illustrated in Figure 3. As seen in this figure, the core element 2 has deformed from its normal right circular cylindrical shape in response to the shear forces, and the restraining element 3 follows the same motion. Due to the rectangular cross-sectional configuration of the restraining element 3, adjacent layer windings are slidably translated from their normal vertical alignment illustrated in Figure 2 to the 'pdisplaced configuration shown in Figure 3. However, rr C sufficient surface area exists between adjacent layers to provide vertical support to prevent collapse of the restraining element 3, or distortion of this element, in 15 combination with the surrounding resilient layers 5, so that the core element 2 retains its generally cylindrical outline, even though the cylinder is skewed from the vertical. In addition, the flexibility of the wall S surface afforded by the inner surfaces of the individual ,o 20 winding layers of restraining element 3 and the slidable arrangement for the adjacent layers, permits the core 9 o element 2 to deform sufficiently to dissipate energy while preserving the integrity of the core element. As noted above, most of the energy is dissipated by heat generated 25 in the core element 2, while the remaining energy is stored in both the element 2 and the resilient support 4.

This stored energy is used to return the material of the core to its original mechanical state. In addition, release of that portion of the energy stored in the resilient support 4 will tend to return core element 2 to its ortginal geometrical configuration illustrated in Figure 2.

Actual tests conducted on energy absorber devices fabricated according to the teachings of the parent invention have shown that the useful lifetime of the 1 i ii 1111- -CICI 10 improved energy absorber device is much greater than a similar device constructed according to the prior art but lacking the restraining element 3.

Specifically, the results of a research programme recently completed at the University of Auckland in New Zealand, are described in the following publications: Reference 1. King, P.G. "Mechanical energy dissipators for 0096 0 **0 o C.

eloo eq seo G o e o o* 001 9 a 0 0 0 0O «0 *0 2. Buint, S.M.

seismic structures", Department of Civil Engineering Report No. 228, University of Auckland, August 1980.

"Lead-rubber dissipators for the base isolation of bridge structures", Department of Civil Engineering Report No. 289, University of Auckland, August Ii 1982.

To summarize the results, twenty 15 inch x 12 inch x 4 inch lead filled elastomeric bearings with 5, one-half inch internal layers, were dynamically tested for a wide 20 range of vertical loads and shear strain amplitudes. Five cycles of displacement were imposed to each of combinations of vertical load and shear strain.

Dissipated energy was measured from the area of the load deflection hysteresis loops together with the S characteristic yield strengths, and the elastic and post-elastic stiffnesses. Various unconfined lead configurations were investigated and the results compared with tests on lead cylinders confined in the manner described above. Built (1982) describes the results of the particular tests where it is typically shown that the energy dissipated per cycle was more than doubled when the lead cylinder was confined.

In many applications, the frictional force between the lower surface of upper plate 7 and the abutting surface of upper layer 5, and the frictional force between 11 the upper surface of lower plate 8 and the abutting surface of adjacent resilient layer 5 are sufficient to provide the shearing action described above and partially illustrated in Figure 3. In some applications, it may be desirable to provide additional couplinq between the plates 7, 8 and the interposed resilient support 4. One technique for *roviding this additional coupling comprises bonding the plates 7, 8 to the end surfaces of the resilient support 4, e.g. by vulcanization, adhesives or the like. In other applications, it may be desirable to provide additional engagement between the plates 7, 8 and the resilient support 4. Figure 4 illustrates a first alternate embodiment of the parent invention in which a positive engagement force is provided between the plates 7, 8 and the resilient support 4. As seen in this figure, the lower surface of upper plate 7 is provided with an abutment collar 11 having the same geometrical configuration as the outer perimeter of resilient °oo" S support 4 (shown as rectangular in Figure Collar 11 eO O 20 is configured and dimensioned in such a manner that the uppermost portion of resilient support 4 can be received within the collar 11 when plate 7 is lowered into the resilient support 4. Bottom plate 8 is provided with a similar abutment collar 12 on the upper surface thereof, 25 collar 12 being dimensioned and configured substantially identical with collar 11. In use, lateral displacement between plates 7 and 8 is transmitted to the resilient support 4 not only by the frictional forces betwsn plates 7, 8 and the support 4 but also positively li means of the mechanical force between the collars 11, 12 and the support 4. Collars 11, 12 may be secured to plates 7, 8 in any suitable fashion, such as welding, brazing, adhering or the like.

Figures 5 and 6 illustrate an alternate embodiment of the parent invention also providing a positive engagement i wxl-~~Y~ 12 *e o an 4 4* ase *0 0 00 0 a e Sa between the plates 7, 8 and the resilient support 4. As seen in these figures, upper plate 7 is provided with a plurality of downwardly depending dowel pins 13 arranged in a predetermined pattern, illustrated as a circular pattern of four pins 13 spaced by 900 about the centre axis of the core element 2. A corresponding plurality of apertures 14 are similarly preformed in the upper most resilient layer 5 and the upper most stiffener plate 6.

The apertures 14 may extend entirely through the upper most stiffenor plate 6 or only partially through the plate. The arranuom'ent of the pins 13 and the apertures 14 is such that the pins 13 may be pressed down into the apertures 14 as the top plate 7 is lowered onto the resilient support 4. Lower plate 8 is provided with a 15 similar arrangement of dowel pins 15, and lower most resilient layer 5 and lower most stiffener plate 6 are provided with corresponding apertures 16.

Although the preferred embodiments have been illustrated as preferably incorporating upper and lower 20 plates 7, 8 in some applications these plates may be incorporated into the associated structural members, or the function of the plates 7, 8 may be provided by surfaces defined by the associated structural members.

For example, lower plate 8 may comprise the upper surface of a concrete support pad for a power plant, while upper plate 7 may be the bottom of the containment housing for the power plant. Other variations will occur to those skilled in the art.

While the above provides a full and complete 30 disclosure of the preferred embodiment of the parent invention, various modifications, alternate constructions and equivalents may be employed without departing from the true spirit and scope of the parent invention. For example, while right circular cylindrical geometry has been specifically described for the preferred embodiment,

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a. a a *ea 1- I !t 13 other geometries may be employed, such as rectangular, trapezoidal, elliptical, and the like. Further, while the resilient support 4 has been disclosed as having rectangular geometry, other geometrical configurations may be used for this compound element as well, including circular geometry. In addition, while the restraining element has been des ribed with references to a flat spirally wound cylinder, other configurations may be employed, depending on the geometry of the core element 2. For example, if a rectangular core element is employed, the restraining element will have a similar rs I rectangular geometry. Moreover, if deaired the restraining element may comprise individual elements (circular flat rings, rectangular flat frames, or the qmw S 15 like) arranged in a vertical stack.

oThe embodiments illustrated in Figures 1 to 6 incorporate an element 3 which shall be referred to hereafter as a closed helix. In this embodiment each turn is in physical contact with its neighbour. This suffers r* 20 the disadvantage that the bearing is made vertically rigid in the vertical direction and manufacturing by the pressing in place method can cause severe damage to the helix. In order to avoid such a disadvantage an alternative construction illustrated in Figures 7 and 8 25 have been made. In each of these constructions the lead core 2 is surrounded by a confining element but the element has a certain amount of compressibility in a vertical direction.

In the embodiment illustrated in Figure 7 a helical coil 3 is surrounded by an elastomer 17 such as urethane or silicon rubber. In a preferred embodiment this is constructed by a hose manufacturer using a technique known for the production of hydraul)- suction hose.

The inclusion of the elastul, ric material 17 between the individual windings 3 of the helix provides an 14open-helix stracture whici. does not have the disadvantages outlined above for the closed helix.

In a still further embodiment illustrated in Figure 8 a bearing 1 comprises a cylindrical lead core 2 and end plates 7 and 8. All except for the ends of the lead core 2 are surrounded by elastomeric material 5. In this embodiment an open helix 3 is wound around the lead core alternating with shims or stiffener plates 6 and elastomer 5 provides layers between the turns of the helix 3 and the individual shims or stiffener olates 6.

Helix 3 is separated into its individual turns in this a embodiment.

In both Figure 7 and Figure 8 as an alternative to a continuous helix 3 or separated helix portions 3 annular 15 rings separated by elastomeric material may be employed.

*e0l It has been observed in operation that the provision of the elastomeric material between the layers of the helix are layers of annular material does not e'fect the ability to confine the lead core to provide the advantages 20 outlined above with reference to Figures 1 to 6.

Similarly other geometric configuration and •a arrangements discussed in relation to the embodiments of Figures 1 to 6 are equally applicable with respect to Figures 7 and 8. Therefore, the above description and illustrations should not be construed as limiting the scope of the invention, which is defined by the appended claims.

Claims (19)

1. In a cyclic shear energy absorber adapted to be interposed between two members for absorbing energy due to induced motion between said two members, said energy absorber including a first end portion adopted to be coupled to one of said two members, a second end portion adapted to be coupled to the other one of said two members, plastically cyclically deformable energy absorber means extending between said first and second end portions, and restraining means disposed about said energy absorber means in the region between said first and second portions, said restraining means having a flexible wall surface for confining said energy absorber means during induced motion between said two members while permitting said energy absorber means to deform, the improvement t comprising the provision of resilient layers between adjacent layers of said flexible i 1i* wall surface in said restraining means. ,4 t

2. The improvement of claim 1 wherein said restraining means comprises a flat i member generally spirally wound about the outer surface of said energy absorber means, said flexible wall surface being formed by the individual winding layers each separated from adjacent layers by said resilient layers.

3. The improvement of claim 1 further including a resilient support surrounding 9 i said restraining means and arranged between said first and second end portions.

4. The improvement of claim 3 wherein said resilient support comprises alternative layers of resilient material and stiffener material. The improvement of claim 4 wherein said restraining means comprises alternating layers of said resilient material, spirally wound flat members and said stiffener material.

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6. The improvement of claim 1 wherein said energy absorber means comprises a lead core.

7. The improvement of claim 1, further including an upper plate member coupled to said first end portion and a lower plate member coupled to said second end portion.

8. The improvement of claim 3 further including an upper plate member coupled to said first end portion and a lower plate member coupled to said second end portion, and wherein at least one of said upper and lower plate members includes abutment means for transferring forces between said plate member and the associated end portion.

9. The improvement of claim 8 wherein said first end portion and said second end portion each has a rectangular perimeter and said abutment means comprises a rectangular shoulder surrounding said perimeter.

The improvement of claim 5 further including an upper plate member coupled to said first end portion and a lower plate member coupled to said second end portion, and wherein at least one of said upper and lower plate members includes abutment means for transferring forces between said plate member and said energy absorber means, and a resilient support having a plurality of longitudinally extending apertures formed therein extending from the end portion thereof adjacent at least one plate member, and said abutment means comprising a corresponding plurality of dowel members each received in an associated one of said plurality of apertures.

11. A cyclic shear energy absorber for absorbing energy due to induced motion between two members, said energy absorber comprising; to -17- first coupling means adapted to be coupled to a first one of said two members; second coupling means adapted to be coupled to the other one of said two members; plastically cyclically deformable energy absorber means coupled between said first and second coupling means; and restraining means disposed about said energy absorber means in the region between said first and second coupling means, said restraining means having a flexible wall surface for confining said energy absorber means during induced motion between said first and. second coupling means while permitting said energy absorber to deform, said flexible wall surface comprising resilient layers between adjacent layers of said flexible wall surface.

12. The cyclic shear energy absorber of claim 11 wherein said restraining means comprises a flat member generally spirally wound about the outer surface of said energy absorber means, said flexible wall surface being formed by the individual winding layers each separated from the adjacent layers by said resilient layers.

13. The cyclic shear energy absorber of claim 12 wherein said flat member is ,fabricated from spring steel. t

14. The cyclic shear energy absorber of claim 13 wherein said flat member is c fabricated from aluminium. The cyclic shear energy abs:- 'ber of claim 11 further including a resilient support surrounding said restraining means and arranged between said first and second coupling means.

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16. The cyclic shear energy absorber of claim 15 wherein said first and second ,o0 -18- coupling means each includes abutment means for transferring forces to said resilient support.

17. The cyclic shear energy absorber of claim 16 wherein said abutments means comprises a shoulder in contact with the outer periphery of said resilient support.

18. The cyclic shear energy absorber of claim 15 wherein said resilient support comprises alternate layers of resilient material and stiffener material.

19. The cycle shear energy absorber of claim 18 wherein said restraining means comprises alternating layers of said resilient material, spirally wound flat members and said stiffener material. The cyclic shear energy absorber of claim 19 wherein said resilient support is provided with a first plurality of apertures extending from the upper surface thereof downwardly into the uppermost layer of stiffener material and a second nno plurality of apertures extending from the lower surface thereof upwardly into the .lower most layer of stiffener material, and wherein said abutment means includes 6 a first plurality of dowel members extending downwardly from said first cor;pling means with each of said dowel members receiving in a corresponding one of said first plurality of apertures and a second plurality of dowel members extending upwardly from said second coupling means with each of said second plurality of to, t dowel members receiving in a corresponding one of said second plurality of oapertures. 4 21. The cyclic shear energy absorber of claim 10 wherein said energy absorber means comprises a lead core. DATED this 25th day of NOVEMBER 1991 r -19- DEVELOPMENT FINANCE CORPORATION OF NEW ZEALAND Patent Attorneys for the Applicant: F.B. RICE CO. 44r~ 4 4: 4 t 4~~c 1I Ii 4