CA1243696A - Energy absorbers - Google Patents

Abstract

ABSTRACT

A cyclic shear energy absorber for absorbing energy due to induced motion between two members by plastic cyclical deformation of a central energy absorber core. The core is surrounded by a restraining device having a rectangular cross-section. Layers of the inner walls are separated by layers of resilient material. The restraining element is confined in a cylindrical aperture formed in a resilient support having alternating resilient layers and stiffener layers. The absorber is confined beween two end plates capable of being coupled to associated structural members, such as a bridge support column and a base.

Description

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~ackaround of the Invention Thls invention relates to energy absorbers used In conJunctlon with large structures to reduce the tnfluence of externally Induced motlon on such structures. Thls Is a contlnuatlon~ln-part of Unl~èd States Patent 4,499,694. The Inven-i-lon clalmed tn IJ.S. Pateni 4,499,694 Ts referred to hereln as the parent Inventlon.
Cycllc shear energy absorblng devlces are known whlch employ the cycllc plastic deforma-tlon of certaln materlals beyond the elastlc llmlt for the absorptlon of klnetic energy. Such absorblng devlces are typlcally Interposed between a bulldlng support member and a base member, or between two structural support members, In order to convert portlons of the klnetic energy Into heat In the absorblng materlal and thus reduce the motion Imparted to the structure by externally Induced forces, such as an earthquake or hlgh wlnds. U.S. Patent No. 4,117,637 issued October 3, 1978, to Roblnson for "Cyclic Shear Energy Absorber"~

Illustrates several geometrical configuratlons of the basic cycllc shear energy absorber devlce. The baslc device includes a palr of spaced coupllng members, typlcally plates, each one of whlch Is deslgned to be coupled to an Indlvldual structural member. When used In a bullding envlronmentJ for example, one of the coupllng members Is conflgured to be attached to a support plllng, while the other coupllng member Is conflgured to be attached to a support plllar, beam or the llke. Arranged between the two couplIng members Is a solid plastlcally cyclIcally deformable mass of materlal, typlcally lead, which provides the energy absorptlon functlon. Some conflgurations of this type of devlce further 1nclude an addltlonal reslllent pad structure whlch ' ~ ~

surrounds the energy absorbing mass and provides reslllent vertlcal support between the -~wo coupling members, usually by means of a sandwich comprising alternate layers of a resll1ent material (e,g.
rubber) and a stlffener material (e.g. steel, alumlnlum or the llke).
In use, when externally Induced forces result In relatlve lateral motlon between the two couplIng members, the solId energy absorblng mass Is cycled beyond Its elastlc llmlt, converting some of the energy Into heat and storlng the remalnlng energy when the mass Is In the deformed state, the latter actlng as a drlvlng force which tends to lo return the materlal to Its orlglnal mechanlcal propertles. As a consequence, the energy transmltted to or through the structure is converted Into heat rather than belng applied In a destructlve fashlon to the bullding. Consequently, structures Incorporatlng such absorbers have a hlgher safety factor than those relylng on the ductlle behavlour of structural members to dlsslpate energy (which wlll be damaged by a severe earthquake and wlll be dlf f i CU It to repalr or replace), and those uslng rubber dampers, (which functTon In a sprlng llke fashion and dlsslpate only small amounts of externally Imparted energy).
Whlle cycllc energy absorbers of the above type have been found to functlon well In many appllcatlons, In some applications premature degradatlon of the energy absorblng mass occurs after a small number of osclllatlons has been-observed.
Thls Is due to a lack of conflnement about the absorber mass whlch Is free to elongate In a dtrectlon normal to that of the tmposed deformatlon and thereby reduclng Its effectlveness as an energy absorber. Even tn those applIcatlons In whlch the energy absorblng lead core Is surrounded by a reslllent support pad havlng sandwlch constructlon, the degree of confInement ts dependent on the magnltude "

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of the vertical load, the elastomer hardness and the thlc~ness of the indivldual layers of elastomer. SpeclfIcally, the performance of the lead core may degrade If the vertlcal load Is less than 0.4 tlmes the rated load of the support pad a-f 0.5 shear stratn for an elastomer hardness Index between 50 and 55 and an elastomer layer thIckness of 0.5 Inches.
It Is the obJect of thls Inventlon to provlde an improved cyclic shear energy absorber in which this dimlnutlon Tn performance ts substantially reduced or whlch at least offers the public a useful lo choiceO

Summary of the Inyentlon The Invention comprlses an improved cycilc shear energy absorber whlch has an extended useful llfe over known energy absorbers and provides the energy absorblng advantages of the baslc devlce.
In its broadest scope, the inventlon comprlses a cycllc shear energy absorber for absorblng energy due to Inciuced motlon between two members, the energy absorber Includlng flrst and second coupllng means adapted to be coupled to fIrst and second members, such as a suppor-i-column for a bulIding and a support plllng, a plastlcally cyclTcally deformable energy absorber means coupled between the flrst and second coupilng means, and a restralning means dlsposed about the energy absorber means In the reglon between the flrst and second coupllng means. The restralnlng means has a flexible wall surface for conflnlng the energy absorber means durlng induced motlon between the two members whlle permlttlng the energy absorber means to physlcally deform In the deslred fashlon. The flexlble wall surface Is provlded wlth some reslllence to absorb vertlcal components of force whlle stlll conflnlng ~ .
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the energy absorbing means. in a preferred embodtment of the Invention, the restralnlng means comprises a flat member generally spirally wound about the outer surface of the energy absorber means, the flexible wall surface belng afforded by the indlvldual wlndlng layers at least some of which are separated from adJacsl1t lay~rs by reslllen1 materlal.
In another preferred embodlment the restralnlng means comprlsss a serles of flat members generally surroundlng the outer surface of the energy absorber, at least some of the flat members being separated from their adJacent members by reslllent materlal.
The restrainlng means is preferably surrounded by a restllent support arranged between the fIrst and second couplIng msans, the reslllent support preferably comprislng alternate layers of a reslllent matertal such as rubber and a stlffener material, such as steel, aluminlum or fibreglass.
In the preferred geometry, the energy absorblng means CGmprlses a cylindrlcal core captured between the faclng surfaces of the flrs-t and second coupllng means, Ihe restralnlng means Is a hellcally wound flat splral, and the reslllent support comprlses rectangular or square layers of rubber and steel havlng a cyllndrlcal aperture through the centre for recelvlng the restralnlng means and the core.
The tnventlon Is fabrlcated by assembllng the restllent support, Insertlng the restralnlng means preferably wlth the ald o~ a gulde flxture, such as a mandrel havlng a dlameter substantlally equal to the deslred Inner dlameter of the restralnlng means, and placlng the energy absorber core wlthin the restralning means by elther press fltting the core Into the hollow Interlor of the restralnlng means or by castlng the core Into the Interlor of the restraining means.
In one embodlment the absorber has end plates and the assembly Is .: .

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-held together by vulcanlza-tion, coupllng or the 11ke. A hole Is provided in one end plate allgned with the cylIndrlcal energy absorblng core. The hole Is threaded. An end cap which Is also threaded is screwed in-to the hole to compress the core.
In use, when the two coupling means are subjected to vibratlons causlng lateral dlsplacement, the reslllen~ support, restralnlng means and energy absorblng core follow -this motlon. The restralnlng means permits the eneryy absorblng core to plastlcally deform whlle at the same tlme conflnlng the core In such a manner as to avold any excesslve lo mechanlcal abradlng of the core materlal.
For a fuller understandlng of the nature and advantages of the Inventlon, reference should be had to the ensulng detalled descrtptlon taken In conjunctlon wlth the accompanying drawlngs.

Brief Descrlption of the Drawlnqs Flgure 1 Is a perspectlve vlew of a preferred embodlment of the parent Inventlon;
Flgure 2 1s a sectlonal vlew taken along line 2-2 of Flgure 1;
Flgure 3 Is an enlarged dlagrammatic sectlonal vlew Illustratlng operatlon of the restralnlng means;
Flgure 4 Is a sectlonal vlew slmllar to Flgure 2 tllustratlng an alternatlve embodlment of the parent Inventton;
Flgure 5 Is a sectlonal vlew slmtlar to Ftgure 4 Illustra-ttng another alternatlve embodlment of the parent Inventlon; and Flgure 6 Is a plan vlew taken along Itne 6-6 of Flgure 5.
Flgures 7, 8 and 9 relate to two preferred embodtments of the present Inventlon In whlch:
Flgure 7 Is a secttonal vlew slmllar to Flgure 2 tllustrating an , alternatlve embodiment of the Inventlon; and Figure 8 is a sectional view slmilar to Figure 7 Illustratlng a still further embodiment of the inventlon.
Figure 9 ts a sectional view slmllar to Figure 8 Illustratlng a stlll furth~r embodlment of the Invention.
The embodlments of Figures 1 to 6 may be modlfled by the Insertlon of reslllent materlal between at least some adJacent layers of -ihe restrainlng member so as to incorporate the distlngutshlng feature of the present Inventlon.

DesçrTptlon of ~he Prefqrred Em~Q5lm~n~

Turning now to the drawings, Flgure 1 Illustrates a preferred embodlment of the parent tnventton In perspective. As seen in thls f7gure, the energy absorblng devlce Includes a central energy absorbing core 2 having a cylindrlcal shape9 a flexible restralnlng means 3 surroundlng the core 2, a reslllent support 4 and top and bottom coupllng plates 7, 8 respectively.
As best seen In Flgure 2, the resllient support pad 4 has a sandwlch llke constructlon consistlng o~ alternatlng layers of a reslllent materlal 5, preferably an elastomeric materlal such as natural or synthettc rubber, and stlffener plates 6 preferably fabrlcated from steel, alumlnlum, flbreglass, fabrlc ar other sultable stl~fener materlals. Reslllent support 4 functlons as a bearlng pad for transferrlng vertlcal loads through the device, and support 4 Is~
typlcally mounted between the bottom of a vertlcal support beam, attached to or engaged wlth bottom plate 8. The Individual layers 5~ 6 are typically bonded to one another to form a unltary structure, mosf commonly by vulcanl~atlon.

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The restralning element 3 is preferably a 5p Iraily wound cylIndrical structure made From a suitable strip material having a rectangular cross sectlon. Sultable materlals comprlse sprlng steel, mild steel, alumlnium strip and any other materlal capable of belng wound to the splral shape shown.
The energy absorblng core 2 Is preferably fabrlcated from hlgh quallty lead formed to the cyllndrlcal shape Illustrated. The i-erm hlgh qualIty lead Is meant to Imply lead havlng a purity of 99.9~. In many applicatlons, lead having a slightly lower purfty, down to abouf lo 98~ may be employed. Other sultable materials are those noted In the above referenced U.S. Patent No. 4,117,637 and any equivalents havlng comparable cycllc plastlc deformatton characterlstlcs.
The devlce shown In Flgures 1 and 2 is preferably fabricated In the followlng manner. Reslllent support 4 Is first constructed by formlng the Indlvldual elements to the square shape Illustrated, or some other suitable geometrlcal conflguration~ wlth the central clrcular apertures allgned to form a cylindrlcal voTd generally at the centre of the support 4. Thereafter, the restralnlng element 3 Is inserted Into thls aperture, preferably with the ald of a cyllndrlcal mandrel. Thereafter, the energy absorblng core 2 Is press fltted Into the Interlor of the restralnlng element, after whTch the top and bottom plates are arranged as shown. It has been found that best results are obtalned, when uslng hlgh quality lead for the energy absorber element

2, by flrst castlng the cyllndrlcal absorber and then press fittlng the absorber Into the restralnlng element 3. The slze of the cyllndrlcal absorber element 2 should be sllghtly underslzed along the outer dlameter with respect to the Inner dlameter of the element 3 so ~hat the absorber element 2 provldes a slidlng fIt wlth the Interior surface of the restralnlng element 3. In addltlon, the cyllndrlcal absorber .. ' ' .

8 ~ 6~6 element 2 should be sllghtly longer than the axlal length of the completed device. When castlng the energy absorber element 2, the Inner diameter of the mould should be essentlally the same as the Inner dlameter of the cylindrlcal aperture formed In the reslllen~ suppor-f ~.
If deslred, the energy absorber core ele~ent Z may bc cast in place wlthln the cylIndrlcal volume of the restrainlng element 3. ~hen employing thls alternatlve method of fabrlcating -the devlce, the thermal expanslvlty of lead must be taken Into account when pourlng the molten core to assure that shrlnkage of the core durlng the subsequent lo coollng does not result Tn excesslve volds between the outer surface of the core element 2 and the Inner surface of the restralnlng 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 cyllndr1cal slde wall surface and on the top and bottom surfaces.
In operation, the devlce Is Installed befween a support member for a structure, such as a brldge or a bulldlng and a base/ such as a foundatlon pad. When a structure Is subjected to Induced vlbrations from an earthquake, hlgh winds or the llke, whlch result In shear forces transmltted to the energy absorber device, the dev3ce Ts subJected to these shear forces and dlstorts In the manner Illustrated In Figure 3. As seen In this Figure, the core element 2 has deformed from Its normal rlght clrcular cyllndrlcal shape In response to the ~shear forces, and the restralnlng element 3 follows the same motion.
Due to the rectangular cross-sectional conflguratlon of the restralnlng element 3, adJacent layer wlndlngs are slIdably translated from thelr normal vertlcal alignment Illustrated In Flgure 2 to the dlsplaced conflguratlon shown In Flgure 3. However, suffIclent surface area exlsts between adJacent layers to provlde vertlcal support to prevent collapse of the restralnlng element 3, or dls~ortlon of thTs elemen~

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in comblnation wlth the surroundtng reslllent layers 5, so that the core element 2 retalns its generally cylIndrical outlIne, even though the cylinder Is skewed from the vertical. In addltlon, the flexlblllty of the wall surfacs afforded by the Inner surfaces of ~he Indlvldual wlndlng layers of restralnlng element 3 and ihe slldable atrangement for the adJacent layers, permlts the core element 2 ~o deform sufflclently to dlsslpate energy whlle preserv1ng the Integrlty of the core element. As noted above, most of the energy Is dlsslpated by heat generated In the core element 2, while the remalnlng energy Is stored lo 1n both the element 2 and the reslllent support 4. Thls s-tored energy Is used to return the mater1al of the core to Its ortg1nal mechanlcal state. In addltton, release of that portlon of the energy stored In the resllient support 4 wlll tend to return core element 2 to Its orlgtnal geometrlcal conflguratlon Illustrated In Flgure 2.
Actual tests conducted on energy absorber devlces fabrlcated accordlng to the teachlngs of the parent Inventlon have shown that the useful lifetlme of the Improved energy absorber devlce Is much greater than a slmilar devlce constructed accordlng to the prlor art but lacklng the restralnlng element 3.
Speclflcally, the results of a research programme conducted at the Untversity of Auckland In New ~ealand, are described In the followlng publIcatlons:
Reference 1. Klng, P~Go "Mechanlcal energy dlsslpators for selsmlc structures", Department of Clvll Englneerlng Report No. 228, Unlverslty of Auckland, ~ugust 1980.
2. Bullt, S.M. "Lead-rubber dlsslpators for the base Isolatlon of brldge structures", Department of Civil Englneerlng Report No. 289, Unlverslty of Auck lan~) August 1982.

l o To summarize the results, twenty 15 inch x 12 Inch x 4 Inch lead fllled elastomerlc bearlngs wlth 5, one-half Inch internal layers, were dynamlcally tested for a wide range of vertlcal loads and shear straln amplltudes. Flve cycles of dlsplacement were Imposed to each of 25 combinatlons of vertlcal load and shear straln. Dlsslpated energy was measured from the area of the load deflectlon hysteresls loops together wlth the characterlstlc yleld strengths, and the elastlc and post-elastlc stlffnesses. Varlous unconflned lead conflguratlons were investlgated and the result~ compared wlth tests on !ead cyllnders lo confIned In the manner descrlbed above. BulIt (1982) descrlbes the results of the partlcular tests where it Is typlcally shown that the energy dissipated per cycle was more than doubled wnen the lead cylinder was conflned.
In many applIcations, the frlcttonal force between the lower surface of upper plate 7 and the abutting surface of upper layer 5, and the frlctlonal force between the upper surface of lower plate 8 and the abutting surface of adJacent restl1ent layer 5 are sufficlent to provlde the shearing actlon descrtbed above and partlally illustrated tn Flgure 3. In some applIcatlons, It may be deslrable to provlde addltlonal c~uplIng between the plates 7, 8 and the Interposed reslllent support 4. One technlque for provldlng thls addltlonal coupllng comprlses bondlng the plates 7, 8 to the end surfaces of the reslllent support 4, e.g. by vulcanlzatlon, adheslves or the Itke. In other applIcatlons, tt may be deslrable to provlde addltional engagement between the plates 7, 8 and the restllent support 4. Flgure 4 Illustrates a flrst alternate embodlment of the parent 1nventlon In whlch a poslt1ve engagement force Is provlded between the plates 7, 8 and the reslllent support 4. As seen In this flgure, ~he iower surface of upper plate 7 Is provided wlth an abutment collar 11 havlng the same , . .

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geometrical conflguratlon as the outer perlmeter of resll1ent support 4 (shown as rec-~angular In Figure 1). Collar 11 is conflgured and dlmensioned Tn such manner that the upper most portton of reslllent support 4 can be received wlthtn the coilar 11 when plate 7 Is lowered into the reslllent support 4. Bottom plate 8 is provtded wlth a slmllar abutment collar 12 on the upper surface thereo~, collar lZ
being dtmensioned and conflgured substantlally Identlcal wlth collar 11. In use, lateral displacement between plates 7 and 8 Is transmltted to the reslllen-t support 4 not only by the frlct10nal forces between o plates 7, 8 and the support 4 but also posltlvely by means of the mechanlcal force between the collars 11, 12 and the support 4. Collars 11, 12 may be secured to plates 7, 8 in any suitai~le fashlon, such as by weldlng, braztng, adhering or the llke.
Flgures 5 and 6 illustrate an alternatve embodiment of the parent inventlon also providlng a posltlve engagement between the plates 7, 8 and the reslllent support 4. As seen in these flgures, upper plate 7 Ts provlded wlth a pluralIty of downwardly depending dowel p1ns 13 arranged in a predetermined pattern, illustrated as a clrcular pattern of four plns 13 spaced by 90 about the centre axls of the core eiement 2. A correspondlng pluralIty of apertures 14 are slmllarly preformed In the upper most reslllent layer 5 and the upper most stiffener plate 6. The apertures 14 may extend entirely through the upper most stlffener plate 6 or only partlally through the plate. The arrangement of the plns 13 and the apertures 14 Is such that the plns 13 may be pressed down Into the apertures 14 as the top plate 7 ts lowered onto the reslllent support 4. Lower plate 8 Is provlded wlth a slmilar arrangement of dowel plns 15, and lower most reslllent layer 5 and lower most stlffener plate 6 are provided with correspending apertures 16.

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Although the preferred embodlments have been 111ustrated as preferably incorporatlng upper and lower plates 7, 8 in some applIcations these plates may be incorporated Into the associated structural members, or the functlon of the plates 7, 8 may be provlded by surfaces deflned by the associa-i-ed structural members. For ~xample, lower plate 8 may comprlse the upper surface of a concrete support pad for a power plant, while upper plate 7 may be the bottom o~ the containment housing for the power plant. Other variat10ns will occur to those skliled In the art.
lo Whlle the above provldes a full and complete dlsclosure of the preferred embodlment of the parent Inventlon, various modlflcattons, alternate constructlons and equlvalents may be employed without departlng from the true splrlt and scope of the parent Inventlon. For example, whlle rtght circular cyllndrlcal geometry has been spectf1cally descrlbed for the preferred embodlment~ other geometrles may be employed, such as rectangular, trapezoldal, elliptlcal, and the tike. Further, whlle the resll1ent support 4 has been d1sclosed as havlng rectangular geometry, other geometrical conflguratlons may be used for thls compound element as well, Includlng clrcular geometry.
In addltlon, whlle the restralnlng element has been descrlbed wlth references to a flat splrally wound cyllnder, other conflgurations may be employed, depending on the geometry of the core element 2. For example, If a rectangular core element Is employed, the restralnlng element wlll have a slmllar rectangular geometry. Moreover, If deslred the restralnlng element may comprise Indlvldual elements (clrcular flat rlngs, rectangular flat frames, or the llke) arranged In a vertlcal stack.
The embodlments Illustrated 1n Flgures 1 to 6 incorporate an element 3 whlch shall be referred to hereafter as d closed he~1x. In .

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this embodlment each turn Is In physlcai contact wifh Its nelghhour.
Thts suffers the dlsadvantage that the bearlng is made rigld in the vertical direction and manufacturlng by the pressing In place method can cause severe damage to the helix. In order to avold such a dlsadvantage an alternative constructlon lllustrated In F1gures 7 and 8 have been made. In each of these construc-i-lons the lead core 2 Is surrounded by a conflnlng element but the element has a certaln amouni of compresslblllty In a vertlcal dlrec-tlon.
In the embodlment illustrated In Flgure 7 a hellcal coll 3 Is lo surrounded by an elastomer 17 such as urethane or stllcon rubber. In a preferred embodimant thls Is constructed by 3 hose manufacturer uslng a technlque known for the production of hydraullc suctlon hose. The incluslon of the elastomeric materlal 17 between the Indtvidual wlndlngs 3 of the hellx provides an open-hellx structure whlch does not have the dlsadvantages outlined above for the closed hellx.
In a stlll further embodlment Illustrated In Flgure 8 a bearing 1 comprlses a cyllndrlcal lead core 2 and end plates 7 and 8, All except for the ends of the lead core 2 are surrounded by elastomertc materlal 5. In thts embodlment an open hellx 3 is wound around the lead core alternatlng wtth shlms or stlffener plates 6 and elastomer 5 provtdes layers between the turns of the hellx 3 and --he indlYldual sh1ms or stlffener plates 6. Helix 3 Is separated Into Its tndlvldual turns In thls embodlment.
In both Flgure 7 and Figure 8 as an alternat5ve to a continuous hellx 3 or separated hellx portlons 3 stacked rtngs separated by elastomerlc material may be employed.
In all embodlments only some of the elements 3 may be separated from contact with one another provlded there Is some vertlcal restllence In the flexlble wallO

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It has been observed In operation that the provlslon of the elastomeric materlal between the layers of the helix or layers of annular materlal does not effect the abillty of the restraining means to conflne the lead core 2 to provlde the advantages outllned above wlth reference to Flgures 1 to 6.
In Flgure 9 there Is Illus-trated an embodlment comprlslng an upper plate 7, a lower plate 8 and alternatlng layers of elastoMertc materlal 5 and stlffenlng materlal 6. Apertures 9 are provided through plates 7 and 8 to allow them to be attached to structures or bases. A hole correspondlng to the cross-sectlon of core 2 Is provlded through upper plate 7. Thls hole Is Internally threaded. Cap 19 of approprlate diameter Is externally threaded. Cap 19 may be screwed dw n through plate 7 to asslst In the vertical conftnement of core 2. Care has to be taken In tlghtenlng down cap 19 so that plate 7 Is not delamlnated from elastomerlc layer 5. The wetght of a structure on plate 7 wlll ensure thTs once the device Is posltioned under a buildlng.
Slmllarly other geometrlc conflguratlons and arrangements dlscussed In relatlon to the embodlments of Flgures 1 to ~ are equally applIcable wlth respect to Flgures 7, 8 and 9. Therefore, the above descrlptlon and Illustratlons should not be construed as limltlng the scope of the Inventlon, whlch Is deflned by the appended clalms.

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Claims (25)

What is claimed is:

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 engageable to one of said two members, a second end portion engageable 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 comprising the provision of resilient layers between at least some adjacent layers of said flexible wall surface in said restraining means.

2. The improvement of claim 1 wherein said restraining means comprises a flat member generally spirally wound about the outer surface of said energy absorber means.

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

4. The improvement of claim 3 wherein said resilient support comprises alternating layers of resilient material and stiffener material.

5. The improvement of claim 4 wherein said restraining means comprises alternating layers of said resilient material, spirally wound plate members and said stiffener material.

6. The improvement of claim 1 wherein said restraining means comprises a stack of flat members surrounding the outer surface of said energy absorber means, said flexible wall surface being formed by the flat members, at least some of which are separated by said resilient layers.

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

8. 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.

9. 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.

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

11 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.

12. The improvement of claim 11 wherein there is provided a threaded aperture through said upper plate aligned with said energy absorber means and a cap which can be threaded into said aperture to confine said energy absorber means in an axial direction.

13. A cyclic shear energy absorber for absorbing energy due to induced motion between two members, said energy absorber comprising:
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.

14. The combination of claim 13 wherein said restraining means comprises a flat memeber generally sprially wound about the outer surface of said energy absorber means, said flexible wall surface being formed by the individual winding layers at least some of which separated from the adjacent layers by said resilient layers.

15. The combination of claim 13 wherein said restraining means comprises a stack of flat members surrounding the outer surface of said energy absorber means, said flexible wall surface being formed by the flat members, at least some of which are separated by said resilient layers.

16. The combination of claim 14 wherein said flat member is fabricated from spring steel.

17. The combination of claim 16 wherein said flat member is fabricated from aluminium.

18. The combination of claim 13 further including a resilient support surrounding said restraining means and arranged between said first and second coupling means.

19. The combination of claim 18 wherein said first and second coupling means each includes abutment means for transferring forces to said resilient support.

20. The combination of claim 19 wherein said abutment means comprises a shoulder in contact with the outer periphery of said resilient support.

21. The combination of claim 18 wherein said resilient support comprises alternate layers of resilient material and stiffener material.

22. The combination of claim 21 wherein said restraining means comprises alternating layers of said resilient material, spirally wound flat members and said stiffener material.

23. The combination of claim 21 wherein said restraining means comprises alternating layers of said resilient material, stacked flat members and said stiffener material.

24. The combination of claim 22 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 plurality of apertures extending from the lower surface thereof upwardly into the lower most layer of stiffener material, and wherein said abutment means includes a first plurality of dowel members extending downwardly from said first coupling means with each of said dowel members received 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 plurality of dowel members received In a corresponding one of said second plurality of apertures.

25. The combination of claim 10 whereon said energy absorber means comprises a lead core.