Note: Descriptions are shown in the official language in which they were submitted.
~ L2'~
~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
"
, . ... . .
3 ~ 3~
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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4 1~
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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- 5
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.
. ..
7 3I~ P~
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~
9 ~2~
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
,
. .
, . . ................................. . .
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.
:
- 12 ~ % ~ 3~
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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13 '~L~ 3~
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
14 ~ 2qL~
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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