Research ArticleLateral Response Comparison of Unbonded ElastomericBearings Reinforced with Carbon Fiber Mesh and Steel

Ali Karimzadeh Naghshineh Ugurhan Akyuz and Alp Caner

Department of Civil Engineering Middle East Technical University Universiteler MahallesiDumlupinar Bulvari No 1 Cankaya 06800 Ankara Turkey

Correspondence should be addressed to Ali Karimzadeh Naghshineh ali naghshineyahoocom

Received 12 November 2014 Revised 10 December 2014 Accepted 25 December 2014

Academic Editor Mohammad Elahinia

Copyright copy 2015 Ali Karimzadeh Naghshineh et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

The vertical and horizontal stiffness used in design of bearings have been established in the last few decades At the meantimeapplicability of the theoretical approach developed to estimate vertical stiffness of the fiber-reinforced bearings has been verified indifferent academic studies The suitability of conventional horizontal stiffness equation developed for elastomeric material mainlyfor steel-reinforced elastomeric bearings has not been tested in detail for use of fiber-reinforced elastomeric bearings In thisresearch lateral response of fiber mesh-reinforced elastomeric bearings has been determined through experimental tests and theresults have been compared by corresponding values pertaining to the steel-reinforced bearings Within the test program eightpairs of fiber mesh-reinforced bearings and eight pairs of steel-reinforced bearings are subjected to different levels of compressivestress and cyclic shear strains Fiber-reinforced elastomeric bearings may be more favorable to be used in seismic regions due tolower horizontal stiffness that can result in mitigation of seismic forces for levels of 100 shear strain Damping properties ofthese types of fiber mesh-reinforced bearings dependmostly on the selection of elastomeric material compounds Suggestions havebeen made for the lateral response of fiber-reinforced elastomeric bearings It has also been determined that the classical equationfor lateral stiffness based on linear elastic behavior assumptions developed for elastomeric bearings does not always apply to thefiber-reinforced ones

1 Introduction

Fiber mesh-reinforced elastomeric bearings are becomingpopular in the academic researches Most of the design equa-tions used for fiber mesh-reinforced bearings are adaptedfrom the known elastomeric material behavior or mainly theones developed for the steel-reinforced elastomeric bearingsLack of a complete lateral response comparison betweenfull size fiber-reinforced and steel-reinforced bearings andlimited amount of research on lateral structural response offiber-reinforced bearings in the known literature are themainreasons to conduct this research

Elastomeric bearings reinforced by steel plates are themost common types of the bearings used for seismic isolationor standard bearings of the structures In an attempt todecrease the weight and cost of these bearings Kelly [1] intro-duced a certain type of fiber-reinforced elastomeric bearings

and showed that these bearings can provide adequate verticalstiffness for base isolation

Fiber-reinforced elastomeric bearings were studied bymany researchers during the past decades Moon et al [2]manufactured fiber-reinforced elastomeric bearings usingdifferent types of fiber reinforcement They compared theperformance of these bearings and concluded that carbonfiber-reinforced bearings have superior performance param-eters Ashkezari et al [3] manufactured some specimensof multilayer elastomeric seismic isolators reinforced bylayers of woven carbon and steel They concluded that ldquosteellike fiber-reinforced elastomeric isolatorsrdquo (SLFREI) can beused in seismic isolation of structures Compared to othersToopchi-Nezhad et al [4 5] studied the lateral response offiber-reinforced bearings using shake table testing methodZhang et al [6] studied the mechanical properties of FRP-based elastomeric isolators after manufacturing and testing

Hindawi Publishing CorporationShock and VibrationVolume 2015 Article ID 208045 10 pageshttpdxdoiorg1011552015208045

2 Shock and Vibration

Table 1 Properties of steel-reinforced and fiber-reinforced bearings

Type 119886

(mm)119887

(mm)119877

(mm)119905119888

(mm)119905119903

(mm)119905119904 or119891(mm) 119899

119903119899119904

119879119903

(mm) 119867

Shapefactor

1198781119910 250 400 lowast 5 8 20 7 6 50 6200 9281198651119910 250 400 lowast 5 8 0125 7 6 50 5075 9281198781119911 250 400 lowast lowast 5 20 7 6 35 4700 14851198651119911 250 400 lowast lowast 5 0125 7 6 35 3575 14851198782119910 300 300 lowast 5 6 20 7 6 40 5200 12081198652119910 300 300 lowast 5 6 0125 7 6 40 4075 12081198782119911 300 300 lowast lowast 5 20 7 6 35 4700 14501198652119911 300 300 lowast lowast 5 0125 7 6 35 3575 14501198783119910 lowast lowast 100 lowast 10 20 4 3 40 4600 4751198653119910 lowast lowast 100 lowast 10 0125 4 3 40 4038 4751198783119911 lowast lowast 100 lowast 5 20 10 9 50 6800 9501198653119911 lowast lowast 100 lowast 5 0125 10 9 50 5113 9501198784119910 150 150 lowast lowast 4 10 12 11 48 5900 8751198654119910 150 150 lowast lowast 4 0125 12 11 48 4938 8751198784119911 150 150 lowast lowast 2 10 20 19 40 5900 17501198654119911 150 150 lowast lowast 2 0125 20 19 40 4238 1750lowastNot applicable

a number of samples Calabrese and Kelly [7] reviewedthe response of fiber-reinforced bearings and compared theresults of finite element analysis with the proposed theoreticalapproach Russo et al [8] studied the shear behavior of fiber-reinforced elastomeric bearings and they proposed a newexpression for the horizontal stiffness of the fiber-reinforcedbearings They studied the deformed configuration of fiber-reinforced bearings under shear strains Hedayati Dezfuliand Alam [9] probed the effect of physical and mechanicalproperties such as thickness and shear modulus of rubberlayers on the performance of the FREIs in bonded appli-cations Karimzadeh Naghshineh et al [10] compared thefundamental properties of fiber mesh-reinforced isolatorswith the conventional steel-reinforced isolators Toopchi-Nezhad [11] presented two simplified analytical models forhorizontal stiffness evaluation of unbonded fiber-reinforcedelastomeric bearings

Carbon fibermeshwith opening described in the study byKarimzadeh Naghshineh et al [10] was used in this researchand details of the reinforcing materials can be found in thestudy by Karimzadeh Naghshineh et al [10] Effects of fiberflexibility on vertical stiffness of the bearings have been stud-ied by Kelly and Takhirov [12] In previous researches thereis not any experimental study which compares the lateralstiffness of unbonded fiber- and steel-reinforced bearings Inthis research lateral response of fiber- and steel-reinforcedbearings in unbonded application will be compared throughinvestigating results of experimental program To investigatethe effect of parameters such as geometry and size onlateral response of fibe-reinforced bearings eight pairs offiber-reinforced bearings with different properties are man-ufactured Steel-reinforced bearings are manufactured with

the same geometric and elastomeric properties used for fiber-reinforced bearings Under these conditions a comprehen-sive comparison between fiber- and steel-reinforced bearingshas been made For verification purposes suggestions for thelateral response of fiber-reinforced bearings have been made

It shall be noted that fiber mesh-reinforced elastomericbearings are typically manufactured using ldquocoldrdquo manu-facturing technique that involves applying bonding agentsbetween layers of fiber mesh and rubber To eliminate use ofbonding agent between elastomericmaterials and reinforcingmaterial vulcanization through high temperatures is selectedas the manufacturing process that has also been used in thetypical manufacturing method for steel-reinforced bearingsThis type of manufacturing process was also used by Russoand Pauletta [13]

2 Materials and Methods

21 Test Specimens Several samples of fiber- and steel-reinforced bearings were manufactured In manufacturingall of these bearings high damping natural rubber with thenominal stiffness of 60 Shore 119860 was used The nominal shearmodulus of rubber material was 07MPa plusmn 015MPa and theeffective damping of rubber compound was around 8 Geo-metrical properties of all bearings were presented in Table 1In Table 1 the type is denoted by three characters inwhich thefirst character displays the reinforcement type (119865 for fiber and119878 for steel) the second character shows the specimen number(1 2 3 or 4) and the third character indicates the shape factorof specimen (119911 represents a higher shape factor comparedto 119910) In the second and third columns 119886 is used for width

Shock and Vibration 3

H

Reinforcement (ts or f)

Top elastomer layer (tc)

Middle elastomer layer (tr)

Bottom elastomer layer (tc)

Figure 1 Schematic view of bearing parameters

of the bearing and 119887 is used for the length of the bearingIn the fourth column 119877 shows radius of circular bearingsin the fifth column 119905

119888is the thickness of top and bottom

cover layers In the sixth column 119905119903is the thickness of middle

elastomer layers In the seventh column 119905119904 or119891 is the thickness

of reinforcing steel plates or fiber reinforcement In the eighthcolumn 119899

119903is number of elastomer layers with considering

the top and bottom cover layers In the ninth column 119899119904

is the number of reinforcing layers In the tenth column119879119903is the total thickness of elastomer layers In the eleventh

column119867 is the total thickness of bearing with consideringthe reinforcement thickness Shape factor of bearing is usuallydefined as the ratio of loaded area to force-free area Figure 1illustrates the bearings parameters in schematic manner

22 Horizontal Shear Stiffness Test Setup Seismic isolatortesting system available in Structure Engineering Laboratoryof Middle East Technical University has been designed to testthe isolators in horizontal direction under constant verticalloadThis system is capable of conducting in-plane horizontalcyclic loading tests as shown in Figures 2(a) and 2(b) Thismachine can test a pair of elastomeric bearings by applyingvertical pressure and keeping it constant at a desired leveland then implementing cyclic displacement control loadingin horizontal direction Load capacity of testing system isabout 3000 kN in vertical direction and this value reduces to600 kN for horizontal direction

Test setup is composed of two distinct main loadingsystems in horizontal and vertical directions loading systemin vertical direction is used for applying the desired levelof pressure and loading system in horizontal direction iscapable of controlling the applied displacement Loadingsystem in vertical direction with its adjustable upper plateprovides testing opportunity for different type and size ofbearings Horizontal loading system is capable of sliding onrails located on vertical support plates to adjust the insertedhorizontal load in accordance with the bearingrsquos heightAlso horizontal loading system can be relocated on bottomsupport plates to increase the horizontal loading capacityTwo linear variable differential transformers (LVDT) placedon middle sliding plate were used to measure the horizontal

displacement of the bearing during shear test Data acqui-sition system was run by a PC Windows-based control andacquisition program called StrainSmart 6000 developed byVishay Precision GroupWendell USA System 6000 featuresdata acquisition rates of up to 10000 samples per second perchannel It is worth noting that the average sampling rate was100 per second in all of the tests

23 Test Procedure Bearings were tested under horizontaldisplacement control during the horizontal test Bearingswere subjected to shear in pairs under a vertical loadequivalent to a pressure of 690 and 345MPa The selectedcompressive pressures are typical design pressures for thistype of bearings They were tested in cyclic shear with threefully reversed cycles at three maximum strain levels of 2550 and 100 based on the total rubber thickness Hori-zontal stiffness of the bearings and their equivalent viscousdamping ratio were calculated by analyzing the hysteresisloops obtained during this test

The loading history of the horizontal test for bearingsis presented in Figure 3 and this figure depicts the inputsignal for specimens Different seismic isolation systems havealso been tested at the Middle East Technical University byPinarbasi et al [14] Ozkaya et al [15] and Caner et al [16]

Loading history of bearings affects the response of thebearings in such a way that during the first several cycles thebearing has higher effective horizontal stiffness and damping(scragging effect) By the third cycle the response of thebearing has stabilized and the responses presented in thisstudy are stabilized response of bearing

24 Investigated Test Parameters for Elastomeric BearingsResults of horizontal shear test were used to calculate thehorizontal stiffness of the bearings A simple calculationof shear stiffness based on the values of peak force anddisplacement is defined as

119870ℎ

eff =

1003816100381610038161003816119865+1003816100381610038161003816+1003816100381610038161003816119865minus1003816100381610038161003816

|119889+| + |119889minus|

(1)

where 119889+ and 119889minus are the maximum positive and maximumnegative test displacements respectively and 119865+ and 119865minus arethe forces at instance of displacements 119889+ and 119889minus respectively[17] This stiffness is interpreted as the effective or overallstiffness of the bearing during the test This stiffness is usedto calculate the stored or elastic energy of the bearings duringcyclic tests

The hysteresis loops were also analyzed to obtain theequivalent viscous damping ratio of the bearing for eachtest A hysteresis loop represents the plot of force againstdisplacement and therefore the area contained within sucha loop represents the energy dissipated by the bearing

The equivalent viscous damping ratio exhibited by thebearing is evaluated in the usual structural engineeringfashion [18]

120585 =

119882119889

4120587119882119904

(2)

4 Shock and Vibration

(a) Testing system

(A) Push-pull steel plate(B) Bearings to be tested (two bearings are tested)(C) Hydraulic cylinder (for application of vertical loads)(D) Hydraulic cylinder (for application of horizontal loads)

(E) Load cell in the vertical direction(F) Load cell in the horizontal direction (G) LVDT

204

260

C

GAB

B

E

D D

2215

3847

1515

1533

70

F

4

128

178

(b) Schematic layout (dimensions cm)

Figure 2 General view of the horizontal shear test equipment

0 6 12 18 24 30 36 42

Hor

izon

tal s

trai

n (

)

Time (s)

Horizontal test signal for bearing

minus100

minus75

minus50

minus25

0

25

50

75

100

Figure 3 Input signal for horizontal shear test with 345MPa and690MPa vertical preload

where119882119889represents a dissipated energy equal to the hystere-

sis loop area and119882119904corresponds to stored or elastic energy

defined by the following formula

119882119904= 119870ℎ

eff119889max2

2

(3)

Here 119889max is the average of positive and negative maximumdisplacements and is defined as

119889max =

1003816100381610038161003816119889+1003816100381610038161003816+1003816100381610038161003816119889minus1003816100381610038161003816

2

(4)

Shock and Vibration 5

Table 2 Equivalent viscous damping values

Type and damp ratio

Equivalent viscous damping 120585 under vertical pressure (MPa)345 690

Strain level () Strain level ()25 50 100 Average 25 50 100 Average

1198781119910 116 108 136 12 86 10 96 941198651119910 107 107 109 108 75 82 98 85120585119904120585119891

109 101 125 111 115 123 098 1111198781119911 102 132 125 1197 67 92 109 8931198651119911 134 166 150 150 74 121 132 109120585119904120585119891

076 079 083 080 091 076 083 0821198782119910 84 116 132 1107 58 88 87 771198652119910 117 101 87 102 65 109 79 84120585119904120585119891

072 115 151 109 090 081 109 0921198782119911 74 113 143 110 53 78 124 851198652119911 94 104 89 96 6 91 76 76120585119904120585119891

079 109 159 115 088 086 162 1121198783119910 58 85 102 82 52 63 78 641198653119910 69 85 92 82 5 58 72 60120585119904120585119891

084 100 111 100 104 109 109 1071198783119911 85 69 77 77 51 5 63 551198653119911 6 78 8 73 57 55 75 62120585119904120585119891

142 089 097 106 088 090 084 0881198784119910 101 114 105 107 99 88 99 951198654119910 98 93 84 92 98 86 8 88120585119904120585119891

103 123 126 116 101 102 123 1081198784119911 97 103 88 96 97 81 95 911198654119911 108 101 97 102 10 87 84 90120585119904120585119891

090 102 091 094 098 093 114 101

The linear viscous model assumes that the energy dissipatedin each cycle is linear with the frequency and quadratic withthe displacement [18]

Dynamic response of an isolated structure dependsmainly on the horizontal stiffness of isolators The followingequation for horizontal stiffness 119870

ℎ is based on the simple

analysis that can be found in strength of material text booksand is used for both steel and fiber reinforcement conditionsalthough the equation is developed for elastomeric materials

119870ℎ=

119860119866

119879119903

(5)

where 119870ℎis horizontal stiffness of bearing (kNm) 119866 is

shear modulus of elastomer (MPa) 119879119903is total thickness of

elastomeric material (mm) and 119860 is plan area of the bearing(mm2)

3 Test Results and Discussion

Results of horizontal shear test are presented in this part InTable 2 a comparison of numerical values of the damping of

both types of bearings at different strain levels is presentedThe average damping of the bearing is the arithmetic meanof the damping values during all the cycles As it is clearfrom the presented results in Table 2 there is not thatmuch of difference between the average values of dampingpertaining to the fiber mesh- and steel-reinforced bearingsThemaximumdifference between the average damping ratiosis about 20 The main source of energy dissipation inthese elastomeric bearings is rubber compound and selectionof reinforcement material is believed not to result in bigdifference in damping valuesThedamping values in this kindof fiber- and steel-reinforced bearing are within reasonabletolerances

Horizontal effective stiffness test results of the bearingsare presented in Table 3 The horizontal stiffness of thesteel-reinforced bearings and that of fiber mesh-reinforcedbearings do not differ much for large size bearings whichhad higher stiffness compared to the small sizes as expectedLarger specimens are more stable to rollover due to theirgeometrical properties and high ratios of area to elastomerthickness and rollover starts at high levels of shear strain inthese bearings

6 Shock and Vibration

The same observation cannot be made for the small sizebearings due to the early rollover response of the fiber mesh-reinforced bearings that decreased the stiffness at larger strainvalues significantly as shown in Figures 4(a)ndash4(d) In all ofthe shear tests as strain level increases effective stiffness ofbearings decreases Increase in vertical preload resulted inhigher values of horizontal stiffness

For Type 1 bearings large size ones at lower strainlevels (up to 50) stiffness of fiber-reinforced bearings wasslightly greater than the steel-reinforced ones As strain levelincreases rollover of fiber-reinforced bearings commencedand this phenomenon led to a decrease in stiffness In Type 2bearings stiffness of fiber-reinforced bearings at lower strainlevels is greater than steel-reinforced ones but as rolloverstarts their stiffness decreases drastically For Types 3 and4 bearings decrease in stiffness developed at lower strainlevels This observation could be attributed to the small sizeof the bearings because rollover deformation is affected by theratio between the bearing thickness and base side length andbearings with smaller ratios have more potential to developrollover response than larger specimens In larger specimensrollover starts at larger levels of strain compared to small sizebearings In steel-reinforced bearings the same observationof rollover happens at larger strain levels compared to fiber-reinforced bearings The governing trend in the tested speci-mens is that as strain level increases the difference betweenthe effective stiffness of the steel-reinforced bearings andthat of fiber-reinforced bearings increases and the amountof increase depends on several parameters such as size andvertical pressure

The minimum divergence in stiffness of 1 is observedat high compressive stress levels for the bearings with largerplan area and thicker total elastomeric layers The maximumdivergence in stiffness of 78 is observed at low compressivestress levels for the small size bearing with lower totalthickness of elastomeric materials

The conventional horizontal stiffness presented in (5)has two components one being material property and theother being size The material property is presented by shearmodulus 119866 and the size index is presented by 119860119879

119903ratio

In all the tests the shear modulus 119866 is the same Thereforea relationship for size effect versus correction factor isdeveloped within this research The nonlinear relationshipbetween horizontal stiffness of steel-reinforced bearings andthat of fiber mesh-reinforced bearings can be represented by

119870(eff)119904

119870(eff)119891= 119891(

119860

119879119903

) = 120572 (6)

where119870(eff)119904 is horizontal effective stiffness of steel-reinforced

bearings119870(eff)119891 is horizontal effective stiffness of fiber mesh-

reinforced bearings and 120572 is nonlinear correction factor forsize effect

It has been experimentally determined that the 120572 factorcan be obtained from best fit curve using Figure 5

120572 = 609 (

119860

119879119903

)

minus023

(7)

Therefore the effective horizontal stiffness of fiber mesh-reinforced bearings can be recommended for 100 strain

119870(eff)119891 =

119866

609

(

119860

119879119903

)

123

119860

119879119903

le 3000 (8)

No correction is suggested for 119860119879119903

values exceeding3000mm2mm and the effective stiffness for elastomericmaterial in (5) can be applied to fiber mesh-reinforcedbearings For strain levels less than 100 linear interpolationfor the values given in Table 3 can be recommended to use

The proposed equation does not take account of theparticular rollover deformation of fiber-reinforced bearingsbut as in the studies by Kelly [19 20] for example theexpression for estimating the rollout stability limit changesby only 5 percent when the compression load is doubled Sothis equation can be used to determine the horizontal stiffnessof the fiber-reinforced bearings in the range of discussedpressures (345ndash690MPa)

Unbonded small size fiber-reinforced bearings candevelop very low horizontal stiffness compared to steel-reinforced bearings and this may be considered as anadvantage in design as long as rollover deformations of thebearings are stable It shall be noted that the rollover didnot develop any instability during tests The reason is thatall the specimens had curves with increasing resisting forceat an increase of the applied shear deformation No zero ornegative tangent stiffness was observed in test results andafter unloading there was not any residual deformation inthe bearings All the bearings sustained the applied loadand strain levels and no visible damage was developed inbearings as shown in Figure 6

It can be concluded that effective lateral stiffness of fiber-reinforced bearings is affected by several parameters suchas geometrical properties strain level and vertical preloadIt can be stated that rollover response of fiber-reinforcedbearing is beneficial if the bearing remains stable horizontally

Hysteresis loops obtained in horizontal shear test forselected bearings are plotted in terms of horizontal displace-ment versus horizontal load as shown in Figures 7(a)ndash7(d)In this figure horizontal axis corresponds to displacementof bearings (mm) and vertical axis corresponds to horizontalforce (kN) Horizontal stiffness for a single bearing is consid-ered to be the half of the values since the tests are conductedsimultaneously on two bearings

4 Conclusion

Test results of new types of fiber mesh-reinforced elastomericbearings and conventional isolators are comparedThe obser-vations made during the tests can be summarized as follows

(i) The conventional horizontal stiffness used in designof elastomeric materials does not always apply to thefibermesh-reinforced bearings At high levels of shearstrain there is a significant deviation in horizontalstiffness of small size fiber mesh-reinforced bearingscompared to steel-reinforced bearings A nonlinear

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

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2 Shock and Vibration

Table 1 Properties of steel-reinforced and fiber-reinforced bearings

Type 119886

(mm)119887

(mm)119877

(mm)119905119888

(mm)119905119903

(mm)119905119904 or119891(mm) 119899

119903119899119904

119879119903

(mm) 119867

Shapefactor

1198781119910 250 400 lowast 5 8 20 7 6 50 6200 9281198651119910 250 400 lowast 5 8 0125 7 6 50 5075 9281198781119911 250 400 lowast lowast 5 20 7 6 35 4700 14851198651119911 250 400 lowast lowast 5 0125 7 6 35 3575 14851198782119910 300 300 lowast 5 6 20 7 6 40 5200 12081198652119910 300 300 lowast 5 6 0125 7 6 40 4075 12081198782119911 300 300 lowast lowast 5 20 7 6 35 4700 14501198652119911 300 300 lowast lowast 5 0125 7 6 35 3575 14501198783119910 lowast lowast 100 lowast 10 20 4 3 40 4600 4751198653119910 lowast lowast 100 lowast 10 0125 4 3 40 4038 4751198783119911 lowast lowast 100 lowast 5 20 10 9 50 6800 9501198653119911 lowast lowast 100 lowast 5 0125 10 9 50 5113 9501198784119910 150 150 lowast lowast 4 10 12 11 48 5900 8751198654119910 150 150 lowast lowast 4 0125 12 11 48 4938 8751198784119911 150 150 lowast lowast 2 10 20 19 40 5900 17501198654119911 150 150 lowast lowast 2 0125 20 19 40 4238 1750lowastNot applicable

a number of samples Calabrese and Kelly [7] reviewedthe response of fiber-reinforced bearings and compared theresults of finite element analysis with the proposed theoreticalapproach Russo et al [8] studied the shear behavior of fiber-reinforced elastomeric bearings and they proposed a newexpression for the horizontal stiffness of the fiber-reinforcedbearings They studied the deformed configuration of fiber-reinforced bearings under shear strains Hedayati Dezfuliand Alam [9] probed the effect of physical and mechanicalproperties such as thickness and shear modulus of rubberlayers on the performance of the FREIs in bonded appli-cations Karimzadeh Naghshineh et al [10] compared thefundamental properties of fiber mesh-reinforced isolatorswith the conventional steel-reinforced isolators Toopchi-Nezhad [11] presented two simplified analytical models forhorizontal stiffness evaluation of unbonded fiber-reinforcedelastomeric bearings

Carbon fibermeshwith opening described in the study byKarimzadeh Naghshineh et al [10] was used in this researchand details of the reinforcing materials can be found in thestudy by Karimzadeh Naghshineh et al [10] Effects of fiberflexibility on vertical stiffness of the bearings have been stud-ied by Kelly and Takhirov [12] In previous researches thereis not any experimental study which compares the lateralstiffness of unbonded fiber- and steel-reinforced bearings Inthis research lateral response of fiber- and steel-reinforcedbearings in unbonded application will be compared throughinvestigating results of experimental program To investigatethe effect of parameters such as geometry and size onlateral response of fibe-reinforced bearings eight pairs offiber-reinforced bearings with different properties are man-ufactured Steel-reinforced bearings are manufactured with

the same geometric and elastomeric properties used for fiber-reinforced bearings Under these conditions a comprehen-sive comparison between fiber- and steel-reinforced bearingshas been made For verification purposes suggestions for thelateral response of fiber-reinforced bearings have been made

It shall be noted that fiber mesh-reinforced elastomericbearings are typically manufactured using ldquocoldrdquo manu-facturing technique that involves applying bonding agentsbetween layers of fiber mesh and rubber To eliminate use ofbonding agent between elastomericmaterials and reinforcingmaterial vulcanization through high temperatures is selectedas the manufacturing process that has also been used in thetypical manufacturing method for steel-reinforced bearingsThis type of manufacturing process was also used by Russoand Pauletta [13]

2 Materials and Methods

21 Test Specimens Several samples of fiber- and steel-reinforced bearings were manufactured In manufacturingall of these bearings high damping natural rubber with thenominal stiffness of 60 Shore 119860 was used The nominal shearmodulus of rubber material was 07MPa plusmn 015MPa and theeffective damping of rubber compound was around 8 Geo-metrical properties of all bearings were presented in Table 1In Table 1 the type is denoted by three characters inwhich thefirst character displays the reinforcement type (119865 for fiber and119878 for steel) the second character shows the specimen number(1 2 3 or 4) and the third character indicates the shape factorof specimen (119911 represents a higher shape factor comparedto 119910) In the second and third columns 119886 is used for width

Shock and Vibration 3

H

Reinforcement (ts or f)

Top elastomer layer (tc)

Middle elastomer layer (tr)

Bottom elastomer layer (tc)

Figure 1 Schematic view of bearing parameters

of the bearing and 119887 is used for the length of the bearingIn the fourth column 119877 shows radius of circular bearingsin the fifth column 119905

119888is the thickness of top and bottom

cover layers In the sixth column 119905119903is the thickness of middle

elastomer layers In the seventh column 119905119904 or119891 is the thickness

of reinforcing steel plates or fiber reinforcement In the eighthcolumn 119899

119903is number of elastomer layers with considering

the top and bottom cover layers In the ninth column 119899119904

is the number of reinforcing layers In the tenth column119879119903is the total thickness of elastomer layers In the eleventh

column119867 is the total thickness of bearing with consideringthe reinforcement thickness Shape factor of bearing is usuallydefined as the ratio of loaded area to force-free area Figure 1illustrates the bearings parameters in schematic manner

22 Horizontal Shear Stiffness Test Setup Seismic isolatortesting system available in Structure Engineering Laboratoryof Middle East Technical University has been designed to testthe isolators in horizontal direction under constant verticalloadThis system is capable of conducting in-plane horizontalcyclic loading tests as shown in Figures 2(a) and 2(b) Thismachine can test a pair of elastomeric bearings by applyingvertical pressure and keeping it constant at a desired leveland then implementing cyclic displacement control loadingin horizontal direction Load capacity of testing system isabout 3000 kN in vertical direction and this value reduces to600 kN for horizontal direction

Test setup is composed of two distinct main loadingsystems in horizontal and vertical directions loading systemin vertical direction is used for applying the desired levelof pressure and loading system in horizontal direction iscapable of controlling the applied displacement Loadingsystem in vertical direction with its adjustable upper plateprovides testing opportunity for different type and size ofbearings Horizontal loading system is capable of sliding onrails located on vertical support plates to adjust the insertedhorizontal load in accordance with the bearingrsquos heightAlso horizontal loading system can be relocated on bottomsupport plates to increase the horizontal loading capacityTwo linear variable differential transformers (LVDT) placedon middle sliding plate were used to measure the horizontal

displacement of the bearing during shear test Data acqui-sition system was run by a PC Windows-based control andacquisition program called StrainSmart 6000 developed byVishay Precision GroupWendell USA System 6000 featuresdata acquisition rates of up to 10000 samples per second perchannel It is worth noting that the average sampling rate was100 per second in all of the tests

23 Test Procedure Bearings were tested under horizontaldisplacement control during the horizontal test Bearingswere subjected to shear in pairs under a vertical loadequivalent to a pressure of 690 and 345MPa The selectedcompressive pressures are typical design pressures for thistype of bearings They were tested in cyclic shear with threefully reversed cycles at three maximum strain levels of 2550 and 100 based on the total rubber thickness Hori-zontal stiffness of the bearings and their equivalent viscousdamping ratio were calculated by analyzing the hysteresisloops obtained during this test

The loading history of the horizontal test for bearingsis presented in Figure 3 and this figure depicts the inputsignal for specimens Different seismic isolation systems havealso been tested at the Middle East Technical University byPinarbasi et al [14] Ozkaya et al [15] and Caner et al [16]

Loading history of bearings affects the response of thebearings in such a way that during the first several cycles thebearing has higher effective horizontal stiffness and damping(scragging effect) By the third cycle the response of thebearing has stabilized and the responses presented in thisstudy are stabilized response of bearing

24 Investigated Test Parameters for Elastomeric BearingsResults of horizontal shear test were used to calculate thehorizontal stiffness of the bearings A simple calculationof shear stiffness based on the values of peak force anddisplacement is defined as

119870ℎ

eff =

1003816100381610038161003816119865+1003816100381610038161003816+1003816100381610038161003816119865minus1003816100381610038161003816

|119889+| + |119889minus|

(1)

where 119889+ and 119889minus are the maximum positive and maximumnegative test displacements respectively and 119865+ and 119865minus arethe forces at instance of displacements 119889+ and 119889minus respectively[17] This stiffness is interpreted as the effective or overallstiffness of the bearing during the test This stiffness is usedto calculate the stored or elastic energy of the bearings duringcyclic tests

The hysteresis loops were also analyzed to obtain theequivalent viscous damping ratio of the bearing for eachtest A hysteresis loop represents the plot of force againstdisplacement and therefore the area contained within sucha loop represents the energy dissipated by the bearing

The equivalent viscous damping ratio exhibited by thebearing is evaluated in the usual structural engineeringfashion [18]

120585 =

119882119889

4120587119882119904

(2)

4 Shock and Vibration

(a) Testing system

(A) Push-pull steel plate(B) Bearings to be tested (two bearings are tested)(C) Hydraulic cylinder (for application of vertical loads)(D) Hydraulic cylinder (for application of horizontal loads)

(E) Load cell in the vertical direction(F) Load cell in the horizontal direction (G) LVDT

204

260

C

GAB

B

E

D D

2215

3847

1515

1533

70

F

4

128

178

(b) Schematic layout (dimensions cm)

Figure 2 General view of the horizontal shear test equipment

0 6 12 18 24 30 36 42

Hor

izon

tal s

trai

n (

)

Time (s)

Horizontal test signal for bearing

minus100

minus75

minus50

minus25

0

25

50

75

100

Figure 3 Input signal for horizontal shear test with 345MPa and690MPa vertical preload

where119882119889represents a dissipated energy equal to the hystere-

sis loop area and119882119904corresponds to stored or elastic energy

defined by the following formula

119882119904= 119870ℎ

eff119889max2

2

(3)

Here 119889max is the average of positive and negative maximumdisplacements and is defined as

119889max =

1003816100381610038161003816119889+1003816100381610038161003816+1003816100381610038161003816119889minus1003816100381610038161003816

2

(4)

Shock and Vibration 5

Table 2 Equivalent viscous damping values

Type and damp ratio

Equivalent viscous damping 120585 under vertical pressure (MPa)345 690

Strain level () Strain level ()25 50 100 Average 25 50 100 Average

1198781119910 116 108 136 12 86 10 96 941198651119910 107 107 109 108 75 82 98 85120585119904120585119891

109 101 125 111 115 123 098 1111198781119911 102 132 125 1197 67 92 109 8931198651119911 134 166 150 150 74 121 132 109120585119904120585119891

076 079 083 080 091 076 083 0821198782119910 84 116 132 1107 58 88 87 771198652119910 117 101 87 102 65 109 79 84120585119904120585119891

072 115 151 109 090 081 109 0921198782119911 74 113 143 110 53 78 124 851198652119911 94 104 89 96 6 91 76 76120585119904120585119891

079 109 159 115 088 086 162 1121198783119910 58 85 102 82 52 63 78 641198653119910 69 85 92 82 5 58 72 60120585119904120585119891

084 100 111 100 104 109 109 1071198783119911 85 69 77 77 51 5 63 551198653119911 6 78 8 73 57 55 75 62120585119904120585119891

142 089 097 106 088 090 084 0881198784119910 101 114 105 107 99 88 99 951198654119910 98 93 84 92 98 86 8 88120585119904120585119891

103 123 126 116 101 102 123 1081198784119911 97 103 88 96 97 81 95 911198654119911 108 101 97 102 10 87 84 90120585119904120585119891

090 102 091 094 098 093 114 101

The linear viscous model assumes that the energy dissipatedin each cycle is linear with the frequency and quadratic withthe displacement [18]

Dynamic response of an isolated structure dependsmainly on the horizontal stiffness of isolators The followingequation for horizontal stiffness 119870

ℎ is based on the simple

analysis that can be found in strength of material text booksand is used for both steel and fiber reinforcement conditionsalthough the equation is developed for elastomeric materials

119870ℎ=

119860119866

119879119903

(5)

where 119870ℎis horizontal stiffness of bearing (kNm) 119866 is

shear modulus of elastomer (MPa) 119879119903is total thickness of

elastomeric material (mm) and 119860 is plan area of the bearing(mm2)

3 Test Results and Discussion

Results of horizontal shear test are presented in this part InTable 2 a comparison of numerical values of the damping of

both types of bearings at different strain levels is presentedThe average damping of the bearing is the arithmetic meanof the damping values during all the cycles As it is clearfrom the presented results in Table 2 there is not thatmuch of difference between the average values of dampingpertaining to the fiber mesh- and steel-reinforced bearingsThemaximumdifference between the average damping ratiosis about 20 The main source of energy dissipation inthese elastomeric bearings is rubber compound and selectionof reinforcement material is believed not to result in bigdifference in damping valuesThedamping values in this kindof fiber- and steel-reinforced bearing are within reasonabletolerances

Horizontal effective stiffness test results of the bearingsare presented in Table 3 The horizontal stiffness of thesteel-reinforced bearings and that of fiber mesh-reinforcedbearings do not differ much for large size bearings whichhad higher stiffness compared to the small sizes as expectedLarger specimens are more stable to rollover due to theirgeometrical properties and high ratios of area to elastomerthickness and rollover starts at high levels of shear strain inthese bearings

6 Shock and Vibration

The same observation cannot be made for the small sizebearings due to the early rollover response of the fiber mesh-reinforced bearings that decreased the stiffness at larger strainvalues significantly as shown in Figures 4(a)ndash4(d) In all ofthe shear tests as strain level increases effective stiffness ofbearings decreases Increase in vertical preload resulted inhigher values of horizontal stiffness

For Type 1 bearings large size ones at lower strainlevels (up to 50) stiffness of fiber-reinforced bearings wasslightly greater than the steel-reinforced ones As strain levelincreases rollover of fiber-reinforced bearings commencedand this phenomenon led to a decrease in stiffness In Type 2bearings stiffness of fiber-reinforced bearings at lower strainlevels is greater than steel-reinforced ones but as rolloverstarts their stiffness decreases drastically For Types 3 and4 bearings decrease in stiffness developed at lower strainlevels This observation could be attributed to the small sizeof the bearings because rollover deformation is affected by theratio between the bearing thickness and base side length andbearings with smaller ratios have more potential to developrollover response than larger specimens In larger specimensrollover starts at larger levels of strain compared to small sizebearings In steel-reinforced bearings the same observationof rollover happens at larger strain levels compared to fiber-reinforced bearings The governing trend in the tested speci-mens is that as strain level increases the difference betweenthe effective stiffness of the steel-reinforced bearings andthat of fiber-reinforced bearings increases and the amountof increase depends on several parameters such as size andvertical pressure

The minimum divergence in stiffness of 1 is observedat high compressive stress levels for the bearings with largerplan area and thicker total elastomeric layers The maximumdivergence in stiffness of 78 is observed at low compressivestress levels for the small size bearing with lower totalthickness of elastomeric materials

The conventional horizontal stiffness presented in (5)has two components one being material property and theother being size The material property is presented by shearmodulus 119866 and the size index is presented by 119860119879

119903ratio

In all the tests the shear modulus 119866 is the same Thereforea relationship for size effect versus correction factor isdeveloped within this research The nonlinear relationshipbetween horizontal stiffness of steel-reinforced bearings andthat of fiber mesh-reinforced bearings can be represented by

119870(eff)119904

119870(eff)119891= 119891(

119860

119879119903

) = 120572 (6)

where119870(eff)119904 is horizontal effective stiffness of steel-reinforced

bearings119870(eff)119891 is horizontal effective stiffness of fiber mesh-

reinforced bearings and 120572 is nonlinear correction factor forsize effect

It has been experimentally determined that the 120572 factorcan be obtained from best fit curve using Figure 5

120572 = 609 (

119860

119879119903

)

minus023

(7)

Therefore the effective horizontal stiffness of fiber mesh-reinforced bearings can be recommended for 100 strain

119870(eff)119891 =

119866

609

(

119860

119879119903

)

123

119860

119879119903

le 3000 (8)

No correction is suggested for 119860119879119903

values exceeding3000mm2mm and the effective stiffness for elastomericmaterial in (5) can be applied to fiber mesh-reinforcedbearings For strain levels less than 100 linear interpolationfor the values given in Table 3 can be recommended to use

The proposed equation does not take account of theparticular rollover deformation of fiber-reinforced bearingsbut as in the studies by Kelly [19 20] for example theexpression for estimating the rollout stability limit changesby only 5 percent when the compression load is doubled Sothis equation can be used to determine the horizontal stiffnessof the fiber-reinforced bearings in the range of discussedpressures (345ndash690MPa)

Unbonded small size fiber-reinforced bearings candevelop very low horizontal stiffness compared to steel-reinforced bearings and this may be considered as anadvantage in design as long as rollover deformations of thebearings are stable It shall be noted that the rollover didnot develop any instability during tests The reason is thatall the specimens had curves with increasing resisting forceat an increase of the applied shear deformation No zero ornegative tangent stiffness was observed in test results andafter unloading there was not any residual deformation inthe bearings All the bearings sustained the applied loadand strain levels and no visible damage was developed inbearings as shown in Figure 6

It can be concluded that effective lateral stiffness of fiber-reinforced bearings is affected by several parameters suchas geometrical properties strain level and vertical preloadIt can be stated that rollover response of fiber-reinforcedbearing is beneficial if the bearing remains stable horizontally

Hysteresis loops obtained in horizontal shear test forselected bearings are plotted in terms of horizontal displace-ment versus horizontal load as shown in Figures 7(a)ndash7(d)In this figure horizontal axis corresponds to displacementof bearings (mm) and vertical axis corresponds to horizontalforce (kN) Horizontal stiffness for a single bearing is consid-ered to be the half of the values since the tests are conductedsimultaneously on two bearings

4 Conclusion

Test results of new types of fiber mesh-reinforced elastomericbearings and conventional isolators are comparedThe obser-vations made during the tests can be summarized as follows

(i) The conventional horizontal stiffness used in designof elastomeric materials does not always apply to thefibermesh-reinforced bearings At high levels of shearstrain there is a significant deviation in horizontalstiffness of small size fiber mesh-reinforced bearingscompared to steel-reinforced bearings A nonlinear

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Shock and Vibration 3

H

Reinforcement (ts or f)

Top elastomer layer (tc)

Middle elastomer layer (tr)

Bottom elastomer layer (tc)

Figure 1 Schematic view of bearing parameters

of the bearing and 119887 is used for the length of the bearingIn the fourth column 119877 shows radius of circular bearingsin the fifth column 119905

119888is the thickness of top and bottom

cover layers In the sixth column 119905119903is the thickness of middle

elastomer layers In the seventh column 119905119904 or119891 is the thickness

of reinforcing steel plates or fiber reinforcement In the eighthcolumn 119899

119903is number of elastomer layers with considering

the top and bottom cover layers In the ninth column 119899119904

is the number of reinforcing layers In the tenth column119879119903is the total thickness of elastomer layers In the eleventh

column119867 is the total thickness of bearing with consideringthe reinforcement thickness Shape factor of bearing is usuallydefined as the ratio of loaded area to force-free area Figure 1illustrates the bearings parameters in schematic manner

22 Horizontal Shear Stiffness Test Setup Seismic isolatortesting system available in Structure Engineering Laboratoryof Middle East Technical University has been designed to testthe isolators in horizontal direction under constant verticalloadThis system is capable of conducting in-plane horizontalcyclic loading tests as shown in Figures 2(a) and 2(b) Thismachine can test a pair of elastomeric bearings by applyingvertical pressure and keeping it constant at a desired leveland then implementing cyclic displacement control loadingin horizontal direction Load capacity of testing system isabout 3000 kN in vertical direction and this value reduces to600 kN for horizontal direction

Test setup is composed of two distinct main loadingsystems in horizontal and vertical directions loading systemin vertical direction is used for applying the desired levelof pressure and loading system in horizontal direction iscapable of controlling the applied displacement Loadingsystem in vertical direction with its adjustable upper plateprovides testing opportunity for different type and size ofbearings Horizontal loading system is capable of sliding onrails located on vertical support plates to adjust the insertedhorizontal load in accordance with the bearingrsquos heightAlso horizontal loading system can be relocated on bottomsupport plates to increase the horizontal loading capacityTwo linear variable differential transformers (LVDT) placedon middle sliding plate were used to measure the horizontal

displacement of the bearing during shear test Data acqui-sition system was run by a PC Windows-based control andacquisition program called StrainSmart 6000 developed byVishay Precision GroupWendell USA System 6000 featuresdata acquisition rates of up to 10000 samples per second perchannel It is worth noting that the average sampling rate was100 per second in all of the tests

23 Test Procedure Bearings were tested under horizontaldisplacement control during the horizontal test Bearingswere subjected to shear in pairs under a vertical loadequivalent to a pressure of 690 and 345MPa The selectedcompressive pressures are typical design pressures for thistype of bearings They were tested in cyclic shear with threefully reversed cycles at three maximum strain levels of 2550 and 100 based on the total rubber thickness Hori-zontal stiffness of the bearings and their equivalent viscousdamping ratio were calculated by analyzing the hysteresisloops obtained during this test

The loading history of the horizontal test for bearingsis presented in Figure 3 and this figure depicts the inputsignal for specimens Different seismic isolation systems havealso been tested at the Middle East Technical University byPinarbasi et al [14] Ozkaya et al [15] and Caner et al [16]

Loading history of bearings affects the response of thebearings in such a way that during the first several cycles thebearing has higher effective horizontal stiffness and damping(scragging effect) By the third cycle the response of thebearing has stabilized and the responses presented in thisstudy are stabilized response of bearing

24 Investigated Test Parameters for Elastomeric BearingsResults of horizontal shear test were used to calculate thehorizontal stiffness of the bearings A simple calculationof shear stiffness based on the values of peak force anddisplacement is defined as

119870ℎ

eff =

1003816100381610038161003816119865+1003816100381610038161003816+1003816100381610038161003816119865minus1003816100381610038161003816

|119889+| + |119889minus|

(1)

where 119889+ and 119889minus are the maximum positive and maximumnegative test displacements respectively and 119865+ and 119865minus arethe forces at instance of displacements 119889+ and 119889minus respectively[17] This stiffness is interpreted as the effective or overallstiffness of the bearing during the test This stiffness is usedto calculate the stored or elastic energy of the bearings duringcyclic tests

The hysteresis loops were also analyzed to obtain theequivalent viscous damping ratio of the bearing for eachtest A hysteresis loop represents the plot of force againstdisplacement and therefore the area contained within sucha loop represents the energy dissipated by the bearing

The equivalent viscous damping ratio exhibited by thebearing is evaluated in the usual structural engineeringfashion [18]

120585 =

119882119889

4120587119882119904

(2)

4 Shock and Vibration

(a) Testing system

(A) Push-pull steel plate(B) Bearings to be tested (two bearings are tested)(C) Hydraulic cylinder (for application of vertical loads)(D) Hydraulic cylinder (for application of horizontal loads)

(E) Load cell in the vertical direction(F) Load cell in the horizontal direction (G) LVDT

204

260

C

GAB

B

E

D D

2215

3847

1515

1533

70

F

4

128

178

(b) Schematic layout (dimensions cm)

Figure 2 General view of the horizontal shear test equipment

0 6 12 18 24 30 36 42

Hor

izon

tal s

trai

n (

)

Time (s)

Horizontal test signal for bearing

minus100

minus75

minus50

minus25

0

25

50

75

100

Figure 3 Input signal for horizontal shear test with 345MPa and690MPa vertical preload

where119882119889represents a dissipated energy equal to the hystere-

sis loop area and119882119904corresponds to stored or elastic energy

defined by the following formula

119882119904= 119870ℎ

eff119889max2

2

(3)

Here 119889max is the average of positive and negative maximumdisplacements and is defined as

119889max =

1003816100381610038161003816119889+1003816100381610038161003816+1003816100381610038161003816119889minus1003816100381610038161003816

2

(4)

Shock and Vibration 5

Table 2 Equivalent viscous damping values

Type and damp ratio

Equivalent viscous damping 120585 under vertical pressure (MPa)345 690

Strain level () Strain level ()25 50 100 Average 25 50 100 Average

1198781119910 116 108 136 12 86 10 96 941198651119910 107 107 109 108 75 82 98 85120585119904120585119891

109 101 125 111 115 123 098 1111198781119911 102 132 125 1197 67 92 109 8931198651119911 134 166 150 150 74 121 132 109120585119904120585119891

076 079 083 080 091 076 083 0821198782119910 84 116 132 1107 58 88 87 771198652119910 117 101 87 102 65 109 79 84120585119904120585119891

072 115 151 109 090 081 109 0921198782119911 74 113 143 110 53 78 124 851198652119911 94 104 89 96 6 91 76 76120585119904120585119891

079 109 159 115 088 086 162 1121198783119910 58 85 102 82 52 63 78 641198653119910 69 85 92 82 5 58 72 60120585119904120585119891

084 100 111 100 104 109 109 1071198783119911 85 69 77 77 51 5 63 551198653119911 6 78 8 73 57 55 75 62120585119904120585119891

142 089 097 106 088 090 084 0881198784119910 101 114 105 107 99 88 99 951198654119910 98 93 84 92 98 86 8 88120585119904120585119891

103 123 126 116 101 102 123 1081198784119911 97 103 88 96 97 81 95 911198654119911 108 101 97 102 10 87 84 90120585119904120585119891

090 102 091 094 098 093 114 101

The linear viscous model assumes that the energy dissipatedin each cycle is linear with the frequency and quadratic withthe displacement [18]

Dynamic response of an isolated structure dependsmainly on the horizontal stiffness of isolators The followingequation for horizontal stiffness 119870

ℎ is based on the simple

analysis that can be found in strength of material text booksand is used for both steel and fiber reinforcement conditionsalthough the equation is developed for elastomeric materials

119870ℎ=

119860119866

119879119903

(5)

where 119870ℎis horizontal stiffness of bearing (kNm) 119866 is

shear modulus of elastomer (MPa) 119879119903is total thickness of

elastomeric material (mm) and 119860 is plan area of the bearing(mm2)

3 Test Results and Discussion

Results of horizontal shear test are presented in this part InTable 2 a comparison of numerical values of the damping of

both types of bearings at different strain levels is presentedThe average damping of the bearing is the arithmetic meanof the damping values during all the cycles As it is clearfrom the presented results in Table 2 there is not thatmuch of difference between the average values of dampingpertaining to the fiber mesh- and steel-reinforced bearingsThemaximumdifference between the average damping ratiosis about 20 The main source of energy dissipation inthese elastomeric bearings is rubber compound and selectionof reinforcement material is believed not to result in bigdifference in damping valuesThedamping values in this kindof fiber- and steel-reinforced bearing are within reasonabletolerances

Horizontal effective stiffness test results of the bearingsare presented in Table 3 The horizontal stiffness of thesteel-reinforced bearings and that of fiber mesh-reinforcedbearings do not differ much for large size bearings whichhad higher stiffness compared to the small sizes as expectedLarger specimens are more stable to rollover due to theirgeometrical properties and high ratios of area to elastomerthickness and rollover starts at high levels of shear strain inthese bearings

6 Shock and Vibration

The same observation cannot be made for the small sizebearings due to the early rollover response of the fiber mesh-reinforced bearings that decreased the stiffness at larger strainvalues significantly as shown in Figures 4(a)ndash4(d) In all ofthe shear tests as strain level increases effective stiffness ofbearings decreases Increase in vertical preload resulted inhigher values of horizontal stiffness

For Type 1 bearings large size ones at lower strainlevels (up to 50) stiffness of fiber-reinforced bearings wasslightly greater than the steel-reinforced ones As strain levelincreases rollover of fiber-reinforced bearings commencedand this phenomenon led to a decrease in stiffness In Type 2bearings stiffness of fiber-reinforced bearings at lower strainlevels is greater than steel-reinforced ones but as rolloverstarts their stiffness decreases drastically For Types 3 and4 bearings decrease in stiffness developed at lower strainlevels This observation could be attributed to the small sizeof the bearings because rollover deformation is affected by theratio between the bearing thickness and base side length andbearings with smaller ratios have more potential to developrollover response than larger specimens In larger specimensrollover starts at larger levels of strain compared to small sizebearings In steel-reinforced bearings the same observationof rollover happens at larger strain levels compared to fiber-reinforced bearings The governing trend in the tested speci-mens is that as strain level increases the difference betweenthe effective stiffness of the steel-reinforced bearings andthat of fiber-reinforced bearings increases and the amountof increase depends on several parameters such as size andvertical pressure

The minimum divergence in stiffness of 1 is observedat high compressive stress levels for the bearings with largerplan area and thicker total elastomeric layers The maximumdivergence in stiffness of 78 is observed at low compressivestress levels for the small size bearing with lower totalthickness of elastomeric materials

The conventional horizontal stiffness presented in (5)has two components one being material property and theother being size The material property is presented by shearmodulus 119866 and the size index is presented by 119860119879

119903ratio

In all the tests the shear modulus 119866 is the same Thereforea relationship for size effect versus correction factor isdeveloped within this research The nonlinear relationshipbetween horizontal stiffness of steel-reinforced bearings andthat of fiber mesh-reinforced bearings can be represented by

119870(eff)119904

119870(eff)119891= 119891(

119860

119879119903

) = 120572 (6)

where119870(eff)119904 is horizontal effective stiffness of steel-reinforced

bearings119870(eff)119891 is horizontal effective stiffness of fiber mesh-

reinforced bearings and 120572 is nonlinear correction factor forsize effect

It has been experimentally determined that the 120572 factorcan be obtained from best fit curve using Figure 5

120572 = 609 (

119860

119879119903

)

minus023

(7)

Therefore the effective horizontal stiffness of fiber mesh-reinforced bearings can be recommended for 100 strain

119870(eff)119891 =

119866

609

(

119860

119879119903

)

123

119860

119879119903

le 3000 (8)

No correction is suggested for 119860119879119903

values exceeding3000mm2mm and the effective stiffness for elastomericmaterial in (5) can be applied to fiber mesh-reinforcedbearings For strain levels less than 100 linear interpolationfor the values given in Table 3 can be recommended to use

The proposed equation does not take account of theparticular rollover deformation of fiber-reinforced bearingsbut as in the studies by Kelly [19 20] for example theexpression for estimating the rollout stability limit changesby only 5 percent when the compression load is doubled Sothis equation can be used to determine the horizontal stiffnessof the fiber-reinforced bearings in the range of discussedpressures (345ndash690MPa)

Unbonded small size fiber-reinforced bearings candevelop very low horizontal stiffness compared to steel-reinforced bearings and this may be considered as anadvantage in design as long as rollover deformations of thebearings are stable It shall be noted that the rollover didnot develop any instability during tests The reason is thatall the specimens had curves with increasing resisting forceat an increase of the applied shear deformation No zero ornegative tangent stiffness was observed in test results andafter unloading there was not any residual deformation inthe bearings All the bearings sustained the applied loadand strain levels and no visible damage was developed inbearings as shown in Figure 6

It can be concluded that effective lateral stiffness of fiber-reinforced bearings is affected by several parameters suchas geometrical properties strain level and vertical preloadIt can be stated that rollover response of fiber-reinforcedbearing is beneficial if the bearing remains stable horizontally

Hysteresis loops obtained in horizontal shear test forselected bearings are plotted in terms of horizontal displace-ment versus horizontal load as shown in Figures 7(a)ndash7(d)In this figure horizontal axis corresponds to displacementof bearings (mm) and vertical axis corresponds to horizontalforce (kN) Horizontal stiffness for a single bearing is consid-ered to be the half of the values since the tests are conductedsimultaneously on two bearings

4 Conclusion

Test results of new types of fiber mesh-reinforced elastomericbearings and conventional isolators are comparedThe obser-vations made during the tests can be summarized as follows

(i) The conventional horizontal stiffness used in designof elastomeric materials does not always apply to thefibermesh-reinforced bearings At high levels of shearstrain there is a significant deviation in horizontalstiffness of small size fiber mesh-reinforced bearingscompared to steel-reinforced bearings A nonlinear

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

4 Shock and Vibration

(a) Testing system

(A) Push-pull steel plate(B) Bearings to be tested (two bearings are tested)(C) Hydraulic cylinder (for application of vertical loads)(D) Hydraulic cylinder (for application of horizontal loads)

(E) Load cell in the vertical direction(F) Load cell in the horizontal direction (G) LVDT

204

260

C

GAB

B

E

D D

2215

3847

1515

1533

70

F

4

128

178

(b) Schematic layout (dimensions cm)

Figure 2 General view of the horizontal shear test equipment

0 6 12 18 24 30 36 42

Hor

izon

tal s

trai

n (

)

Time (s)

Horizontal test signal for bearing

minus100

minus75

minus50

minus25

0

25

50

75

100

Figure 3 Input signal for horizontal shear test with 345MPa and690MPa vertical preload

where119882119889represents a dissipated energy equal to the hystere-

sis loop area and119882119904corresponds to stored or elastic energy

defined by the following formula

119882119904= 119870ℎ

eff119889max2

2

(3)

Here 119889max is the average of positive and negative maximumdisplacements and is defined as

119889max =

1003816100381610038161003816119889+1003816100381610038161003816+1003816100381610038161003816119889minus1003816100381610038161003816

2

(4)

Shock and Vibration 5

Table 2 Equivalent viscous damping values

Type and damp ratio

Equivalent viscous damping 120585 under vertical pressure (MPa)345 690

Strain level () Strain level ()25 50 100 Average 25 50 100 Average

1198781119910 116 108 136 12 86 10 96 941198651119910 107 107 109 108 75 82 98 85120585119904120585119891

109 101 125 111 115 123 098 1111198781119911 102 132 125 1197 67 92 109 8931198651119911 134 166 150 150 74 121 132 109120585119904120585119891

076 079 083 080 091 076 083 0821198782119910 84 116 132 1107 58 88 87 771198652119910 117 101 87 102 65 109 79 84120585119904120585119891

072 115 151 109 090 081 109 0921198782119911 74 113 143 110 53 78 124 851198652119911 94 104 89 96 6 91 76 76120585119904120585119891

079 109 159 115 088 086 162 1121198783119910 58 85 102 82 52 63 78 641198653119910 69 85 92 82 5 58 72 60120585119904120585119891

084 100 111 100 104 109 109 1071198783119911 85 69 77 77 51 5 63 551198653119911 6 78 8 73 57 55 75 62120585119904120585119891

142 089 097 106 088 090 084 0881198784119910 101 114 105 107 99 88 99 951198654119910 98 93 84 92 98 86 8 88120585119904120585119891

103 123 126 116 101 102 123 1081198784119911 97 103 88 96 97 81 95 911198654119911 108 101 97 102 10 87 84 90120585119904120585119891

090 102 091 094 098 093 114 101

The linear viscous model assumes that the energy dissipatedin each cycle is linear with the frequency and quadratic withthe displacement [18]

Dynamic response of an isolated structure dependsmainly on the horizontal stiffness of isolators The followingequation for horizontal stiffness 119870

ℎ is based on the simple

analysis that can be found in strength of material text booksand is used for both steel and fiber reinforcement conditionsalthough the equation is developed for elastomeric materials

119870ℎ=

119860119866

119879119903

(5)

where 119870ℎis horizontal stiffness of bearing (kNm) 119866 is

shear modulus of elastomer (MPa) 119879119903is total thickness of

elastomeric material (mm) and 119860 is plan area of the bearing(mm2)

3 Test Results and Discussion

Results of horizontal shear test are presented in this part InTable 2 a comparison of numerical values of the damping of

both types of bearings at different strain levels is presentedThe average damping of the bearing is the arithmetic meanof the damping values during all the cycles As it is clearfrom the presented results in Table 2 there is not thatmuch of difference between the average values of dampingpertaining to the fiber mesh- and steel-reinforced bearingsThemaximumdifference between the average damping ratiosis about 20 The main source of energy dissipation inthese elastomeric bearings is rubber compound and selectionof reinforcement material is believed not to result in bigdifference in damping valuesThedamping values in this kindof fiber- and steel-reinforced bearing are within reasonabletolerances

Horizontal effective stiffness test results of the bearingsare presented in Table 3 The horizontal stiffness of thesteel-reinforced bearings and that of fiber mesh-reinforcedbearings do not differ much for large size bearings whichhad higher stiffness compared to the small sizes as expectedLarger specimens are more stable to rollover due to theirgeometrical properties and high ratios of area to elastomerthickness and rollover starts at high levels of shear strain inthese bearings

6 Shock and Vibration

The same observation cannot be made for the small sizebearings due to the early rollover response of the fiber mesh-reinforced bearings that decreased the stiffness at larger strainvalues significantly as shown in Figures 4(a)ndash4(d) In all ofthe shear tests as strain level increases effective stiffness ofbearings decreases Increase in vertical preload resulted inhigher values of horizontal stiffness

For Type 1 bearings large size ones at lower strainlevels (up to 50) stiffness of fiber-reinforced bearings wasslightly greater than the steel-reinforced ones As strain levelincreases rollover of fiber-reinforced bearings commencedand this phenomenon led to a decrease in stiffness In Type 2bearings stiffness of fiber-reinforced bearings at lower strainlevels is greater than steel-reinforced ones but as rolloverstarts their stiffness decreases drastically For Types 3 and4 bearings decrease in stiffness developed at lower strainlevels This observation could be attributed to the small sizeof the bearings because rollover deformation is affected by theratio between the bearing thickness and base side length andbearings with smaller ratios have more potential to developrollover response than larger specimens In larger specimensrollover starts at larger levels of strain compared to small sizebearings In steel-reinforced bearings the same observationof rollover happens at larger strain levels compared to fiber-reinforced bearings The governing trend in the tested speci-mens is that as strain level increases the difference betweenthe effective stiffness of the steel-reinforced bearings andthat of fiber-reinforced bearings increases and the amountof increase depends on several parameters such as size andvertical pressure

The minimum divergence in stiffness of 1 is observedat high compressive stress levels for the bearings with largerplan area and thicker total elastomeric layers The maximumdivergence in stiffness of 78 is observed at low compressivestress levels for the small size bearing with lower totalthickness of elastomeric materials

The conventional horizontal stiffness presented in (5)has two components one being material property and theother being size The material property is presented by shearmodulus 119866 and the size index is presented by 119860119879

119903ratio

In all the tests the shear modulus 119866 is the same Thereforea relationship for size effect versus correction factor isdeveloped within this research The nonlinear relationshipbetween horizontal stiffness of steel-reinforced bearings andthat of fiber mesh-reinforced bearings can be represented by

119870(eff)119904

119870(eff)119891= 119891(

119860

119879119903

) = 120572 (6)

where119870(eff)119904 is horizontal effective stiffness of steel-reinforced

bearings119870(eff)119891 is horizontal effective stiffness of fiber mesh-

reinforced bearings and 120572 is nonlinear correction factor forsize effect

It has been experimentally determined that the 120572 factorcan be obtained from best fit curve using Figure 5

120572 = 609 (

119860

119879119903

)

minus023

(7)

Therefore the effective horizontal stiffness of fiber mesh-reinforced bearings can be recommended for 100 strain

119870(eff)119891 =

119866

609

(

119860

119879119903

)

123

119860

119879119903

le 3000 (8)

No correction is suggested for 119860119879119903

values exceeding3000mm2mm and the effective stiffness for elastomericmaterial in (5) can be applied to fiber mesh-reinforcedbearings For strain levels less than 100 linear interpolationfor the values given in Table 3 can be recommended to use

The proposed equation does not take account of theparticular rollover deformation of fiber-reinforced bearingsbut as in the studies by Kelly [19 20] for example theexpression for estimating the rollout stability limit changesby only 5 percent when the compression load is doubled Sothis equation can be used to determine the horizontal stiffnessof the fiber-reinforced bearings in the range of discussedpressures (345ndash690MPa)

Unbonded small size fiber-reinforced bearings candevelop very low horizontal stiffness compared to steel-reinforced bearings and this may be considered as anadvantage in design as long as rollover deformations of thebearings are stable It shall be noted that the rollover didnot develop any instability during tests The reason is thatall the specimens had curves with increasing resisting forceat an increase of the applied shear deformation No zero ornegative tangent stiffness was observed in test results andafter unloading there was not any residual deformation inthe bearings All the bearings sustained the applied loadand strain levels and no visible damage was developed inbearings as shown in Figure 6

It can be concluded that effective lateral stiffness of fiber-reinforced bearings is affected by several parameters suchas geometrical properties strain level and vertical preloadIt can be stated that rollover response of fiber-reinforcedbearing is beneficial if the bearing remains stable horizontally

Hysteresis loops obtained in horizontal shear test forselected bearings are plotted in terms of horizontal displace-ment versus horizontal load as shown in Figures 7(a)ndash7(d)In this figure horizontal axis corresponds to displacementof bearings (mm) and vertical axis corresponds to horizontalforce (kN) Horizontal stiffness for a single bearing is consid-ered to be the half of the values since the tests are conductedsimultaneously on two bearings

4 Conclusion

Test results of new types of fiber mesh-reinforced elastomericbearings and conventional isolators are comparedThe obser-vations made during the tests can be summarized as follows

(i) The conventional horizontal stiffness used in designof elastomeric materials does not always apply to thefibermesh-reinforced bearings At high levels of shearstrain there is a significant deviation in horizontalstiffness of small size fiber mesh-reinforced bearingscompared to steel-reinforced bearings A nonlinear

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

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Active and Passive Electronic Components

Control Scienceand Engineering

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RotatingMachinery

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Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

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Volume 2014

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SensorsJournal of

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Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

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DistributedSensor Networks

International Journal of

Shock and Vibration 5

Table 2 Equivalent viscous damping values

Type and damp ratio

Equivalent viscous damping 120585 under vertical pressure (MPa)345 690

Strain level () Strain level ()25 50 100 Average 25 50 100 Average

1198781119910 116 108 136 12 86 10 96 941198651119910 107 107 109 108 75 82 98 85120585119904120585119891

109 101 125 111 115 123 098 1111198781119911 102 132 125 1197 67 92 109 8931198651119911 134 166 150 150 74 121 132 109120585119904120585119891

076 079 083 080 091 076 083 0821198782119910 84 116 132 1107 58 88 87 771198652119910 117 101 87 102 65 109 79 84120585119904120585119891

072 115 151 109 090 081 109 0921198782119911 74 113 143 110 53 78 124 851198652119911 94 104 89 96 6 91 76 76120585119904120585119891

079 109 159 115 088 086 162 1121198783119910 58 85 102 82 52 63 78 641198653119910 69 85 92 82 5 58 72 60120585119904120585119891

084 100 111 100 104 109 109 1071198783119911 85 69 77 77 51 5 63 551198653119911 6 78 8 73 57 55 75 62120585119904120585119891

142 089 097 106 088 090 084 0881198784119910 101 114 105 107 99 88 99 951198654119910 98 93 84 92 98 86 8 88120585119904120585119891

103 123 126 116 101 102 123 1081198784119911 97 103 88 96 97 81 95 911198654119911 108 101 97 102 10 87 84 90120585119904120585119891

090 102 091 094 098 093 114 101

The linear viscous model assumes that the energy dissipatedin each cycle is linear with the frequency and quadratic withthe displacement [18]

Dynamic response of an isolated structure dependsmainly on the horizontal stiffness of isolators The followingequation for horizontal stiffness 119870

ℎ is based on the simple

analysis that can be found in strength of material text booksand is used for both steel and fiber reinforcement conditionsalthough the equation is developed for elastomeric materials

119870ℎ=

119860119866

119879119903

(5)

where 119870ℎis horizontal stiffness of bearing (kNm) 119866 is

shear modulus of elastomer (MPa) 119879119903is total thickness of

elastomeric material (mm) and 119860 is plan area of the bearing(mm2)

3 Test Results and Discussion

Results of horizontal shear test are presented in this part InTable 2 a comparison of numerical values of the damping of

both types of bearings at different strain levels is presentedThe average damping of the bearing is the arithmetic meanof the damping values during all the cycles As it is clearfrom the presented results in Table 2 there is not thatmuch of difference between the average values of dampingpertaining to the fiber mesh- and steel-reinforced bearingsThemaximumdifference between the average damping ratiosis about 20 The main source of energy dissipation inthese elastomeric bearings is rubber compound and selectionof reinforcement material is believed not to result in bigdifference in damping valuesThedamping values in this kindof fiber- and steel-reinforced bearing are within reasonabletolerances

Horizontal effective stiffness test results of the bearingsare presented in Table 3 The horizontal stiffness of thesteel-reinforced bearings and that of fiber mesh-reinforcedbearings do not differ much for large size bearings whichhad higher stiffness compared to the small sizes as expectedLarger specimens are more stable to rollover due to theirgeometrical properties and high ratios of area to elastomerthickness and rollover starts at high levels of shear strain inthese bearings

6 Shock and Vibration

The same observation cannot be made for the small sizebearings due to the early rollover response of the fiber mesh-reinforced bearings that decreased the stiffness at larger strainvalues significantly as shown in Figures 4(a)ndash4(d) In all ofthe shear tests as strain level increases effective stiffness ofbearings decreases Increase in vertical preload resulted inhigher values of horizontal stiffness

For Type 1 bearings large size ones at lower strainlevels (up to 50) stiffness of fiber-reinforced bearings wasslightly greater than the steel-reinforced ones As strain levelincreases rollover of fiber-reinforced bearings commencedand this phenomenon led to a decrease in stiffness In Type 2bearings stiffness of fiber-reinforced bearings at lower strainlevels is greater than steel-reinforced ones but as rolloverstarts their stiffness decreases drastically For Types 3 and4 bearings decrease in stiffness developed at lower strainlevels This observation could be attributed to the small sizeof the bearings because rollover deformation is affected by theratio between the bearing thickness and base side length andbearings with smaller ratios have more potential to developrollover response than larger specimens In larger specimensrollover starts at larger levels of strain compared to small sizebearings In steel-reinforced bearings the same observationof rollover happens at larger strain levels compared to fiber-reinforced bearings The governing trend in the tested speci-mens is that as strain level increases the difference betweenthe effective stiffness of the steel-reinforced bearings andthat of fiber-reinforced bearings increases and the amountof increase depends on several parameters such as size andvertical pressure

The minimum divergence in stiffness of 1 is observedat high compressive stress levels for the bearings with largerplan area and thicker total elastomeric layers The maximumdivergence in stiffness of 78 is observed at low compressivestress levels for the small size bearing with lower totalthickness of elastomeric materials

The conventional horizontal stiffness presented in (5)has two components one being material property and theother being size The material property is presented by shearmodulus 119866 and the size index is presented by 119860119879

119903ratio

In all the tests the shear modulus 119866 is the same Thereforea relationship for size effect versus correction factor isdeveloped within this research The nonlinear relationshipbetween horizontal stiffness of steel-reinforced bearings andthat of fiber mesh-reinforced bearings can be represented by

119870(eff)119904

119870(eff)119891= 119891(

119860

119879119903

) = 120572 (6)

where119870(eff)119904 is horizontal effective stiffness of steel-reinforced

bearings119870(eff)119891 is horizontal effective stiffness of fiber mesh-

reinforced bearings and 120572 is nonlinear correction factor forsize effect

It has been experimentally determined that the 120572 factorcan be obtained from best fit curve using Figure 5

120572 = 609 (

119860

119879119903

)

minus023

(7)

Therefore the effective horizontal stiffness of fiber mesh-reinforced bearings can be recommended for 100 strain

119870(eff)119891 =

119866

609

(

119860

119879119903

)

123

119860

119879119903

le 3000 (8)

No correction is suggested for 119860119879119903

values exceeding3000mm2mm and the effective stiffness for elastomericmaterial in (5) can be applied to fiber mesh-reinforcedbearings For strain levels less than 100 linear interpolationfor the values given in Table 3 can be recommended to use

The proposed equation does not take account of theparticular rollover deformation of fiber-reinforced bearingsbut as in the studies by Kelly [19 20] for example theexpression for estimating the rollout stability limit changesby only 5 percent when the compression load is doubled Sothis equation can be used to determine the horizontal stiffnessof the fiber-reinforced bearings in the range of discussedpressures (345ndash690MPa)

Unbonded small size fiber-reinforced bearings candevelop very low horizontal stiffness compared to steel-reinforced bearings and this may be considered as anadvantage in design as long as rollover deformations of thebearings are stable It shall be noted that the rollover didnot develop any instability during tests The reason is thatall the specimens had curves with increasing resisting forceat an increase of the applied shear deformation No zero ornegative tangent stiffness was observed in test results andafter unloading there was not any residual deformation inthe bearings All the bearings sustained the applied loadand strain levels and no visible damage was developed inbearings as shown in Figure 6

It can be concluded that effective lateral stiffness of fiber-reinforced bearings is affected by several parameters suchas geometrical properties strain level and vertical preloadIt can be stated that rollover response of fiber-reinforcedbearing is beneficial if the bearing remains stable horizontally

Hysteresis loops obtained in horizontal shear test forselected bearings are plotted in terms of horizontal displace-ment versus horizontal load as shown in Figures 7(a)ndash7(d)In this figure horizontal axis corresponds to displacementof bearings (mm) and vertical axis corresponds to horizontalforce (kN) Horizontal stiffness for a single bearing is consid-ered to be the half of the values since the tests are conductedsimultaneously on two bearings

4 Conclusion

Test results of new types of fiber mesh-reinforced elastomericbearings and conventional isolators are comparedThe obser-vations made during the tests can be summarized as follows

(i) The conventional horizontal stiffness used in designof elastomeric materials does not always apply to thefibermesh-reinforced bearings At high levels of shearstrain there is a significant deviation in horizontalstiffness of small size fiber mesh-reinforced bearingscompared to steel-reinforced bearings A nonlinear

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

6 Shock and Vibration

The same observation cannot be made for the small sizebearings due to the early rollover response of the fiber mesh-reinforced bearings that decreased the stiffness at larger strainvalues significantly as shown in Figures 4(a)ndash4(d) In all ofthe shear tests as strain level increases effective stiffness ofbearings decreases Increase in vertical preload resulted inhigher values of horizontal stiffness

For Type 1 bearings large size ones at lower strainlevels (up to 50) stiffness of fiber-reinforced bearings wasslightly greater than the steel-reinforced ones As strain levelincreases rollover of fiber-reinforced bearings commencedand this phenomenon led to a decrease in stiffness In Type 2bearings stiffness of fiber-reinforced bearings at lower strainlevels is greater than steel-reinforced ones but as rolloverstarts their stiffness decreases drastically For Types 3 and4 bearings decrease in stiffness developed at lower strainlevels This observation could be attributed to the small sizeof the bearings because rollover deformation is affected by theratio between the bearing thickness and base side length andbearings with smaller ratios have more potential to developrollover response than larger specimens In larger specimensrollover starts at larger levels of strain compared to small sizebearings In steel-reinforced bearings the same observationof rollover happens at larger strain levels compared to fiber-reinforced bearings The governing trend in the tested speci-mens is that as strain level increases the difference betweenthe effective stiffness of the steel-reinforced bearings andthat of fiber-reinforced bearings increases and the amountof increase depends on several parameters such as size andvertical pressure

The minimum divergence in stiffness of 1 is observedat high compressive stress levels for the bearings with largerplan area and thicker total elastomeric layers The maximumdivergence in stiffness of 78 is observed at low compressivestress levels for the small size bearing with lower totalthickness of elastomeric materials

The conventional horizontal stiffness presented in (5)has two components one being material property and theother being size The material property is presented by shearmodulus 119866 and the size index is presented by 119860119879

119903ratio

In all the tests the shear modulus 119866 is the same Thereforea relationship for size effect versus correction factor isdeveloped within this research The nonlinear relationshipbetween horizontal stiffness of steel-reinforced bearings andthat of fiber mesh-reinforced bearings can be represented by

119870(eff)119904

119870(eff)119891= 119891(

119860

119879119903

) = 120572 (6)

where119870(eff)119904 is horizontal effective stiffness of steel-reinforced

bearings119870(eff)119891 is horizontal effective stiffness of fiber mesh-

reinforced bearings and 120572 is nonlinear correction factor forsize effect

It has been experimentally determined that the 120572 factorcan be obtained from best fit curve using Figure 5

120572 = 609 (

119860

119879119903

)

minus023

(7)

Therefore the effective horizontal stiffness of fiber mesh-reinforced bearings can be recommended for 100 strain

119870(eff)119891 =

119866

609

(

119860

119879119903

)

123

119860

119879119903

le 3000 (8)

No correction is suggested for 119860119879119903

values exceeding3000mm2mm and the effective stiffness for elastomericmaterial in (5) can be applied to fiber mesh-reinforcedbearings For strain levels less than 100 linear interpolationfor the values given in Table 3 can be recommended to use

The proposed equation does not take account of theparticular rollover deformation of fiber-reinforced bearingsbut as in the studies by Kelly [19 20] for example theexpression for estimating the rollout stability limit changesby only 5 percent when the compression load is doubled Sothis equation can be used to determine the horizontal stiffnessof the fiber-reinforced bearings in the range of discussedpressures (345ndash690MPa)

Unbonded small size fiber-reinforced bearings candevelop very low horizontal stiffness compared to steel-reinforced bearings and this may be considered as anadvantage in design as long as rollover deformations of thebearings are stable It shall be noted that the rollover didnot develop any instability during tests The reason is thatall the specimens had curves with increasing resisting forceat an increase of the applied shear deformation No zero ornegative tangent stiffness was observed in test results andafter unloading there was not any residual deformation inthe bearings All the bearings sustained the applied loadand strain levels and no visible damage was developed inbearings as shown in Figure 6

It can be concluded that effective lateral stiffness of fiber-reinforced bearings is affected by several parameters suchas geometrical properties strain level and vertical preloadIt can be stated that rollover response of fiber-reinforcedbearing is beneficial if the bearing remains stable horizontally

Hysteresis loops obtained in horizontal shear test forselected bearings are plotted in terms of horizontal displace-ment versus horizontal load as shown in Figures 7(a)ndash7(d)In this figure horizontal axis corresponds to displacementof bearings (mm) and vertical axis corresponds to horizontalforce (kN) Horizontal stiffness for a single bearing is consid-ered to be the half of the values since the tests are conductedsimultaneously on two bearings

4 Conclusion

Test results of new types of fiber mesh-reinforced elastomericbearings and conventional isolators are comparedThe obser-vations made during the tests can be summarized as follows

(i) The conventional horizontal stiffness used in designof elastomeric materials does not always apply to thefibermesh-reinforced bearings At high levels of shearstrain there is a significant deviation in horizontalstiffness of small size fiber mesh-reinforced bearingscompared to steel-reinforced bearings A nonlinear

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Shock and Vibration 7

08

085

09

095

1

105

11

0 25 50 75 100Strain level ()

Effective stiffness comparison type 1

1y-345MPa1y-690MPa

1z-345MPa1z-690MPa

K(e

ff)sK

(eff)f

(a) Type 1 bearings (119870eff)s(119870eff)f versus shear strain

Effective stiffness comparison type 2

094

096

098

1

102

104

106

108

11

0 25 50 75 100Strain level ()

2y-345MPa2y-690MPa

2z-345MPa2z-690MPa

K(e

ff)sK

(eff)f

(b) Type 2 bearings (119870eff)s(119870eff)f versus shear strain

08

1

12

14

16

0 25 50 75 100Strain level ()

Effective stiffness comparison type 3

3y-345MPa3y-690MPa

3z-345MPa3z-690MPa

K(e

ff)sK

(eff)f

(c) Type 3 bearings (119870eff)s(119870eff)f versus shear strain

1

12

14

16

18

2

0 25 50 75 100Strain level ()

Effective stiffness comparison type 4

4y-345MPa4y-690MPa

4z-345MPa4z-690MPa

K(e

ff)sK

(eff)f

(d) Type 4 bearings (119870eff)s(119870eff)f versus shear strain

Figure 4 Comparison of effective stiffness of steel-reinforced and fiber-reinforced bearings

002040608

112141618

0 500 1000 1500 2000 2500 3000 3500

y = 60934xminus0232

R2 = 08412

ATr (mm2mm)

120572=K(e

ff)sK

(eff)f

Figure 5 Suggested correction factor for horizontal stiffness forfiber mesh-reinforced bearings at 100 strain level

equation is suggested as a correction factor for fiber-reinforced bearing horizontal stiffness computationsto account for this divergence

(ii) The tests under different compressive loads revealedthat the horizontal stiffness slightly increases underhigh compressive loads and proposed correction fac-tor can be applied for both investigated cases in thisresearch within a reasonable tolerance

(iii) Damping values in both fiber- and steel-reinforcedbearings are similar since the same elastomericmaterial is used in both reinforcement conditionsDamping is typically provided by the selection ofelastomeric material

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

8 Shock and Vibration

(a) Unbonded 1198654119910 at 100 strain (b) Unbonded 1198784119910 at 100 strain

Figure 6 Deformation mode shape of fiber mesh-reinforced bearings

Table 3 Effective stiffness values

Type and stiffness ratio

Effective stiffness 119870ℎeff (kNm)Vertical pressure (MPa)

345 690Strain level () Strain level ()

25 50 100 25 50 1001198781119910 2221 1866 1619 2363 1995 18221198651119910 2383 1931 1633 2730 2187 1827119870119904119870119891

093 097 099 086 091 0991198781119911 3438 2725 2387 3787 3005 26331198651119911 3674 2708 2278 4164 3326 2663119870119904119870119891

094 101 105 091 090 0991198782119910 2519 2086 1784 2772 2307 21331198652119910 2347 2053 1865 2757 2296 2080119870119904119870119891

107 102 096 101 101 1021198782119911 2962 2420 2035 3270 2755 24201198652119911 2737 2256 2135 3180 2602 2374119870119904119870119891

108 107 095 103 106 1021198783119910 944 762 657 918 793 7071198653119910 811 656 548 898 751 617119870119904119870119891

116 116 120 102 106 1151198783119911 669 559 507 716 609 5621198653119911 582 472 371 615 508 395119870119904119870119891

115 118 137 116 120 1421198784119910 570 440 429 595 472 4451198654119910 464 358 306 485 375 321119870119904119870119891

123 123 140 122 125 1391198784119911 725 581 558 769 612 5371198654119911 543 414 313 535 415 323119870119904119870119891

133 140 178 144 147 16

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

Shock and Vibration 9

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(a) 1198651119910 under 690MPa vertical preload

050

100150200

0 20 40 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus60 minus20

minus200

minus150

minus100

minus50

(b) 1198781119910 under 690MPa vertical preload

010203040

0 10 20 30 40 50 60

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus30minus20minus10

(c) 1198654119910 under 345MPa vertical preload

01020304050

0 10 20 30 40 50

Hor

izon

tal l

oad

(kN

)

Horizontal displacement (mm)

minus40minus50minus60 minus30 minus20 minus10

minus40minus50

minus30minus20minus10

(d) 1198784119910 under 345MPa vertical preload

Figure 7 Horizontal shear test results for some of the specimens (horizontal load versus horizontal displacement for a pair of bearings)

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors would like to thank the Middle East Tech-nical University (BAP-03 03 2012 003) and TUBITAK(KAMAG 110G093) for their financial support Furthermorethe authors would like to acknowledge the Ozdekan KaucukA S (Ankara Turkey) and Maurer Sohne Group (IzmirTurkey) for preparation and production of test specimensThe authors would also like to extend their thanks to GeneralDirectorate of Turkish Highways (KGM)

References

[1] J M Kelly ldquoAnalysis of fiber-reinforced elastomeric isolatorsrdquoJournal of Seismology and Earthquake Engineering vol 2 no 1pp 19ndash34 1999

[2] B-Y Moon G-J Kang B-S Kang and J M Kelly ldquoDesignand manufacturing of fiber reinforced elastomeric isolator forseismic isolationrdquo Journal of Materials Processing Technologyvol 130-131 pp 145ndash150 2002

[3] G D Ashkezari A A Aghakouchak and M Kokabi ldquoDesignmanufacturing and evaluation of the performance of steellike fiber reinforced elastomeric seismic isolatorsrdquo Journal ofMaterials Processing Technology vol 197 no 1ndash3 pp 140ndash1502008

[4] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoLateralresponse evaluation of fiber-reinforced neoprene seismic isola-tors utilized in an unbonded applicationrdquo Journal of StructuralEngineering vol 134 no 10 pp 1627ndash1637 2008

[5] H Toopchi-Nezhad M J Tait and R G Drysdale ldquoShaketable study on an ordinary low-rise building seismically isolated

with SU-FREIs (stable unbonded-fiber reinforced elastomericisolators)rdquo Earthquake Engineering and Structural Dynamicsvol 38 no 11 pp 1335ndash1357 2009

[6] H Zhang T Peng J Li andW Li ldquoExperimental study of FRPrubber bearingrdquo Advanced Materials Research vol 168ndash170 pp1621ndash1624 2011

[7] A Calabrese and J M Kelly ldquoMechanics of fiber reinforcedbearingsrdquo PEER Report University of California BerkeleyCalif USA 2012

[8] G Russo M Pauletta and A Cortesia ldquoA study on experi-mental shear behavior of fiber-reinforced elastomeric isolatorswith various fiber layouts elastomers and aging conditionsrdquoEngineering Structures vol 52 pp 422ndash433 2013

[9] F Hedayati Dezfuli and M S Alam ldquoMulti-criteria optimiza-tion and seismic performance assessment of carbon FRP-basedelastomeric isolatorrdquo Engineering Structures vol 49 pp 525ndash540 2013

[10] A Karimzadeh Naghshineh U Akyuz and A Caner ldquoCom-parison of fundamental properties of new types of fiber-mesh-reinforced seismic isolators with conventional isolatorsrdquoEarthquake Engineering and Structural Dynamics vol 43 no 2pp 301ndash316 2014

[11] H Toopchi-Nezhad ldquoHorizontal stiffness solutions forunbonded fiber reinforced elastomeric bearingsrdquo StructuralEngineering and Mechanics vol 49 no 3 pp 395ndash410 2014

[12] J M Kelly and S M Takhirov ldquoAnalytical and experimentalstudy of fiber reinforced strip isolatorsrdquo PEER Report Univer-sity of California Berkeley Calif USA 2002

[13] G Russo andM Pauletta ldquoSliding instability of fiber-reinforcedelastomeric isolators in unbonded applicationsrdquo EngineeringStructures vol 48 pp 70ndash80 2013

[14] S Pinarbasi U Akyuz andGOzdemir ldquoAn experimental studyon low temperature behavior of elastomeric bridge bearingrdquo inProceedings of the 10th World Conference on Seismic IsolationEnergy Dissipation and Active Vibrations Control of StructuresIstanbul Turkey May 2007

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

10 Shock and Vibration

[15] C Ozkaya U Akyuz A Caner M Dicleli and S PinarbasildquoDevelopment of a new rubber seismic isolator lsquoBall Rub-ber Bearing (BRB)rsquordquo Earthquake Engineering and StructuralDynamics vol 40 no 12 pp 1337ndash1352 2011

[16] A Caner A K Naghshineh and S Erdal ldquoPerformance ofball rubber bearings in low-temperature regionsrdquo Journal ofPerformance of Constructed Facilities Article ID 040140602013

[17] AASHTO Guide Specifications for Seismic Isolation DesignAmerican Association of State Highway and TransportationOfficials Washington DC USA 2nd edition 2000

[18] A K Chopra Dynamics of Structures Theory and Applicationsto Earthquake Engineering Prentice Hall Upper Saddle RiverNJ USA 2nd edition 2007

[19] J M Kelly ldquoBuckling behaviour of elastomeric bearingsrdquo inEarthquake-Resistant Design with Rubber Springer LondonUK 2nd edition 1997

[20] M Imbimbo and J M Kelly ldquoStability aspects of elastomericisolatorsrdquo Earthquake Spectra vol 13 no 3 pp 431ndash449 1997

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

Propagation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Navigation and Observation

International Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

International Journal of

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Active and Passive Electronic Components

Control Scienceand Engineering

Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

RotatingMachinery

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Shock and Vibration

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Civil EngineeringAdvances in

Acoustics and VibrationAdvances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Electrical and Computer Engineering

Journal of

Advances inOptoElectronics

Hindawi Publishing Corporation httpwwwhindawicom

Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Chemical EngineeringInternational Journal of Antennas and

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

DistributedSensor Networks

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