Special Issue Article Journal of Intelligent Material Systems and Structures 2015, Vol. 26(14) 1818–1825 Ó The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1045389X15577654 jim.sagepub.com A laminated magnetorheological elastomer bearing prototype for seismic mitigation of bridge superstructures Zhi-Wei Xing, Miao Yu, Jie Fu, Yuan Wang and Lu-Jie Zhao Abstract In this article, an adaptive magnetorheological elastomer bearing prototype for seismic mitigation of bridge superstruc- tures is designed and manufactured. The magnetorheological elastomer bearing is developed featuring conventional lami- nated structure in the seismic rubber bearing. Besides, the magnetic circuit design of the laminated magnetorheological elastomer bearing is verified by electromagnetic analysis, and a base-isolated testing system is established to obtain the acceleration transmissibility under various applied currents. The experimental results indicate that the resonance fre- quency of the integrated system can be tuned from 10 to 20 Hz, and the transmissibility peak value reduces 20.67% simultaneously, for which the proposed bearing can be used for seismic mitigation. Finally, the stiffness and damping of the laminated magnetorheological elastomer bearing integrated vibration mitigation system are identified by the response characteristics. Keywords Magnetorheological elastomers, vibration mitigation, resonance frequency shift, parameter identification Introduction The widespread construction of railroad and highway bridges has drawn an increased attention in seismic isola- tion bearings as supports of the bridges. As a result of employing the seismic isolation bearings, the superstruc- tures’ motion is decoupled from the bridge piers’ motion during external excitations (such as earthquakes), thus reducing the transmitted acceleration by energy dissipa- tion in the isolator, as shown in Figure 1(a). Nevertheless, conventional laminated rubber bearings are unable to alter their performance due to the passive nature of tradi- tional rubber (Tyleri, 1991). As one of the most potential alternative solution, the ‘‘smart’’ semi-active vibration iso- lators with adjustable damping and stiffness are intended to mitigate the destructive vibration (Nagarajaiah and Sahasrabudhe, 2006; Ramallo et al., 2002; Yi et al., 2001; Yoshioka et al., 2002). In addition, variable damping and stiffness isolators, as shown in Figure 1(b), are able to achieve shift in resonance frequency and attenuation in transmissibility peak value by changing the properties of the isolation system (Behrooz et al., 2011; Dyke et al., 1996). Magnetorheological elastomers (MREs) mainly con- sist of micro-sized magnetic ferromagnetic particles dispersed in a polymer matrix (Gong et al., 2005; Jolly et al., 1996). MREs belong to a semi-active smart mate- rial that could vary its rheological, mechanical, and magnetic properties continuously, rapidly, and reversi- bly under an applied magnetic field (Ginder et al., 1999; Shen et al., 2004; Zhou, 2003). Owing to the field- dependent damping and stiffness, the MREs have an advantage in developing the semi-active controllable base isolators (Li et al., 2013a; Yang et al., 2015). Recently, several attempts have been made to develop MRE-based semi-active isolation systems for anti- seismic structures (Koo et al., 2009). Eem et al. (2011) investigated the feasibility of MRE-based isolation sys- tem by numerical evaluation, while Jung et al. (2011) corroborated that the smart base-isolation system out- performs the passive-type base-isolation system through Key Laboratory of Opto-electronic Technology and Systems, Ministry of Education of China, College of Optoelectronic Engineering, Chongqing University, Chongqing, China Corresponding author: Miao Yu, Key Laboratory of Opto-electronic Technology and Systems, Ministry of Education of China, College of Optoelectronic Engineering, Chongqing University, Chongqing 400044, China. Email: [email protected]at Chongqing University on November 23, 2015 jim.sagepub.com Downloaded from
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Special Issue Article
Journal of Intelligent Material Systemsand Structures2015, Vol. 26(14) 1818–1825� The Author(s) 2015Reprints and permissions:sagepub.co.uk/journalsPermissions.navDOI: 10.1177/1045389X15577654jim.sagepub.com
A laminated magnetorheologicalelastomer bearing prototype forseismic mitigation of bridgesuperstructures
Zhi-Wei Xing, Miao Yu, Jie Fu, Yuan Wang and Lu-Jie Zhao
AbstractIn this article, an adaptive magnetorheological elastomer bearing prototype for seismic mitigation of bridge superstruc-tures is designed and manufactured. The magnetorheological elastomer bearing is developed featuring conventional lami-nated structure in the seismic rubber bearing. Besides, the magnetic circuit design of the laminated magnetorheologicalelastomer bearing is verified by electromagnetic analysis, and a base-isolated testing system is established to obtain theacceleration transmissibility under various applied currents. The experimental results indicate that the resonance fre-quency of the integrated system can be tuned from 10 to 20 Hz, and the transmissibility peak value reduces 20.67%simultaneously, for which the proposed bearing can be used for seismic mitigation. Finally, the stiffness and damping ofthe laminated magnetorheological elastomer bearing integrated vibration mitigation system are identified by theresponse characteristics.
KeywordsMagnetorheological elastomers, vibration mitigation, resonance frequency shift, parameter identification
Introduction
The widespread construction of railroad and highwaybridges has drawn an increased attention in seismic isola-tion bearings as supports of the bridges. As a result ofemploying the seismic isolation bearings, the superstruc-tures’ motion is decoupled from the bridge piers’ motionduring external excitations (such as earthquakes), thusreducing the transmitted acceleration by energy dissipa-tion in the isolator, as shown in Figure 1(a). Nevertheless,conventional laminated rubber bearings are unable toalter their performance due to the passive nature of tradi-tional rubber (Tyleri, 1991). As one of the most potentialalternative solution, the ‘‘smart’’ semi-active vibration iso-lators with adjustable damping and stiffness are intendedto mitigate the destructive vibration (Nagarajaiah andSahasrabudhe, 2006; Ramallo et al., 2002; Yi et al., 2001;Yoshioka et al., 2002). In addition, variable damping andstiffness isolators, as shown in Figure 1(b), are able toachieve shift in resonance frequency and attenuation intransmissibility peak value by changing the properties ofthe isolation system (Behrooz et al., 2011; Dyke et al.,1996).
Magnetorheological elastomers (MREs) mainly con-sist of micro-sized magnetic ferromagnetic particles
dispersed in a polymer matrix (Gong et al., 2005; Jollyet al., 1996). MREs belong to a semi-active smart mate-rial that could vary its rheological, mechanical, andmagnetic properties continuously, rapidly, and reversi-bly under an applied magnetic field (Ginder et al., 1999;Shen et al., 2004; Zhou, 2003). Owing to the field-dependent damping and stiffness, the MREs have anadvantage in developing the semi-active controllablebase isolators (Li et al., 2013a; Yang et al., 2015).Recently, several attempts have been made to developMRE-based semi-active isolation systems for anti-seismic structures (Koo et al., 2009). Eem et al. (2011)investigated the feasibility of MRE-based isolation sys-tem by numerical evaluation, while Jung et al. (2011)corroborated that the smart base-isolation system out-performs the passive-type base-isolation system through
Key Laboratory of Opto-electronic Technology and Systems, Ministry of
Education of China, College of Optoelectronic Engineering, Chongqing
University, Chongqing, China
Corresponding author:
Miao Yu, Key Laboratory of Opto-electronic Technology and Systems,
Ministry of Education of China, College of Optoelectronic Engineering,
small-scale experiment. Behrooz et al. (2013) presenteda variable stiffness and damping isolator (VSDI) in ascaled building system, and the experimental resultsshowed the VSDI could reduce the acceleration andrelative displacement of the ground. Li et al. (2013b)developed an adaptive seismic isolator and evaluatedthe properties of damping force and energy dissipation.The laminated structure of the smart isolator featuringMRE material originates from conventional seismic rub-ber bearing, which has been adopted in engineering appli-cation. However, the distribution of the magnetic fieldinside and the properties of frequency shift in laminatedMRE-based isolation system have not been studied yet.The primary motivation for perfecting the prior works isto consummate electromagnetic simulation in the mag-netic circuit design process, as well as evaluate the field-dependent adjustable natural frequency of the vibrationmitigation system through experimental research.
This study was structured as follows: first, the MREsused for laminated structure were fabricated, and thenthe laminated MRE bearing was proposed, while anelectromagnetic simulation was conducted. Second, asine sweeping-frequency vibration testing was carriedout to verify the performance of proposed laminatedMRE bearing, and then the stiffness and damping ofintegrated vibration system were identified using theexperimental results. The conclusions are summarizedat the end.
Design of laminated MRE bearingprototype
Referring to the conventional laminated or multi-layered structure of rubber bearing, a novel controllable
semi-active anti-seismic bearing prototype utilizing pre-pared MREs is presented, and then the correspondingelectromagnetic field is simulated and analyzed.
Preparation of MREs
In this work, the ingredients of the MREs are as fol-lows: two-component room temperature vulcanizing(RTV) silicone rubber (type: SC-2110; Beijing SanchenIndustrial New Material Co. Ltd, China), silicone oil,and carbonyl iron particles (type: JCF2-2; Jilin JienNickel Industry Co. Ltd, China). The iron particlesphere diameter is between 5 and 8 mm. The mass frac-tion of the iron particles, silicone rubber, and siliconeoil was 70%, 20%, and 10%, respectively. To produceMREs, all ingredients were mixed in a beaker and thenstirred for approximately 10 min at room temperature,and then the resulting mixture was placed in aluminummolds after removing air bubbles. Finally, after curingfor 24 h at room temperature, all MRE specimens withthe dimension of 60 mm in diameter and 2 mm in thick-ness were trimmed from aluminum molds and are readyfor use.
Description of mechanical configurations
As illustrated in Figure 2, the proposed bearing consistsof laminated MREs with steel plates, solenoid electro-magnetic coil, sliding surface, steel sleeve, and mount-ing plate. The laminated structure, which isconventionally used in the seismic rubber bearing, ismostly effective to withstand large vertical loads whileprocessing controllable lateral stiffness to achievehigher displacement in the horizontal direction by
Figure 1. Representation of an isolated bridge superstructure: (a) schematic diagram and (b) dynamical model.
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applying the external magnetic field. In this design, 20layers of MREs with 2 mm thickness and 19 layers ofelectrical pure iron with 1 mm thickness are curedtogether utilizing silicone rubber. In order to generatesufficient magnetic field, the coil is winded on a thinaluminum bobbin, in which the diameter of the cop-per wire is 0.8 mm and the total electric resistance of1400 turns is 17.2 O. Moreover, the interval betweenthe laminated structure and the inner wall of the coilcylinder is set to 10 mm, which indicates the maxi-mum lateral displacement. To enable the motion ofthe proposed bearing, a small gap of 2 mm betweenthe sliding surface and steel sleeve is reserved, inwhich 24 uniform distributed magnetic steel balls with3.25 mm diameter are employed to enhance the carry-ing capacity and horizontal stability of the prototype.Eventually, other dimensions of parts meet therequirements of assembly design, as listed in Table 1.
Electromagnetic analysis
It is well-known that the electromagnetic simulationand optimization are significant parts in developingmagnetorheological (MR) devices. In particular, mag-netic properties and mechanical dimensions of thevarious components installed in MR devices are thecore parameters for magnetic circuit design. In thisstudy, the nonlinear magnetic permeability of theselected MREs is taken fully into account. The mag-netic properties of MREs were evaluated using thevibrating sample magnetometer (VSM), as shown inFigure 3.
Subsequently, the electromagnetic analysis is per-formed by Ansoft Maxwell. The results of the magneticflux density and its path at the maximum applied cur-rent of 5 A are presented in Figure 4. It is observed thatthe magnetic field intensity reveals a homogeneous dis-tribution of about 450 mT in the laminated MRE struc-ture in Figure 4(a). In Figure 4(b), the magnetic fluxlines go through the laminated MREs with steel platesplaced perpendicularly, which guarantees the effective-ness of MREs under the shear mode operation. The
amount of magnetic flux density inside the MRE lami-nated structure at different location is shown in Figure5. In the illustration, the magnetic flux density insidethe activation area of the MRE bearing increases withincreasing applied currents. Also, there is little differ-ence of magnetic flux density among different locationsof laminated MRE structure.
Experimental study of the prototype
In this section, both experimental studies and systemparameter identification have been conducted to ver-ify the feasibility of employing the proposed lami-nated MRE bearing for seismic mitigation control.Experimentally, the sine sweeping-frequency vibra-tion method is adopted to evaluate the transmissibil-ity effect, generally known as the ratio of the responseacceleration to the base exciting acceleration, of themanufactured prototype. Theoretically, the kineticequation of the experimental system and the equationof acceleration transmissibility are brought to identifythe stiffness and damping of the integrated system.
Experimental setup
Figure 6 shows the principal experimental setup for abase-isolated system featuring the proposed laminatedMRE bearing. All tests were conducted using electro-dynamics vibration shaker (type: DC-1000-15; SuzhouSushi Testing Instrument Co., Ltd), to which a hori-zontal sliding table (type: SV-0505; Suzhou SushiTesting Instrument Co., Ltd) was joined together. Themounting plate of laminated MRE bearing prototypewas mounted on the horizontal sliding table, while thetop cap could motion in the horizontal direction with-out constraints. Two accelerators (model: 333B52; PCBPiezotronics, Inc.) were utilized in the experiment tomeasure the acceleration of base exciting vibration andtop cap response vibration, respectively. The signals oftwo accelerators were transferred to a data acquisitioninstrument for processing and analyzing via a three-channel signal conditioner (model: 480B21; PCBPiezotronics, Inc.).
For all tests, a frequency sweeping sinusoidal excita-tion within a range from 5 to 45 Hz at a constant accel-eration of 0.05 g with varying applied currents wasused. The currents to the winding coil were indepen-dently altered from 0 to 5 A with 1 A increment, whichwere energized by a direct current (DC) power supplywith a capacity of 120 V and 10 A.
Experimental results and discussion
Using the time-domain acceleration data, the transferfunction is estimated and calculated through MATLABprogramming. Figure 7 displays the acceleration trans-missibility results for a frequency range of 5–45 Hz with
Table 1. Primary mechanical dimensions of the laminated MREbearing.
Parts Dimension (mm)
Diameter of MREs/steel plates 60Height of laminated MREs with steel plates 59Distance between laminated structureand coil frame
10
Gap between sliding surface and steel sleeve 2Diameter of sliding surface 182Diameter of mounting plate 204Height of whole apparatus 92
MREs: magnetorheological elastomers.
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different applied currents to the proposed laminatedMRE bearing. As is seen, in the off-state (zero appliedcurrent), the resonance frequency of the integratedvibration isolation system is situated at approximately10 Hz, while in the on-state (5 A applied current), theresonance frequency moves to approximately 20 Hzwith a transmissibility peak value of 5.87. It is obviousthat when the current is applied, the resonance fre-quency apparently shift to the higher frequency, asshown in the top-right corner of Figure 7. This indicatesthat the laminated MRE bearing has the capacity toalter the stiffness to a large extent. Furthermore, theintegrated system damping properties play an impor-tant role in attenuating response amplitude at the reso-nance frequency. This is evidenced by that themaximum transmissibility peak value is about 7.40 anddecreases with increasing applied current to a peakvalue of 5.87 at the maximum current of 5 A, a reduc-tion of 20.67%.
Additional result of the acceleration transmissibilityindicates that the intersection of off-state and on-state,approximately 13.4 Hz in Figure 8, can be regarded asthe switch frequency for on–off control of vibrationmitigation. It means that when the excitation frequencyis lower than the switch frequency, the applied controlcurrent can be set at the maximum value, 5 A, andreversely when the excitation frequency is larger thanthe switch frequency, the applied control current canbe switched to 0 A, namely, power off.
Parameter identification of vibrationmitigation system
The experimental integrated system utilizing proposedprototype can be considered as a single-degree-of-free-dom (SDOF) system, which consists of a constant massand a viscoelastic device. Figure 9 shows the equivalentmechanical model of integrated vibration mitigationsystem, which is simplified for the experimental systemin Figure 6. The equation of motion subjected to a basemotion is given as
m€xm(t)+C _xm(t)� _xg(t)� �
+K xm(t)� xg(t)� �
= 0 ð1Þ
where m is the total weight of the top cap including thetop steel plate; €xg and €xm are the ground exciting accel-eration and top cap response acceleration, respectively;C and K are the changeable field-controlled dampingand stiffness, respectively.
To identify parameters of the integrated base-isolated system with variable stiffness and damping, thefollowing equations are employed to calculate theacceleration transmissibility characteristics (De Silva,2006)
Figure 5. Results of electromagnetic analysis inside the MRE plates at different locations.MRE: magnetorheological elastomer.
Figure 6. Photograph of the main experimental setup forlaminated MRE bearing integrated system.MRE: magnetorheological elastomer.
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where g = f =fpeak and z =C=2ffiffiffiffiffiffiffimKp
. In the above equa-tions, g is the normalized frequency, which is equal tothe ratio between input exciting frequency f and peakfrequency (or resonance frequency) fpeak , and z is thedamping ratio of integrated system. In the experiments,the payload mass m is 2 kg, and the maximum Tr is cho-sen from Figure 7, so g = 1. According to equations (2)and (3), the stiffness and damping of integrated systemin response to the base excitations with 0.05 g
Figure 8. Optimized frequency response curve of the integrated system.
Figure 7. Transmissibility of 0.05 g amplitude acceleration input for different currents.
Figure 9. Equivalent mechanical model of the integratedvibration mitigation system.
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amplitude sinusoidal acceleration can be obtained,which are listed in Table 2.
Obviously, from the results of integrated systemparameter identification, the increase in stiffness anddamping is up to 312.67% and 157.49%, respectively,with the increasing magnetic field strength, energizedby the input currents varying from 0 to 5 A. As such,the attenuation of acceleration transmissibility and theshift of resonance frequency can be achieved by the pro-posed laminated MRE bearing for seismic mitigation.
Conclusion
In this work, a modified laminated MRE bearing pro-totype featuring conventional laminated structure inthe seismic rubber bearing was developed and manu-factured. The electromagnetic simulation of the pro-posed bearing revealed the distribution of magneticfield in the device and the effectiveness of magnetic cir-cuit design. According to the experiment of SDOF inte-grated vibration system, the stiffness and dampingcould be changed up to 312.67% and 157.49% under 5A input current, respectively. This was the reason forthe shift of resonance frequency and the attenuation oftransmissibility peak value under various applying cur-rents. The above results demonstrated the performanceof the proposed laminated MRE bearing and its possi-bility of seismic vibration mitigation by frequency shift-ing under different magnetic fields.
Declaration of conflicting interests
The authors declared no potential conflicts of interest withrespect to the research, authorship, and/or publication of thisarticle.
Funding
This work was financially supported by the National NaturalScience Foundation of China (Grant No. 61203098), theNational Sci-Tech Support Plan (2012BAF06B00F), and theFundamental Research Funds for the Central Universities(Grant Nos CDJZR13120090 and CDJZR120018). Theauthors are grateful for their supports.
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