DOI: 10.1177/1045389X15577654 seismic mitigation of ... dependent damping and stiffness, the MREs have

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  • Special Issue Article

    Journal of Intelligent Material Systems and Structures 2015, Vol. 26(14) 1818–1825 � 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: yumiao@cqu.edu.cn

    at Chongqing University on November 23, 2015jim.sagepub.comDownloaded from

    http://jim.sagepub.com/

  • small-scale experiment. Behrooz et al. (2013) presented a variable stiffness and damping isolator (VSDI) in a scaled building system, and the experimental results showed the VSDI could reduce the acceleration and relative displacement of the ground. Li et al. (2013b) developed an adaptive seismic isolator and evaluated the properties of damping force and energy dissipation. The laminated structure of the smart isolator featuring MRE material originates from conventional seismic rub- ber bearing, which has been adopted in engineering appli- cation. However, the distribution of the magnetic field inside and the properties of frequency shift in laminated MRE-based isolation system have not been studied yet. The primary motivation for perfecting the prior works is to consummate electromagnetic simulation in the mag- netic circuit design process, as well as evaluate the field- dependent adjustable natural frequency of the vibration mitigation system through experimental research.

    This study was structured as follows: first, the MREs used for laminated structure were fabricated, and then the laminated MRE bearing was proposed, while an electromagnetic simulation was conducted. Second, a sine sweeping-frequency vibration testing was carried out to verify the performance of proposed laminated MRE bearing, and then the stiffness and damping of integrated vibration system were identified using the experimental results. The conclusions are summarized at the end.

    Design of laminated MRE bearing prototype

    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 corresponding electromagnetic 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 Sanchen Industrial New Material Co. Ltd, China), silicone oil, and carbonyl iron particles (type: JCF2-2; Jilin Jien Nickel Industry Co. Ltd, China). The iron particle sphere diameter is between 5 and 8 mm. The mass frac- tion of the iron particles, silicone rubber, and silicone oil was 70%, 20%, and 10%, respectively. To produce MREs, all ingredients were mixed in a beaker and then stirred for approximately 10 min at room temperature, and then the resulting mixture was placed in aluminum molds after removing air bubbles. Finally, after curing for 24 h at room temperature, all MRE specimens with the dimension of 60 mm in diameter and 2 mm in thick- ness were trimmed from aluminum molds and are ready for use.

    Description of mechanical configurations

    As illustrated in Figure 2, the proposed bearing consists of laminated MREs with steel plates, solenoid electro- magnetic coil, sliding surface, steel sleeve, and mount- ing plate. The laminated structure, which is conventionally used in the seismic rubber bearing, is mostly effective to withstand large vertical loads while processing controllable lateral stiffness to achieve higher displacement in the horizontal direction by

    Figure 1. Representation of an isolated bridge superstructure: (a) schematic diagram and (b) dynamical model.

    Xing et al. 1819

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  • applying the external magnetic field. In this design, 20 layers of MREs with 2 mm thickness and 19 layers of electrical pure iron with 1 mm thickness are cured together utilizing silicone rubber. In order to generate sufficient magnetic field, the coil is winded on a thin aluminum bobbin, in which the diameter of the cop- per wire is 0.8 mm and the total electric resistance of 1400 turns is 17.2 O. Moreover, the interval between the laminated structure and the inner wall of the coil cylinder is set to 10 mm, which indicates the maxi- mum lateral displacement. To enable the motion of the proposed bearing, a small gap of 2 mm between the sliding surface and steel sleeve is reserved, in which 24 uniform distributed magnetic steel balls with 3.25 mm diameter are employed to enhance the carry- ing capacity and horizontal stability of the prototype. Eventually, other dimensions of parts meet the requirements of assembly design, as listed in Table 1.

    Electromagnetic analysis

    It is well-known that the electromagnetic simulation and optimization are significant parts in developing magnetorheological (MR) devices. In particular, mag- netic properties and mechanical dimensions of the various components installed in MR devices are the core parameters for magnetic circuit design. In this study, the nonlinear magnetic permeability of the selected MREs is taken fully into account. The mag- netic properties of MREs were evaluated using the vibrating sample magnetometer (VSM), as shown in Figure 3.

    Subsequently, the electromagnetic analysis is per- formed by Ansoft Maxwell. The results of the magnetic flux density and its path at the maximum applied cur- rent of 5 A are presented in Figure 4. It is observed that the 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 flux lines go through the laminated MREs with steel plates placed 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 diffe