• Structural Engineering and Mechanics
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• v.48 no.4
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• pp.479-500
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• 2013

This paper presents the experimental as well as analytical study conducted on layer-bonded scrap tire rubber pad (STRP) isolators to develop low-cost seismic isolators applicable to structures in developing countries. The STRP specimen samples were produced by stacking the STRP layers one on top of another with the application of adhesive. In unbonded application, the STRP bearings were placed between the substructure and superstructure without fastening between the contact surfaces which allows roll-off of the contact supports. The vertical compression and horizontal shear tests were conducted with varying axial loads. These results were used to compute the different mechanical properties of the STRP isolators including vertical stiffness, horizontal effective stiffness, average horizontal stiffness and effective damping ratios. The load-displacement relationships of STRP isolators obtained by experimental and finite element analysis results were found to be in close agreement. The tested STRP samples show energy dissipation capacity considerably greater than the natural rubber bearings. The layer-bonded STRP isolators serve positive incremental force resisting capacity up to the shear strain level of 150%.

• Structural Engineering and Mechanics
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• v.61 no.1
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• pp.31-47
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• 2017

As a relatively new type of multi-layered rubber-based seismic isolators, fiber-reinforced elastomeric isolators (FREIs) are composed of several thin rubber layers reinforced with flexible fiber sheets. Limited analytical studies in literature have pointed out that "warping" (distortion) of reinforcing sheets has significant influence on buckling behavior of FREIs. However, none of these studies, to the best knowledge of authors, has investigated their warping behavior, thoroughly. This study aims to investigate, in detail, the warping behavior of strip-shaped FREIs by deriving advanced analytical solutions without utilizing the commonly used "pressure", incompressibility, inextensibility and the "linear axial displacement variation through the thickness" assumptions. Studies show that the warping behavior of FREIs mainly depends on the (i) aspect ratio (shape factor) of the interior elastomer layers, (ii) Poisson's ratio of the elastomer and (iii) extensibility of the fiber sheets. The basic assumptions of the "pressure" method as well as the commonly used incompressibility assumption are valid only for isolators with relatively large shape factors, strictly incompressible elastomeric material and nearly inextensible fiber reinforcement.

• Computers and Concrete
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• v.16 no.4
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• pp.503-529
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• 2015

Traditionally, multi-story buildings are designed to provide stiffer structural support to withstand lateral earthquake loading. Introducing flexible elements at the base of a structure and providing sufficient damping is an alternative way to mitigate seismic hazards. These features can be achieved with a device known as an isolator. This paper covers the design of base isolators for multi-story buildings in medium-risk seismicity regions and evaluates the structural responses of such isolators. The well-known tower building for police personnel built in Dhaka, Bangladesh by the Public Works Department (PWD) has been used as a case study to justify the viability of incorporating base isolators. The objective of this research was to establish a simplified model of the building that can be effectively used for dynamic analysis, to evaluate the structural status, and to suggest an alternative option to handle the lateral seismic load. A finite element model was incorporated to understand the structural responses. Rubber-steel bearing (RSB) isolators such as Lead rubber bearing (LRB) and high damping rubber bearing (HDRB) were used in the model to insert an isolator link element in the structural base. The nonlinearities of rubber-steel bearings were considered in detail. Linear static, linear dynamic, and nonlinear dynamic analyses were performed for both fixed-based (FB) and base isolated (BI) buildings considering the earthquake accelerograms, histories, and response spectra of the geological sites. Both the time-domain and frequency-domain approaches were used for dynamic solutions. The results indicated that for existing multi-story buildings, RSB diminishes the muscular amount of structural response compared to conventional non-isolated structures. The device also allows for higher horizontal displacement and greater structural flexibility. The suggested isolation technique is able to mitigate the structural hazard under even strong earthquake vulnerability.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.1071-1084
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• 2022

The present study aims to investigate the dynamic properties of a novel isolation system composed of separate rubber and wire isolators. The testing program comprised pure compressive, pure-shear, compressive-stress dependence, and shear-strain dependence tests that used full-scale test specimens according to ISO 22762-1. A total of 22 test specimens were fabricated and investigated. Among the tests, the pure compressive test was a destructive test that reached up to the failure stage, whereas the others were nondestructive tests before the failure stage. Similar to the pure-shear test, at each compressive-stress level in the compressive dependence test or at each shear-strain level in the shear-strain dependence test, the cyclic loading was conducted for three cycles. In the nondestructive tests, examination of the dynamic shear properties in the X-direction was independent of the Y-direction. The test results revealed that the increase in the shear strain increased the energy dissipation but decreased the damping ratio, whereas the increase in the compressive stress increased the damping ratio. In addition, a macro model was developed to simulate the load-displacement response of the isolation systems, and the prediction results were consistent with the experimental results.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.5
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• pp.385-392
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• 2014

The isolators have been generally used to reduce a seismic force. If the isolators apply to the nuclear power plants(NPPs), the durability and capacity for the structures and equipments should be ensured during the life time. In this study, the long-term behavior of isolated NPPs was analyzed for ensuring the seismic safety. The properties of isolator due to the age-related degradation were analyzed. And the seismic behavior of isolated buildings was analyzed by considering the aging of rubber bearings in different temperature environments. According to the analysis results, the natural frequency of structures was increased with time. But the maximum acceleration and maximum displacement of isolated structures have not changed significantly. Although the damaged of structure did not occurred by aging of isolators, it was presented that the spectral acceleration at the target frequency of isolated structure increased with the temperature. Therefore the isolators in the isolated buildings should be carefully designed and manufactured considering the temperature-dependancy of rubber material.

• Elastomers and Composites
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• v.37 no.3
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• pp.183-191
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• 2002

Rubber materials with excellent damping property are widely applied for vibration isolators. The dynamic characteristics of the rubber materials for vibration isolators were investigated. Dynamic tests for rubber materials with five different hardness were performed. In dynamic tests for test specimen, non-resonance method was used to obtain the dynamic storage modulus and loss factor. Moreover, the effect of dynamic vibration frequency, strain amplitude and temperature were investigated. As results, the storage modulus and loss factor generally increase when the hardness and frequency increase, and the glass transition temperature is $-50^{\circ}C$ by a large change in modulus and loss factor.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.2
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• pp.221-230
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• 2004

In this paper, the dynamic response of a multi-story steel moment resisting frame equipped with viscoelastic dampers or lead rubber bearing type isolators subjected to seismic loads is investigated analytically. The objective of this study is to find the best location of viscoelastic dampers by the maximum stress method and maximum story drifts method from structure analysis. Also, a secondary objective of the study is to compare the member force, combined stress, and natural period of the structure retrofitted with viscoelastic dampers or lead rubber bearing type isolators to find effective vibration control method.

• Journal of KSNVE
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• v.7 no.5
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• pp.789-796
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• 1997

In this study a conventional rubber mount and a new form of base isolator made of steel spring coated with natural and articial rubber were manufactured and tested on a shaking table to investigate the capacity of reducing the vertical vibration of a building induced by subway train. The model structure used in the test is a 1/4 scaled steel structure, and a white noise input and train vibration records were used to check the effectiveness of the isolators. According to the results all three types of isolators turned out to perform effectively in reducing the acceleration and the natural rubber-coated one is ranked best among the isolators. However the vertical displacement of the model is increased due to the instolation of the bearings, and the safty against the lateral load induced by earthquake ground motion should be provided to be able to apply the system to the real buildings.

• Nuclear Engineering and Technology
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• v.46 no.5
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• pp.605-618
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• 2014

The effects of variability of the mechanical properties of lead rubber bearings on the response of a seismic isolation system are investigated. Material variability in manufacturing, aging, and operation temperature is assumed, and two variation models of an isolation system are considered. To evaluate the effect of ground motion characteristics on the response, 27 earthquake record sets with different peak A/V ratios were selected, and three components of ground motions were used for a seismic response analysis. The response in an isolation system and a superstructure increases significantly for ground motions with low A/V ratios. The variation in the mechanical properties of isolators results in a significant influence on the shear strains of the isolators and the acceleration response of the superstructure. The variation provisions in the ASCE-4 are reasonable, but more strict variation limits should be given to isolation systems subjected to ground motions having low A/V ratios. For application of seismic isolation systems to safety-related nuclear structures, the variation in the material and mechanical properties of the isolation system should be properly controlled during the manufacturing and aging processes. In addition, special consideration should be given to minimize the accidental torsion caused by the dissimilarity in the stiffness variations of the isolators.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.2
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• pp.39-48
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• 1997

New form of base isolators made of steel spring coated with both natural and artficial rubber were manufactured and tested for material properties. Shaking table experiments were performed using a model structure attached with the bearings. The model structure used in the test is a 1/4 scaled steel structure, and earthquake records were used to check the lateral and vertical stability and effectiveness of the isolators. According to the results all three types of isolators turned out to be effective in reducing the acceleration induced by the earthquake vibration.