• Title/Summary/Keyword: lead-rubber bearings

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System-Level Seismic Fragility Evaluation of Bridge Considering Aging Effects (노후도를 고려한 교량의 시스템-수준 지진취약도 평가)

  • Kong, Sina;Moon, Jiho;Song, Jong-Keol
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.35 no.3
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    • pp.149-158
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    • 2022
  • As a bridge ages, its mechanical properties and structural performance deteriorate, degrading its seismic performance during a strong earthquake. In this study, the aging of piers and bridge bearings was quantified in several stages and reflected in the analysis model, enabling the evaluation of the member-level seismic fragility of these bearings. Moreover, by assuming that the failure mechanism of a bridge system is a series system, a method for evaluating the system-level seismic fragility based on the member-level seismic fragility analysis result is formulated and proposed. For piers with rubber and lead-rubber bearings (members vulnerable to aging effects), five quantitative degrees of aging (0, 5, 10, 25, and 40%) are assumed to evaluate the member-level seismic fragility. Then, based on the result, the system-level seismic fragility evaluation was implemented. The pier rather than the bridge bearing is observed to have a dominant effect on the system-level seismic fragility. This means that the seismic fragility of more vulnerable structural members has a dominant influence on the seismic fragility of the entire bridge system.

Seismic response variation of multistory base-isolated buildings applying lead rubber bearings

  • Islam, A.B.M. Saiful;Al-Kutti, Walid A.
    • Computers and Concrete
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    • v.21 no.5
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    • pp.495-504
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    • 2018
  • The possibility of earthquakes in vulnerable regions indicates that efficient technique is required for seismic protection of buildings. During the recent decades, the concept is moving towards the insertion of base isolation on seismic prone buildings. So, investigation of structural behavior is a burning topic for buildings to be isolated in base level by bearing device. This study deals with the incorporation of base isolation system and focuses the changes of structural responses for different types of Lead Rubber Bearing (LRB) isolators. A number of sixteen model buildings have been simulated selecting twelve types of bearing systems as well as conventional fixed-base (FB) scheme. The superstructures of the high-rise buildings are represented by finite element assemblage adopting multi-degree of freedoms. Static and dynamic analyses are carried out for FB and base isolated (BI) buildings. The dynamic analysis in finite element package has been performed by the nonlinear time history analysis (THA) based on the site-specific seismic excitation and compared employing eminent earthquakes. The influence of the model type and the alteration in superstructure behavior of the isolated buildings have been duly assessed. The results of the 3D multistory structures show that the lateral forces, displacement, inertia and story accelerations of the superstructure of the seismic prone buildings are significantly reduced due to bearing insertion. The nonlinear dynamic analysis shows 12 to 40% lessening in base shear when LRB is incorporated leading to substantial allowance of horizontal displacement. It is revealed that the LRB isolators might be potential options to diminish the respective floor accelerations, inertia, displacements and base shear whatever the condition coincides. The isolators with lower force intercept but higher isolation period is found to be better for decreasing base shear, floor acceleration and inertia force leading to reduction of structural and non-structural damage. However, LRB with lower isolator period seems to be more effective in dropping displacement at bearing interface aimed at reducing horizontal shift of building structure.

Generic optimization, energy analysis, and seismic response study for MSCSS with rubber bearings

  • Fan, Buqiao;Zhang, Xun'an;Abdulhadi, Mustapha;Wang, Zhihao
    • Earthquakes and Structures
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    • v.19 no.5
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    • pp.347-359
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    • 2020
  • The Mega-Sub Controlled Structure System (MSCSS), an innovative vibration passive control system for building structures, is improved by adding lead rubber bearings (LRBs) on top of the substructure. For the new system, a genetic algorithm is used to optimize the dynamic parameters and distributions of dampers and LRBs. The program uses various seismic performance indicators as optimization objectives, and corresponding results are compared. It is found that the optimization procedure for maximizing the energy dissipation ratio yields the best solutions, and optimized models have consistent seismic performances under different earthquakes. Seismic performances of optimized MSCSS models with and without LRBs, as well as the traditional Mega-Sub Structure model, are evaluated and compared under El Centro wave, Taft wave and 20 other artificial waves. In both elastic and plastic analysis, the model with LRBs shows significantly smaller story drift and horizontal acceleration than those of the other two models, and fewer plastic hinges are developed during severe earthquakes. Energy analysis also shows that LRBs installed in proper locations increase the deformation and energy dissipation of dampers, thereby significantly reduce the kinetic, potential, and hysteretic energy in the structure. However, LRBs do not have to be mounted on all the additional columns. It is also demonstrated that LRBs at unfavorable locations can decrease the energy dissipation for dampers. After LRBs are installed, the optimal damping coefficient and the optimal damping exponent of dampers are reduced to produce the best damping effect.

Comparative Seismic Design of Bridges with Lead Rubber and Steel Bearings for the Ductile Failure Mechanism (지진격리교량과 강재받침교량의 연성파괴메커니즘에 의한 비교내진설계)

  • Kook, Seung Kyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.1A
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    • pp.173-181
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    • 2006
  • Many isolated bridges are designed and constructed after the introduction of the seismic design. However those bridges designed in engineering fields have unnecessarily high serviceability limit and brittle failure mechanism, which do not satisfy the seismic design concept. Such design results are due to the excessive substructure stiffness of the conventional design method as well as the misunderstanding of the seismic design method. In this study an isolated bridge designed with the conventional design method is selected and the same bridge with steel bearings is modelled for the comparative seismic design. From the comparison, the seismic design procedures satisfying the required performance levels are provided for the two bridges. It is confirmed that the isolated bridge requires more complicated design procedure with trial and error methods and reanalyses but provides higher serviceability limit compared to the bridge with steel bearings. However, because the required serviceability limit can also be obtained by adjusting substructure stiffness, it is a resonable seismic design process that an isolated bridge is to be considered as an alternative design when the ductile failure mechanism is not obtained with a bridge with steel bearings.

Experimental Study on the Temperature Dependency of Full Scale Low Hardness Lead Rubber Bearing (Full-scale 저경도 납면진받침의 온도의존성에 대한 실험적 연구)

  • Park, Jin Young;Jang, Kwang-Seok;Lee, Hong-Pyo;Lee, Young Hak;Kim, Heecheul
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.25 no.6
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    • pp.533-540
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    • 2012
  • Rubber laminated bearings with lead core are highly affected by changes in temperature because key materials which are rubber and lead have temperature dependencies. In this study, two full scale LRB(D800, S=5) are manufactured and temperature dependency tests on shear properties are accomplished. The shear properties at the 3rd cycle are used at $-10^{\circ}C$, $0^{\circ}C$, $10^{\circ}C$, $20^{\circ}C$, $30^{\circ}C$, $40^{\circ}C$ respectively. The double shear configuration, simultaneously testing two pieces, is applied for compression shear test in order to minimize the friction effects due to the test machine, described in ISO 22762-1:2010. Characteristic strength, post-yield stiffness, effective stiffness, equivalent damping ratio are estimated and presented coefficient due to the temperature changes.

Incorporation preference for rubber-steel bearing isolation in retrofitting existing multi storied building

  • Islam, A.B.M. Saiful;Jumaat, Mohd Zamin;Hussain, Raja Rizwan;Hosen, Md. Akter;Huda, Md. Nazmul
    • 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.

Seismic Behavior and Estimation for Base Isolator Bearings with Self-centering and Reinforcing Systems (자동복원 및 보강 시스템과 결합된 면진받침의 지진거동과 평가)

  • Hu, Jong Wan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.35 no.5
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    • pp.1025-1037
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    • 2015
  • Flexible base isolation bearings that separate superstructure from ground have been widely used in the construction field because they make a significant contribution to increasing the fundamental period of the structure, thereby decreasing response acceleration transmitted into the superstructure. However, the established bearing devices installed to uphold the whole building give rise to some problems involved with failure and collapse due to lack of the capacity as modern structures are getting more massive and higher. Therefore, this study suggests new isolation bearings assembled with additional restrainers enabled to reinforcing and recentering, and then evaluates their performance to withstand the seismic load. The superelastic shape memory alloy (SMA) bars are installed into the conventional lead-rubber bearing (LRB) devices in order to provide recentering forces. These new systems are modeled as component spring models for the purpose of conducting nonlinear dynamic analyses with near fault ground motion data. The LRB devices with steel bars are also designed and analyzed to compare their responses with those of new systems. After numerical analyses, ultimate strength, maximum displacement, permanent deformation, and recentering ratio are compared to each model with an aim to investigate which base isolation models are superior. It can be shown that LRB models with superelastic SMA bars are superior to other models compared to each other in terms of seismic resistance and recentering effect.

Estimation of the Isolator Displacement for the Performance Based Design of Nuclear Power Plants (원전 적용을 위한 면진장치의 성능기반 설계 변위 추정)

  • Kim, Jung Han;Choi, In-Kil;Kim, Min Kyu
    • Journal of the Earthquake Engineering Society of Korea
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    • v.18 no.6
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    • pp.291-299
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    • 2014
  • There has been an increasing demand for introducing a base isolation system to secure the seismic safety of a nuclear power plant. However, the design criteria and the safety assessment methodology of a base isolated nuclear facility are still being developed. A performance based design concept for the base isolation system needs to be added to the general seismic design procedures. For the base isolation system, the displacement responses of isolators excited by the extended design basis earthquake are important as well as the design displacement. The possible displacement response by the extended design basis earthquake should be limited less than the failure displacement of the isolator. The failure of isolators were investigated by an experimental test to define the ultimate strain level of rubber bearings. The uncertainty analysis, considering the variations of the mechanical properties of isolators and input ground motions, was performed to estimate the probabilistic distribution of the isolator displacement. The relationship of the displacement response by each ground motion level was compared in view of a period elongation and a reduction of damping. Finally, several examples of isolator parameters are calculated and the considerations for an acceptable isolation design is discussed.

Displacement-based design approach for highway bridges with SMA isolators

  • Liu, Jin-Long;Zhu, Songye;Xu, You-Lin;Zhang, Yunfeng
    • Smart Structures and Systems
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    • v.8 no.2
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    • pp.173-190
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    • 2011
  • As a practical and effective seismic resisting technology, the base isolation system has seen extensive applications in buildings and bridges. However, a few problems associated with conventional lead-rubber bearings have been identified after historical strong earthquakes, e.g., excessive permanent deformations of bearings and potential unseating of bridge decks. Recently the applications of shape memory alloys (SMA) have received growing interest in the area of seismic response mitigation. As a result, a variety of SMA-based base isolators have been developed. These novel isolators often lead to minimal permanent deformations due to the self-centering feature of SMA materials. However, a rational design approach is still missing because of the fact that conventional design method cannot be directly applied to these novel devices. In light of this limitation, a displacement-based design approach for highway bridges with SMA isolators is proposed in this paper. Nonlinear response spectra, derived from typical hysteretic models for SMA, are employed in the design procedure. SMA isolators and bridge piers are designed according to the prescribed performance objectives. A prototype reinforced concrete (RC) highway bridge is designed using the proposed design approach. Nonlinear dynamic analyses for different seismic intensity levels are carried out using a computer program called "OpenSees". The efficacy of the displacement-based design approach is validated by numerical simulations. Results indicate that a properly designed RC highway bridge with novel SMA isolators may achieve minor damage and minimal residual deformations under frequent and rare earthquakes. Nonlinear static analysis is also carried out to investigate the failure mechanism and the self-centering ability of the designed highway bridge.

Comparison of Seismic Retrofit Efficiencies of Base Isolation Systems for Existing Bridges

  • 조효남;엄원석
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.10a
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    • pp.81-86
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    • 2000
  • In recent modern protective systems have been introduced to reduce the vulnerability of bridges to seismic events. These protective systems include base isolation devices of different types, damping devices and active control devices. The objective of this study is to analytically evaluate the efficiency of a seismic retrofit scheme using base isolation systems, such as lead rubber bearings and sliding isolators. In this study, a triaxial model was used, which is capable of accurately developing the behavior of sliding isolators including the influence of the changing vertical force and velocity on the friction coefficients. Seismic response analyses of the bridge before and after retrofit were carried out by using a three-dimensional nonlinear seismic analysis program, IDARC-BRIDGE. To evaluate the efficiency of a retrofit scheme using triaxial isolators, a comparative study of performances of above two base isolation systems was conducted, and the numerical results show that the triaxial isolation solution can effectively reduce the sheat forces at the piers for the vertical ground motion.

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