Elastomeric Isolation Bearings Research Articles

Seismic performance of reinforced concrete bridge using friction pendulum bearing under different friction coefficients

Application of seismic isolation system is important in bridges design, primarily in seismically active countries. Bridges are prone to damage from seismic forces. Elastomeric isolation bearings have been applied in short-span bridges for some time in most countries. These bearings are preferred because of the low maintenance cost. However, these bearings are not reliable when subjected to large displacement and low temperatures. In the other hand, friction sliding bearings shows better performance under the former circumstances despite its use is still limited to long-span bridges and has not been explored further. This paper describes a performance evaluation of seismically-isolated short-span reinforced concrete bridge using friction pendulum system (FPS). Seismic performances of non-isolated and isolated models from the reference bridge functioning as light rapid transit (LRT) bridge in Jakarta are investigated using nonlinear time history analysis. The results demonstrate that isolated bridges with FPS performed better than non-isolated bridges under 1000-year earthquake as shown by reductions of base shear force, absolute deck acceleration, and acceleration amplification ratio. Comparisons of isolated bridges with different FPS friction types and arrangement have demonstrated that the reference bridge with all Type A friction (�0 = 0.050) applied, performed the best among all other configurations.

Nonlinear Dynamic Analysis of Seismically Base-Isolated Structures by a Novel OpenSees Hysteretic Material Model

The complex response characterizing elastomeric isolation bearings is reproduced by employing a novel uniaxial hysteretic model that has been recently formulated and successfully implemented in OpenSees. Such a novel OpenSees material model offers several advantages with respect to differential models typically available in commercial software products for structural analysis, such as 3D-BASIS and CSi programs. Firstly, it is based on a set of only five model parameters that have a clear mechanical significance; such a property not only allows one to drastically simplify the parameters identification process, but it also allows the model to be used in practice. In addition, the model does not require numerical methods for the evaluation of the restoring force since the latter is computed by solving an algebraic equation. To encourage researchers and designers to adopt the proposed model for research and practical purposes, we demonstrate its accuracy by performing some numerical tests in OpenSees. In particular, we first employ the recently implemented model to compute the nonlinear dynamic response of a seismically base-isolated structure with elastomeric bearings and, subsequently, we compare the results with those obtained by modeling the seismic isolators with the OpenSees BoucWen uniaxial material model, that is one of the most popular and accurate hysteretic models currently available in OpenSees.

Seismic responses of multi-story building isolated by Lead-Rubber Bearings considering effects of the vertical stiffness and buckling behaviors

Elastomeric isolation bearing is one of the most commonly efficient devices and widely applied for protecting constructions in the earthquake regions. Its significant lateral deformation during operation, however, may affect its load-carrying capacity, especially the stability of the bearing. The current preliminary design method often focuses on shear behavior without effects of vertical stiffness and stability conditions that do not reflect the practical operation of devices. The paper presents the effect of vertical stiffness and buckling behavior on the seismic performance of lead-rubber bearing (LRB) used for seismic isolation in multi-story buildings. The effective parameters of LRB are estimated by the single-mode spectral analysis method, through a bilinear model, calculated by a typical target spectrum of Eurocode 8. A two-spring equivalent model is employed to study the effects of the vertical stiffness and critical buckling load that is varied as a function of lateral deformation. A set of time history nonlinear analysis is conducted to investigate the effects of vertical stiffness and critical buckling load on the seismic responses of building structures. The findings show the taking into account of the vertical stiffness and buckling behavior results in an increase of lateral displacements and a decrease of the lateral force and the floor acceleration of the isolated building.

Probabilistic Seismic Resilience-Based Cost–Benefit Analysis for Bridge Retrofit Assessment

This paper explores a probabilistic resilience-based cost–benefit model that can be used to identify the best retrofit measures for bridges. In the model, the increase in resilience is considered to be the benefit of seismic retrofit. A bridge functionality assessment model is also proposed to evaluate resilience. The functionality is estimated based on the appropriate seismic loss and exponential recovery function models. Then, the functionality assessment model is validated with the field data of the post-earthquake recovery process of bridges. The whole proposed methodology is applied to a non-seismically designed multi-span simply supported concrete girder bridge located in Charleston. Seven retrofit measures, including steel jackets, seat extenders and elastomeric isolation bearings, are applied to the as-built bridge in order to assess their cost-effectiveness. The results show that the cost-effectiveness of retrofit measures varies with the ground motion intensity, and the best retrofit is seat extenders followed by elastomeric isolation bearings when considering the seismic hazard of Charleston. Sensitivity analysis is also performed to identify major uncertain parameters to which the resilience-based cost–benefit ratios are most sensitive. Statistical analysis of resilience-based cost–benefit ratios obtained through random sampling of major uncertain parameters reveals that normal distribution can be used to describe their uncertain nature. The 90% confidence intervals of resilience-based cost–benefit ratios estimated from random sampling also indicate the high cost-effectiveness of seat extenders and elastomeric isolation bearings to enhance bridge performance.

Improved nonlinear rotational constitutive law for predicting critical loads in elastomeric isolation bearings

Abstract Predicting critical loads in elastomeric isolation bearings has important implications for the design of isolation systems. The key mechanism for predicting the critical loads is to precisely predict the nonlinear rotational properties of the bearings. However, most of the existing rotational constitutive laws of elastomeric bearings are divided into linear stage and nonlinear stage. The predicted critical loads from these piecewise models lead to inaccurate results compared to experimental observations. In this paper, the basic assumptions of previous researches are extended considering the nonlinear properties of bonded rubber layer. On the basis, an improved nonlinear rotational constitutive law is proposed. The improved model can provide a continuous prediction of critical loads throughout the horizontal displacements. The calculated critical loads are confirmed by comparison with existing test data.

Seismic fragility assessment of a multi-span RC bridge in Bangladesh considering near-fault, far-field and long duration ground motions

Seismic vulnerability of a three-span continuous highway bridge located in Kishoreganj, Bangladesh is assessed numerically in this study. Fragility curves have been derived from the nonlinear incremental dynamic analysis results of the bridge subjected to medium to strong near-fault, far-field and long duration ground motions. This study aims to investigate the damage probability of bridge components (piers and isolation bearings) and the bridge system under different types of ground motions. A total of 48 near-fault, far-field, and long duration ground motion records with peak ground acceleration values ranging from 0.08 g to 2.31 g are used in the nonlinear dynamic analysis of the bridge. A 3-D finite element model scheme is used in this study considering nonlinearity in the bridge piers and the elastomeric isolation bearings. The fragility curves are constructed for two bridge components (i.e., piers and isolation bearings), and the system as well. The numerical results show that both component levels and bridge system failure probabilities are dominated by long duration ground motions than those of near-fault and far-field ground motions.

Experimental Investigation of Elastomeric Isolation Bearings with Flexible Supporting Columns

AbstractIn an effort to mitigate major costs associated with isolation systems, especially in retrofit applications, isolation bearings may be placed on the tops of columns. In this configuration, ...

Implementation of a Simplified Method in Design of Hysteretic Dampers for Isolated Highway Bridges

AbstractUsing seismic isolation systems for highway bridges modifies the structure’s principal vibration modes and effectively reduces the seismic base shear conveyed from the superstructure to the substructure. However, for some low-damping rubber isolation bearings, large displacements can be a problem. Supplemental hysteretic dampers can be introduced into the base-isolated bridge, which might nevertheless increase the structure base shear, and the merit of adding dampers has to be evaluated properly. In this paper, a simplified method was implemented for the design of a low-cost hysteretic damper, and the resulting isolator-damper system was tested experimentally. The design method used is based on an equivalent linearization approach. A full-scale elastomeric isolation bearing was characterized and used in the design of a hysteretic damper. Both the isolator and the damper went through cyclic testing and real-time dynamic substructuring (RTDS) methods to verify the capacity of the method to design ba...

Performance of steel mesh reinforced elastomeric isolation bearing: Experimental study

This paper developed a new type of elastomeric isolation bearings, of which the reinforcing element is manufactured by high-strength steel mesh. In order to investigate the compressive and shear deformation performance of the new system, eight full-scale steel mesh reinforced elastomeric isolation bearings (SMREIB) with details partly referring to current Chinese standard were studied by static experiment. Then quasi-static tests were carried out to compare the performance of both SMREIB and traditional bearings. Parametric tests were made under combined axial compression and reversed cyclic lateral displacement. Test parameters, including vertical compression, shear strain magnitude, loading frequency, loading waveform and loading direction, were investigated. The constitutive model and hysteresis energy dissipation capability of bearings were figured out. The experimental results indicate that the ultimate shear deformation of SMREIB can reach 300% total bearing height, which exceeds Chinese standard limits of 100% total rubber thickness, by rolling-off and rolling-over deformation, and its horizontal equivalent stiffness gets lower. Larger total rubber thickness, which is the main advantages of SMREIB, affects the horizontal mechanic property and hysteresis energy dissipation capability of bearing. Experimental result provides us the basis for the development of numerical model, which can help engineers design and apply SMREIB in the practical bridges.

Investigation of the seismic response of high‐rise buildings supported on tension‐resistant elastomeric isolation bearings

SummaryIn many applications of seismic isolation, such as in high‐rise construction, lightweight construction, and structures with large height‐to‐width aspect ratios, significant tension forces can develop in bearings, raising concerns about the possible rupture of elastomeric bearings and the uplift of sliding bearings. In this paper, a novel tension‐resistant lead plug rubber bearing (TLRB) with improved tension‐resisting capabilities is developed and experimentally and numerically assessed. This TLRB consists of a common lead plug rubber bearing (LRB) and several helical springs. After describing the theory underlying the behavior of the TLRB, the mechanical properties of reduced‐scale prototype bearings are investigated through extensive horizontal and vertical loading tests. The test results indicate that TLRBs can improve the shear stiffness and tension resistance capacity even under significant tensile loads. A series of shaking table tests on scaled models of high‐rise buildings with different aspect ratios were conducted to investigate the dynamic performance of the TLRB and the seismic responses of base‐isolated high‐rise buildings. Three different cases were considered in the shaking table tests: a fixed base condition and the use of TLRB and LRB isolation systems. The results of the shaking table test show that (a) base‐isolated systems are effective in reducing the structural responses of high‐rise buildings; (b) an isolated structure's aspect ratio is an important factor influencing its dynamic response; (c) TLRBs can endure large tensile stresses and avoid rupture on rubber bearings under strong earthquakes; and (d) the experimental and numerical results of the responses of the models show good agreement. Copyright © 2016 John Wiley & Sons, Ltd.

多重動吸振器を用いた免震橋の桁応答変位の低減

多重動吸振器を用いた免震橋の桁応答変位の低減

An advanced numerical model of elastomeric seismic isolation bearings

SUMMARYThe nuclear accident at Fukushima Daiichi in March 2011 has led the nuclear community to consider seismic isolation for new large light water and small modular reactors to withstand the effects of beyond design basis loadings, including extreme earthquakes. The United States Nuclear Regulatory Commission is sponsoring a research project that will quantify the response of low damping rubber (LDR) and lead rubber (LR) bearings under loadings associated with extreme earthquakes. Under design basis loadings, the response of an elastomeric bearing is not expected to deviate from well‐established numerical models, and bearings are not expected to experience net tension. However, under extended or beyond design basis shaking, elastomer shear strains may exceed 300% in regions of high seismic hazard, bearings may experience net tension, the compression and tension stiffness will be affected by isolator lateral displacement, and the properties of the lead core in LR bearings will degrade in the short‐term because of substantial energy dissipation.New mathematical models of LDR and LR bearings are presented for the analysis of base isolated structures under design and beyond design basis shaking, explicitly considering both the effects of lateral displacement and cyclic vertical and horizontal loading. These mathematical models extend the available formulations in shear and compression. Phenomenological models are presented to describe the behavior of elastomeric isolation bearings in tension, including the cavitation and post‐cavitation behavior. The elastic mechanical properties make use of the two‐spring model. Strength degradation of LR bearing under cyclic shear loading due to heating of lead core is incorporated. The bilinear area reduction method is used to include variation of critical buckling load capacity with lateral displacement. The numerical models are coded in OpenSees, and the results of numerical analysis are compared with test data. The effect of different parameters on the response is investigated through a series of analyses. Copyright © 2014 John Wiley & Sons, Ltd.

Numerical Analysis of Seismic Elastomeric Isolation Bearing in the Base-Isolated Buildings

Base isolation concept is currently accepted as a new strategy for earthquake resistance structures. According to different types of base isolation devices, laminated rubber bearing which is made by thin layers of steel shims bonded by rubber is one of the most popular devices to reduce the effects of earthquake in the buildings. Laminated rubber bearings should be protected against failure or instability because failure of isolation devices may cause serious damage on the structures. Hence, the prediction of the behaviour of the laminated rubber bearing with different properties is essential in the design of a seismic bearing. In this paper, a finite element modeling of the laminated rubber bearing is presented. The procedures of modeling the rubber bearing with finite element are described. By the comparison of the numerical and the experimental, the validities of modelling and results have been determined. The results of this study perform that there is a good agreement between finite element analysis and experimental results.

鉛プラグ入り積層ゴムの水平二方向復元力特性に関する研究

Reduction of the horizontal deformation capacity of elastomeric isolation bearings under bi-directional loading has been one of the major concerns since that such a phenomenon was observed for high-damping rubber bearings. Using a newly constructed loading machine, a series of tests of lead rubber bearings (LRBs) were conducted to investigate their detailed mechanical characteristics under horizontal bi-directional deformation in the paper. The influences of the configurations, such as shape of cross section, diameter of a lead plug and aspect ratio, on the bi-directional behavior were carefully examined. Simulation analyses were also conducted to predict the bi-directional behavior of LRBs.

P-Δ and End Rotation Effects on the Influence of Mechanical Properties of Elastomeric Isolation Bearings

Seismic isolation systems constitute an accepted and simple technique for earthquake protection of structural systems and sensitive components. This approach has considerable potential in preventing the structures and their equipment from earthquake destruction. For predicting the behavior of an isolation bearing, Haringx’s theory is usually employed. According to this theory, the mechanical properties of an elastomeric isolation bearing can be predicted and described. Many investigators have proposed a nonlinear, mechanical model for multilayer elastomeric bearings. However, in previous theoretical and experimental studies, the effects of initial rotation at the ends of the bearings have been neglected. In this study, Haringx’s theory is extended and an analytical method is presented by considering the initial rotations of the upper and lower ends of multilayer rubber bearings as new boundary conditions. Three boundary conditions have been considered for modeling the elastomeric isolation bearing: (1) equal rotation at the bottom and top end of a bearing, (2) rotation only at the bottom end, and (3) rotation only at the top end of a bearing. According to these boundary conditions, variations of the lateral displacement and interior rotation of the laminated rubber bearings are obtained. The variations of horizontal stiffness, internal bending moment, and interior shear force of the bearing have also been presented. Examples are presented to demonstrate the validity of the development method in predicting the mechanical properties of elastomeric bearings with specified geometric parameters. The results of this study have shown that initial rotation as a boundary condition will change the mechanical properties of the laminated rubber bearings.

Stability of Elastomeric and Lead-Rubber Seismic Isolation Bearings

Elastomeric and lead-rubber bearings are two commonly used types of seismic isolation devices. During seismic events, some of the bearings in an isolation system will be subjected to large axial compressive loads, caused by gravity plus overturning forces, accompanied by simultaneous large lateral displacements. However, the critical load capacity of elastomeric bearings has been shown to reduce with increasing lateral displacement. The design of isolation systems composed of these types of bearings therefore requires that stability at the maximum displacement be demonstrated. The current procedure to assess the stability uses a ratio of areas, referred to as the overlapping area method, to determine the critical load capacity at a given lateral displacement that must be greater than a combination of axial forces imposed on the bearing. Although the overlapping area method provides a simple means of calculating the critical load at a given lateral displacement, it lacks a rigorous theoretical basis and ha...

Three‐dimensional analysis for square seismic isolation bearings under large shear deformations and high axial loads

AbstractSquare seismic isolation bearings are economical to manufacture, offer the advantage of simple connection configurations and have compact geometry requiring a minimum of space for installation. To be able to more effectively utilize square bearings for seismic isolation systems, a new mechanical model for predicting the large shear deformation behavior of square elastomeric isolation bearings is presented in this paper. The new model is developed by extending to three dimensions an existing model for elastomeric isolation bearings under severe axial loads and shear deformations. The model comprises multiple shear springs at the mid‐height and a series of axial springs at the top and bottom boundaries. Static loading tests of square lead–rubber isolation bearings were performed to investigate the influence of horizontal loading direction and axial load magnitude on bearing behavior. The test results showed that the ultimate behavior is strongly influenced by loading direction, especially under large shear deformation and high axial load. To confirm the validity of the model, analyses are performed of the loading tests of the square lead–rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.

Evaluation of response displacement reduction effect by TMD application to a bridge girder supported by elastomeric isolation bearings

橋梁の地震時性能を確保するため水平力分散支承や免震支承を用いた橋梁形式がしばしば採用されているが，こうした構造では免震支承のエネルギー吸収性能を考慮しても，地震時に上部構造において大きな変位が生じることを前提とした設計が必要となる．しかしながら，大きな遊間を設けることでそうした相対変位を許容した場合，建設コストや維持管理，走行性等の問題要因となる．こうした橋梁における相対変位を抑制する方策として，免震支承等で支持された上部構造である橋桁に同調質量ダンパー(TMD)を適用する方法に関して検討を行った．強震時の効果の向上を図るため免震支承として用いられる積層ゴム支承の非線形性を考慮した同調条件を求め，弾性応答を仮定した同調パラメータとの相違を示すとともに，地震時の桁変位の低減効果はTMDと桁の質量比が10%程度までの範囲で大きな地震時桁変位低減効果が得られる場合があることを数値シミュレーションにより示した．

A mechanical model for elastomeric seismic isolation bearings including the influence of axial load

AbstractFor the purpose of predicting the large‐displacement response of seismically isolated buildings, an analytical model for elastomeric isolation bearings is proposed. The model comprises shear and axial springs and a series of axial springs at the top and bottom boundaries. The properties of elastomeric bearings vary with the imposed vertical load. At large shear deformations, elastomeric bearings exhibit stiffening behavior under low axial stress and buckling under high axial stress. These properties depend on the interaction between the shear and axial forces. The proposed model includes interaction between shear and axial forces, nonlinear hysteresis, and dependence on axial stress. To confirm the validity of the model, analyses are performed for actual static loading tests of lead–rubber isolation bearings. The results of analyses using the new model show very good agreement with the experimental results. Seismic response analyses with the new model are also conducted to demonstrate the behavior of isolated buildings under severe earthquake excitations. The results obtained from the analyses with the new model differ in some cases from those given by existing models. Copyright © 2008 John Wiley & Sons, Ltd.

Three-dimensional nonlinear seismic performance evaluation of retrofit measures for typical steel girder bridges

Steel girder bridges are common bridges in North America which have exhibited considerable vulnerabilities in past earthquake events. This paper conducts nonlinear time history analysis using detailed three-dimensional models of typical multi-span simply supported and multi-span continuous steel girder bridges to evaluate the effectiveness of various retrofit strategies. Restrainer cables, steel jackets, shear keys, and elastomeric isolation bearings are assessed for their influence on the variability and peak longitudinal and transverse response of critical components in the bridges. The results indicate that different retrofit measures may be more effective for each class of bridges. For example, the restrainer cables are effective for the multi-span simply supported (MSSS) bridge, yet not the multi-span continuous (MSC) bridge; shear keys improve the transverse bearing response in the MSC bridge but are not effective in the MSSS bridge which exhibits less transverse vulnerability; and elastomeric bearings improve the response of the vulnerable columns in both the MSSS and MSC bridges yet lead to increased abutment demands in the MSC bridge. The study reveals that while a retrofit may have a positive influence on the targeted component, other critical components may be unaffected or negatively impacted. This lends support to vulnerability assessments that consider the impact of retrofit on system vulnerability reflecting the contribution of multiple components.