Laminated Rubber Bearings Research Articles

Seismic Response Analysis and Evaluation of Laminated Rubber Bearing Supported Bridge Based on the Artificial Neural Network

Laminated rubber bearings are commonly adopted in small‐to‐medium span highway bridges in earthquake‐prone areas. The accurate establishment of the mechanical model of laminated rubber bearings is one of most critical steps for the bridge seismic response analysis. A new constitutive model of bearing based on the artificial neural network (ANN) technique is established through the static cyclic test of laminated rubber bearings, considering the bearing initial stiffness, friction coefficient, and other parameters such as the bearing sectional area, height, loading velocity, vertical load, and aging time. Combined with the ANN method, the ANN‐based bridge seismic demand model is built and applied to the rapid evaluation of the bridge seismic damage. The importance of the bearing affecting design factors in the bridge seismic demands are ranked. The results demonstrated that the dimensions of the bearing and vertical load are the main factors affecting the bearings constitutive model. Based on the partial dependency analysis with the ANN‐based bridge seismic demand model, it is concluded that the height of bearing is the key design parameter which affects the bridge seismic response the most. The ANN seismic demands model can fit the complex function relationship between various factors and bridge seismic response with high precision, so as to achieve the rapid evaluation of bridge seismic damage.

Multihazard Response Control of Base-Isolated Buildings under Bidirectional Dynamic Excitation

The issues of safety and posthazard functionality of structures under multihazard scenarios are some of the significant challenges in the current dynamic and rapidly growing urban environment. In this paper, multistory base-isolated buildings are investigated under the independent multihazard scenario of earthquake and blast-induced ground motion (BIGM). Multistory building models equipped with five different types of isolation systems, namely, the laminated rubber bearing (LRB), lead-rubber bearing (N-Z system), pure friction (PF) system, friction pendulum system (FPS), and resilient-friction base isolator (R-FBI) are assessed under bidirectional multihazard excitations. The suitability of the isolation systems and their key parameters in protecting multistory buildings is evaluated. Furthermore, the influence of the superstructure characteristics, such as the superstructure damping and the number of stories, is also assessed. The effect of bidirectional hazards on fixed-base buildings is also presented for comparison. The key response quantities of base-isolated buildings are presented and compared for different isolation systems. Parametric investigations are also conducted, and the trends of the response quantities are presented to study the influence of important parameters of isolation systems in protecting the buildings under the multihazard scenario of earthquake and BIGM. The results of the investigation show that the behaviors of the buildings equipped with various isolation systems are different for the two hazards. Moreover, the influences of the key parameters of the isolation systems are found to be different for various hazards. Therefore, the selection of design parameters of isolation systems shall be made with due consideration of the influence of multiple hazards. Additionally, the influence of the properties of the superstructure, such as the number of stories and the damping of the superstructure, on the behavior of the base-isolated buildings under the multihazard loading, is presented.

A parametric study on the stability of fiber reinforced rubber bearings under combined axial and shear loads

Fiber Reinforced Bearings (FRBs) have proven to be a valuable rubber-based base isolation technology in which flexible fiber reinforcements are used to replace the steel layers commonly adopted for the manufacturing of Laminated Rubber Bearings (LRBs). Thanks to the low weight and cost of FRBs, these devices could prove to be instrumental for the promotion of base isolation applications to houses and residential buildings of developing countries of the world in seismic regions. This study is based on the results of a large set of Finite Element Analyses (FEAs) aimed to assessing the performance of FRBs under combined axial and shear loads. The aim of this work is that of filling a lack of knowledge regarding the lateral displacement capacity of FRBs: research studies available in literature do not consider the effects of axial pressure, material properties, primary and secondary shape factors on the response of these devices under combined axial and lateral loads. Conclusions of this study underline that the simple design formula commonly adopted for the design of FRBs underestimate the effect of the axial pressure in limiting the lateral displacement capacity of the bearings. Moreover, available simplified formula, do not offer an accurate estimate of the force response of these bearings under combined loads. Additional FEAs are needed to extend the results of this study to bearings of other shapes, including circular and square isolators.

Evaluation of mechanical properties considering hysteresis characteristic of high damping rubber bearing

Recently, laminated rubber bearings are widely used as seismic isolators for road bridges. Although many studies have been conducted on the dynamic model of High Damping Rubber (HDR) bearings, few models can reflect phenomena such as the dependency of experienced shear strain on initial history. To develop a model that can represent the dependency of the experienced shear strain of HDR and a dynamic loading test was conducted using HDR specimens. The hysteresis characteristics of HDR was measured by applying a horizontal vibration using a hybrid actuator under a constant vertical load. Based on the cyclic shear test, the mechanical properties of HDR were calculated such as absorbed energy, hysteresis loop area, equivalent stiffness, equivalent damping ratio. Dynamic analysis was also performed from the experimental results. The dynamic model applied in program analysis is a bilinear type double-target model. This model can express the nonlinear characteristics related to the initial history of HDR bearings. The parameters required for dynamic analysis were determined from the experimental results. Through this dynamic analysis, the effectiveness of the bilinear type double target model was verified. In this research, a high damping rubber specimen was used.

Stiffness Identification Method of Simply Elastic Supported Beam based on First-order Modal Rayleigh Solution

In order to evaluate the support state of bridges with elastic supports, based on first-order mode Rayleigh solution, a stiffness identification method of elastic supports beam is proposed. The superposition displacement of static displacement and rigid body displacement under sinusoidal load is used as the vibration mode function. Based on the mode function, the calculation formula of the fundamental frequency for the simply supported elastic support beam is derived according to the Rayleigh method. The identification method of the support stiffness and beam stiffness of the elastic support beam is derived by using the measured frequency and the mode value. A precast box girder is analyzed by an example. According to the measured results and finite element results, the stiffness of the precast box girder and the stiffness of the laminated rubber bearing are identified by the stiffness identification method established.

Analysis of time-dependent seismic fragility of the offshore bridge under the action of scour and chloride ion corrosion

This study uses the time-dependent fragility analysis method, based on the Duracrete model and previous experimental results, to determine the probability distribution types and statistical characteristics of various environmental parameters and corrosion parameters. In this paper, an analysis framework is proposed to study the seismic fragility of bridges under the action of chloride ion corrosion and scour. With the increase of scour depth, the seismic fragility of the bridge in the example shows nonlinear growth, and the fragility of the laminated rubber bearing is higher than that of the pier, which makes the laminated rubber bearing sustain more significant damage than the pier when the earthquake occurs, thus playing the role of a “fuse” and reducing the seismic damage of the pier. Based on the Duracrete model, the degradation law of reinforced concrete performance with time was obtained by the Monte Carlo method under a chloride ion corrosion environment. Compared with the apparent increase of bridge pier fragility, the fragility change of the laminated rubber bearing was not noticeable and showed a trend of increasing first and then decreasing. Under the combined action of chloride ion corrosion and scour, the seismic fragility of the laminated rubber bearing in the early service stage of the bridge is dramatically higher than that of the pier, which leads to the laminated rubber bearing being damaged before the pier to protect the pier in the case of an earthquake. With the increase of service time, the seismic fragility of the pier is gradually higher than that of the laminated rubber bearing, which becomes a weak link in the anti-seismic system of bridges.

Fundamental study on seismic safety margin for seismic isolated structure using the laminated rubber bearings

Fundamental study on seismic safety margin for seismic isolated structure using the laminated rubber bearings

Preliminary research on Risk Assessment of Seismic Isolation system considering ultimate characteristics of laminated rubber bearing

Preliminary research on Risk Assessment of Seismic Isolation system considering ultimate characteristics of laminated rubber bearing

Effects of Shape Memory Alloys on Response of Steel Structural Buildings within Near Field Earthquakes Zone

Base isolation is one of the effective ways for controlling civil engineering structures in seismic zone which can reduce seismic demand. Also is an efficient passive control mechanism that protects its superstructure during an earthquake. However, residual displacement of base-isolation systems, resulting from strong ground motions, remain as the main obstacle in such system’s serviceability after the earthquake. Shape Memory Alloys (SMA) is amongst the newly introduced smart materials that can undergo large nonlinear deformations with considerable dissipation of energy without having any permanent displacement afterward. This property of SMA may be utilized for designing of base isolation system to increase the structure’s serviceability. Here, a proposed semi-active isolation system combines laminated rubber bearing system with shape memory alloy, to take advantage of SMAs high elastic strain range, in order to reduce residual displacements of the laminated rubber bearing. Merits of the system are demonstrated by comparing it to common laminated rubber bearing isolation systems. It is found that the optimal application of SMAs in base-isolation systems can significantly reduce bearings’ residual displacements. In this study, OpenSees program for a three dimensional six-storey steel frame building has been used by locating the isolators under the columns for investigating the feasibility of smart base isolation systems, i.e., the combination of traditional Laminated Rubber Bearing (LRB) with the SMA, in reducing the structure’s isolated-base response to near field earthquake records are examined. Also, a new configuration of SMAs in conjunction with LRB is considered which make the system easier to operate and maintain.

Vibration Response Simulation on a High Risk Building with Laminated Rubber Bearing Base Isolation Subjected to Earthquake Excitation

In a high risk building like hospitals, laboratories, or school, the response of the building due to earthquake might be very dangerous. To reduce victims and damages in infrastructure, a type of base isolation is installed to the foundation of the building. The base isolation, in form of a laminated rubber bearing, produces a horizontal movement of the structure when subjected to earthquake forces in order to keep the people and equipment safe. Some calculations of the response vibration parameters are observed to determine the optimal characteristics of the base isolation. The Keq Value is 415,120,000 N/m and the total mass of the building is 739,534,249.7 kg as well as the highest vibration force is 4,015,079,348.47 N. The aim of this research is to simulate the lateral motion of the building with base isolation, due to earthquake forces and decide whether the response is as expected of the design.

New structural seismic protection for high-rise building structures

Presented Structural Seismic Isolation Method (SSIM) aims to provide high safety for Highly Reliable Structures (HRS) against strong earthquakes including near-fault and long-period ground motions. The examined structure is converted to Structural Seismic Isolation System (SSIS) by the SSIM method which exhibited inverse pendulum behaviour. For this purpose, structure foot base and foundation contact surfaces have been designed as any curved surfaces (spherical, elliptical, etc.) depending on the earthquake-soil-superstructure parameters and this contact surfaces have been separated by elastomeric (lead core rubber or laminated rubber bearings) seismic isolation devices. It would allow the structure foot base to turn around gyration centre through rubber bearing contact and maintains similar behaviour to the super-structure. SSIS system provides the possibility of keeping the natural-period of the structure in a larger interval, which is greater than the predominant-period of the majority of possible earthquakes (including near-fault pulse) using currently existing conventional elastomeric isolators with up to 4 second period. Thus, the structure can sustain its serviceability after strong and long-period earthquakes. In this study SSIS system’s performance is presented for high-rise building structures, for this aim, the finite element model of the building (Bg) structure with SSIS system (SSIS-Bg) has been prepared and the nonlinear dynamic analysis of the model has been conducted using strong and long-period ground motions. Results indicate that the base and top accelerations, base shear and base moment responses of the SSIS-Bg structure is 23.21 %, 75.47 % and 85.74 % in average lower than the Conventional Application Method of Seismic Base Isolation Devices for Building (CAMSBID-Bg) structures respectively and it is not prone to resonant vibrations under long-period earthquakes related with the excessive deformation in the isolation layers in case of using CAMSBID-Bg structures. It should be noted that in this study with the presented SSIM method and SSIS system, it is aimed to protect only the Highly Reliable Structures(HRS) from the effects of strong and long-period ground motions and these structures (HRS) are classified as follows: 1) Nuclear Containment Structures; 2) High-rise buildings that contain information, operating systems, sensitive instruments, communication systems, routing systems, bank operating systems, databases, management systems and other similar facilities that are linked to the security and economy of a country; 3) High-rise hospitals etc.

Development of Small-Sized Lead Inserted Laminated Rubber Bearing for Nuclear Component Seismic Isolation

This paper presents a design specification of the small-sized lead inserted laminated rubber bearing (LRB) for application to nuclear component seismic isolation and describes the results of test verification on design performance parameters such as effective horizontal stiffness, equivalent viscous damping ratio, design seismic isolation frequency, and ultimate shear deformation. To do this, two types of LRB, having the same vertical design load of 10 kN but with different shape factors, are designed, fabricated, and tested by the quasi-static procedures. To determine the effective horizontal stiffness and the equivalent damping value from the test results, the new method is proposed and compared with the methods of the ASCE and ISO standards in case that the tangential stiffness curve is not linear in tests. From the comparison between tests and design specifications in the performance parameters, it was found that the design specifications developed in this paper are in a good agreement with the test results. Furthermore, the target design shear deformation limits are confirmed to have sufficient design margins in ultimate shear deformation tests.

Assessing the three-dimensional seismic behavior of the multi-degree-of-freedom (MDOF) structure with LCRB and LRB control systems

The main objective of this study was to investigate the dynamic behavior of isolated structures with lead core rubber bearing (LCRB) and laminated rubber bearing (LRB) isolators under the influence of different earthquakes. First, a three-dimensional finite element model of the seismic isolator was created and analyzed using ABAQUS software based on a developed model. The hyper-viscoelastic properties were used for rubber layers in this modeling. Then, a 5-story base-isolated building on a laboratory scale was modeled on a well-verified isolator, which was once with core (LCRB) and then without the core (LRB). In this study, the isolation system was analyzed by dynamic explicit approach in ABAQUS and the behavior of the considered isolated building has been studied when subjected to Kobe, Northridge, and El Centro earthquakes. Finally, it was found that LCRB has a significant effect on reducing the amount of displacement and acceleration in the upper floors. However, it should be noted that the responses of the base-isolated building may unexpectedly appear reversely in some earthquakes and increase the responses.

New Structural Seismic Isolation for Nuclear Containment Structures

The new Structural Seismic Isolation System (SSIS) intends to provide high safety for important structures such as nuclear power plants, offshore oil platforms, and high-rise buildings against near-fault and long-period earthquakes. The presented SSIS structure foot base and foundation contact surfaces have been designed as any curved surfaces (spherical, elliptical, etc.) depending on the earthquake-soil-superstructure parameters, and these contact surfaces have been separated by using elastomeric (lead core rubber or laminated rubber bearings with up to 4-second period) seismic isolation devices. It would allow providing inverse pendulum behavior to the structure. As a result of this behavior, the natural period of the structure will possess greater intervals which are larger than the predominant period of the majority of the possible earthquakes including near-fault zones. Consequently, the structure can maintain its serviceability after the occurrence of strong and long-period earthquakes. This study has investigated the performance of the SSIS for the nuclear containment (SSIS-NC) structure. The finite element model of SISS-NC structure has been developed, and nonlinear dynamic analysis of the model has been conducted under the strong and long-period ground motions. The results have been presented in comparison with the conventional application method of the seismic base isolation devices for nuclear containment (CAMSBID-NC) and fixed base nuclear containment (FB-NC) structures. The base and top accelerations, effective stress, and critical shear stress responses of the SSIS-NC structure are 48.67%, 36.70%, and 32.60% on average lower than those of CAMSBID-NC structure, respectively. The result also confirms that the SSIS-NC structure did not cause resonant vibrations under long-period earthquakes. On the other hand, there is excessive deformation in the isolation layers of CAMSBID-NC structure.

Shake table tests of highway bridges installed with unbonded steel mesh reinforced rubber bearings

Previous earthquakes in China have caused significant seismic damage in short-to-medium span highway bridges due to the uncontrollable sliding of unbonded laminated rubber bearings (ULNRs). This paper investigates the soundness of replacing the ULNRs in these bridges with novel unbonded steel mesh reinforced rubber bearings (USRBs). Distinct from ULNRs that use rigid steel plates, USRBs are reinforced by flexible high-strength steel meshes to enable large and stable rollover deformations when subjected to strong earthquakes. To this end, shake table tests have been carried out for a two-span steel girder bridge that is isolated by ULNRs and USRBs, respectively. The test bridge was designed with a scale factor of 1/15 by maintaining the similarity of the deck mass, pier longitudinal stiffness, and bearing lateral stiffness for a typical prototype bridge in high seismic zones in China. Various types of sensors were used to monitor the dynamic responses of the bridge when excited by four different sets of earthquake motions. Test results show that USRBs not only exhibit a higher isolation efficiency in limiting the deck inertia force, but also outperform ULNRs in controlling the sliding of the bearings. Moreover, a phenomenological material model is utilized to simulate the hysteretic behavior of the USRBs, where the bridge’s time-history responses have been validated against the experimental outcomes. This paper illustrates that the use of USRBs can be a cost-effective, robust, and reliable substitute for the ULNRs to enhance the seismic resilience of the transportation infrastructure in China.

Rural Masonry Isolating Structure and LRB Experiment: Seismic Resistance Properties and Statistical Data Curve Analyses

The low masonry structure is the most commonly applied building type in rural China. It is possible to install small‐diameter, low cost, and easily constructed laminated rubber bearing (LRB) components. Isolation technology has broad application prospects in rural buildings. We developed a small‐diameter LRB in this study wherein the isolation layer is set above the floor for easy installation and replacement. We built and tested 4 walls to observe the effects of different LRB thicknesses; we assessed test respective phenomena and seismic parameters accordingly. We ran another test on five small‐diameter LRB components with varying horizontal stiffness, different forms of shear strain‐equivalent horizontal stiffness, and postyield stiffness while changing the fitting formula for the second shape coefficient to give small‐diameter LRB design providing gist.

Seismic Study of Skew Bridge Supported on Laminated‐Rubber Bearings

Skew bridges consisting of simply supported girders, continuous decks, and laminated‐rubber bearings are widely used in western China; however, they are highly vulnerable to strong earthquakes. To investigate the seismic performance of skew bridges considering the sliding behavior of laminated‐rubber bearings, the Duxiufeng Bridge located in Sichuan, China, was used as a prototype bridge. This bridge is a skew bridge that suffered seismic damage during the 2008 Wenchuan earthquake. The possible seismic response of this skew bridge under the Wenchuan earthquake was simulated, and the postearthquake repair methods were analyzed considering the effects of bearing types and cable restrainers. Parametric studies, using the finite element method, were also performed to investigate the effects of the skew angle and friction coefficient of the bearings on the seismic response of the skew bridge. The results indicate that pin‐free bearings could effectively control the seismic displacement of the bridge, and the cable restrainers with an appropriate stiffness could significantly reduce the longitudinal residual displacements. The effect of skew angles is less significant on skew bridges with laminated‐rubber bearings than on rigid‐frame skew bridges because of the sliding between the girders and bearings. The residual displacements of the bearings were more sensitive to the variation in the friction coefficient between the laminated‐rubber bearings and the girders compared to the maximum seismic displacements.

Performance and Material Characteristics of 30 years Use Laminated Rubber Bearings for Seismic Isolation of Buildings

Performance and Material Characteristics of 30 years Use Laminated Rubber Bearings for Seismic Isolation of Buildings

Research on Numerical Simulation of Laminated Rubber Bearing

Based on the test of laminated rubber bearing GYZ250*77 in the literature, the finite element analysis model of the bearing is established by using ANSYS analysis software. The bearing force can be calculated by considering different modeling methods and different load application methods, and the analysis results are compared with the test results. The results show that when the laminated rubber bearing performance is simulated and analyzed under vertical loads, the rigid zone loading method or the steel plate loading method should be selected according to the specific conditions, rather than the direct loading method; Both solid model analysis and plane model analysis can simulate the effect of vertical load on the laminated rubber bearing. The research results provide a reference for the numerical simulation analysis of the laminated rubber bearing.

Rayleigh Damping Coefficients of Laminated Rubber Bearing

In isolating the ground structure and the above ground structure from seismic loads, a significant device called laminated rubber bearing is usually found in structure. The complexity of the material which is made up from a combination of rubber and steel shim plates in alternate layer, has made it difficult to measure damping value. Damping is a dissipation of energy or energy losses in the vibration of the structure. Measuring the accurate amount of damping is fundamental as damping plays a crucial role in fixing the borderline between stability and instability in structural systems. Therefore, to determine the damping value including dynamic properties in any materials, modal analysis can be used. Hence, the main objective of this research is to determine the Rayleigh’s damping coefficients α and β and to evaluate the performance of the laminated rubber bearing using finite element and experimental modal analysis. Finding shows that, the finite element modal analysis with the addition of Rayleigh’s damping coefficients α and β, shows a good agreement with the experimental modal analysis in term of natural frequencies and mode shapes. Findings show that, the values of natural frequencies reduced when precise Rayleigh’s damping coefficient added in the finite element modal analysis. It can be concluded that both finite element and experimental modal analysis method can be used to estimate the accurate values of damping ratio and to determine the Rayleigh’s damping coefficients α and β as well.