Seismic Isolation Bearings Research Articles

Experimental and numerical assessment of grout-filled tennis balls as seismic isolation bearings

This paper describes the behavior of a low-cost seismic isolator comprising a grout-filled tennis ball rolling on concrete plates. The isolator could be used for isolating lightweight structures. Initially, the axial response of the system was characterized. Subsequently, full-scale isolators were tested in combined compression and lateral cyclic loading. Parameters of investigation were the testing velocity (frequency), the bearing load, the degradation due to consecutive loading, the bearing temperature, the specimen-to-specimen variability, and the engagement of the displacement restrainer. Finally, a three-dimensional finite element model was developed to model in detail the response of the isolator and to explore the influence of the rubber thickness. This is the first study to characterize the above effects and to propose a finite element model of these isolators. Results showed that the lateral cyclic response of the isolators is bilinear and can be approximated by rigid-body equations, whereas the values of the rolling friction coefficient and the yield displacement are suitable for seismic isolation applications. The specimen-to-specimen variability was minimal. Unlike sliding isolation systems, an increased bearing compressive load leads to a higher rolling friction coefficient. Analytical equations are offered to describe this effect. The rolling friction coefficient does not depend on velocity (frequency) or temperature, and the isolators did not deteriorate under consecutive loading. The proposed displacement restrainer effectively limits the motion of the isolator. The developed finite element model accurately captures the experimental response. It was used to study the influence of the thickness of the rubber layer on the lateral response, to conclude that it is minimal, for rubber layers ranging from 3.4 to 7 mm.

Optimization of Mechanical Performance of Seismic Isolation Bearings for Continuous Beam Bridges

Optimization of Mechanical Performance of Seismic Isolation Bearings for Continuous Beam Bridges

Study on the seismic mitigation effects of inerter isolated storage tanks

Liquefied Natural Gas (LNG) storage tanks can ensure national energy sufficiency, but they are vulnerable to earthquakes. Although ordinary seismic isolation bearings can effectively reduce the base shear force and overturning moment, they tend to amplify the height of the sloshing wave. In this paper, a hybrid vibration control method for LNG storage tanks is proposed, paralleling the series viscous mass damper (SVMD) devices with Lead-core rubber bearings (LRB). The seismic mitigation effects of this parallel seismic isolation scheme were investigated. First, three-dimensional finite element models of fixed base, LRB isolated and SVMD isolated tanks were established, and nonlinear time history analyses were performed for the three types of tanks to compare the seismic responses. It was concluded that SVMD can effectively control the sloshing wave height. In addition, the effects of site types, storage liquid heights, and SVMD's performance parameters on the seismic mitigation effects were also studied. It was found that the softer the site soil, the higher the storage liquid height would make seismic isolation less efficient. The increase of SVMD's additional equivalent mass reduces the sloshing wave height, increases the shear-to-weight ratio, and has little influence on the base displacement. The increase of SVMD's additional equivalent damping reduces the sloshing wave height, base shear force, and base displacement of the tank. The final conclusion is that SVMD can effectively control the sloshing wave height and has a good seismic mitigation effect.

Application of Seismic Isolation Bearings in Aqueducts

Application of Seismic Isolation Bearings in Aqueducts

Research on the Seismic Isolation Effect of the Ring Spring–Friction Pendulum Bearing in the Dakai Underground Subway Station

During strong earthquakes, the vertical seismic force becomes an essential factor affecting shallow underground structures that cannot be ignored. In this situation, it is proposed that ring spring–friction pendulum two-way seismic isolation bearings be set up at the bottom of such structures. Targeting the Dakai underground station and the Kobe earthquake, a soil-structure force model was established based on the damage to the underground structure and dynamic simulation was carried out using Abaqus software. The advantages of the ring spring–friction pendulum bearing over the ring spring bearing alone and the friction pendulum bearing alone were compared. The simulation results showed that the structure displayed a good seismic isolation effect in both horizontal and vertical directions after setting the ring spring–friction pendulum bearing. The deflection in the midspan of the roof reduced to less than 5 cm, the horizontal relative displacement of the structure reduced to less than 3 cm, there was no obvious damage to the structure, the axial pressure ratio of the mid-pillar reduced to less than 0.5, the axial force on the mid-pillar reduced by more than 50%, and the shear force reduced by more than 30%. In addition, by comparing the damage to the structure after setting the annular spring bearing and the friction pendulum bearing, we found that a vertical seismic isolation device is more crucial than a horizontal seismic isolation device for shallow underground structures. Setting a vertical damping device can make the structure retain part of the ductility and reduce the damage to the structure, so the ground vertical seismic mitigation design should be strengthened when a shallow underground structure is designed.

Numerical Analysis of Elastomeric Bearings Equipped with Steel Ring Restrainers

In order to improve the seismic performance of bridges, the design of high-performance isolation bearings can effectively reduce the displacement response caused by earthquakes. This paper proposes a novel seismic isolation bearing (EB-SRRs) to prevent the unseating of bridges. Based on the finite element (FE) analysis method, the mechanical properties of EBSRR are simulated and analyzed, and the performance of EB is compared experimentally. The experimental results show:(1) When the shear strain reaches 93%, the reaction force provided by EB SRRs model is gradually higher than that of EB model due to the activation of SRRs; (2)With the continuous increase of horizontal displacement, the reaction force of EBSRR model increases significantly; (3)SRR increases the area of hysteresis loop, and the increased area in each loop increases with the increase of load displacement

A high-sensitivity rotatable 3D displacement sensor

Aiming at the problems of low sensitivity and low accuracy caused by the displacement transfer mechanism of three displacement sensors used simultaneously in the 3D displacement monitoring of seismic isolation bearings, the paper has proposed a high-sensitivity rotatable 3D displacement sensor. The sensor adds through holes on the surface of the equal-strength cantilever beam to form a cross beam, which increases the bending strain on the beam surface to improve the sensitivity. By adding a gyroscope and a mechanical rotation structure, a single sensor can measure the 3D displacement at the same time, reducing the adverse effects displacement transmission mechanism on the accuracy of the measurement. ANSYS software was used to simulate and optimize the parameters of the size of through-hole of the sensor beam to determine the appropriate size and location of the through-hole. Finally, the sensor was developed and its static characteristics and displacement measurement performance in static and dynamic 3D space were tested based on the simulation results. The test results have shown that the sensor has a sensitivity of 16.29 mV/mm and an accuracy of 0.9% in the range of 0–160 mm. Its static and dynamic 3D spatial displacement measurement errors are less than 2 mm, which can meet the accuracy requirements of 3D displacement measurement and sensitivity for structural health monitoring of seismic isolation bearings.

Base‐isolation design of shear wall structures using physics‐rule‐co‐guided self‐supervised generative adversarial networks

AbstractSeismic isolation can significantly improve the seismic resilience of buildings, resulting in a growing demand for seismic isolation designs. Meanwhile, the deep generative network‐based intelligent design can significantly increase scheme design efficiency. However, the performance of existing intelligent scheme designs is constrained by data quality and quantity. The limited availability of isolation design data hinders the development of intelligent seismic isolation design. Therefore, there is an emerging demand to establish an intelligent scheme design method that is free from data constraints and that can learn the physical mechanism and design rules. Consequently, this study proposes a physics‐rule‐co‐guided self‐supervised generative adversarial network (GAN) that can generate the layout and parameters of seismic isolation bearings by inputting the layout drawings of the shear wall structures. The critical physics‐rule‐co‐guided network model consists of a physics estimator, rule evaluator, discriminator, and design generator. The physics estimator is a deep neural network‐based surrogate model for predicting the mechanical response of an isolated structure, whereas the rule evaluator is a tensor operation‐based loss calculator that considers design rules. Furthermore, the proposed GAN model masters the schematic design ability of the seismic isolation of shear wall structures through multiphase hybrid learning of the pseudo‐labels, physical mechanism, and isolation design rules, obviating the need for ground‐truth data. Case studies also prove the rationality of the method, where the design results can effectively meet the code requirements and reduce the seismic response of the structure.

Shaking table test study of nuclear power plant model considering soil-structure interaction effect

The influence analysis of site condition is fundamental to the seismic design of nuclear power plants. In this paper, a series of shaking table tests were performed to investigate the Soil-Structure Interaction (SSI) effect on the seismic response of nuclear power structures. An AP1000 nuclear power plant was taken as the objective structure, lead rubber bearings (LRBs) were used as the isolators and Shanghai silty clay was selected as the model soil. Test results show that (1) The soil has different effects on the dynamic characteristics of isolated and non-isolated model structures. (2) During the shaking table test, the foundation edge is subject to the highest soil pressure, and a contact surface separation between the foundation and the soil begins to occur under the seismic-margin earthquake (SME) seismic input level. (3) Both for the rigid and soil foundation, seismic isolation bearings can effectively reduce the acceleration response of the superstructure. (4) For the non-isolated model, the SSI effect significantly amplifies the seismic response at the bottom floor of the structure in the low frequency range, and an obvious rocking behavior occurs at the operating basis earthquake (OBE) seismic input level. (5) For the isolated model, the SSI effect reduces the hysteresis capacity of the seismic isolation system and amplifies the seismic response at the bottom floor, especially in the vertical direction. The site condition and the use of an isolation system have a significant impact on the seismic response of a nuclear power structure. Therefore, in the design and safety assessment of nuclear power plants, the influences of soil characteristics and isolation equipment in the soil-structure interaction system should be fully considered.

Seismic performance improvement of continuous rigid-frame bridges with hybrid control system under near-fault ground motions

To improve the seismic performance of continuous rigid-frame bridges (CRFBs) in near-fault earthquakes, this study developed a hybrid seismic control system (HSCS) combining a three-dimensional hybrid seismic isolation bearing (3D-HSIB) with a longitudinal fluid viscous damper (L-FVD). The hybrid numerical model of the HSCS and the nonlinear numerical model of a CRFB prototype were simulated in OpenSees. The study comparatively analyzed the seismic responses of non-controlled bridges and HSCS-controlled bridges under near-fault ground motions, evaluated the seismic control effectiveness of the HSCS, and investigated the effects of vertical excitations on the seismic performance of the CRFB. The numerical results show that the proposed HSCS effectively reduces the three-directional seismic responses of the CRFB. When the PGA is 0.4 g, the seismic isolation ratios of displacement, internal force, and pounding force all exceed 0.4. The hysteresis behavior of the HSCS can be fully utilized under three-directional excitations with pulse-like effects. The girder-end uplift behavior under vertical excitation can be effectively controlled by the proposed 3D-HSIB with a seismic isolation ratio of at least 0.6. When vertical excitation exceeds a certain level, the bearing is tensioned upward while axial tension force may also occur in main piers. Furthermore, the seismic responses under pulse-like near-fault ground motions are significantly larger than those under non-pulse near-fault ground motions. This work may provide a useful reference for the seismic analysis and design of CRFBs.

Seismic Responses of Aqueducts Using a New Type of Self-Centering Seismic Isolation Bearing

An aqueduct is a bridge-like structure that supports a canal passing over a river or low ground, and it is an important part of a water conveyance system. Aqueduct piers are extremely vulnerable to damage during strong earthquakes that can result in structural collapse. Further, excessive seismic displacement will also fracture an aqueduct’s rubber water-stop and interrupt the normal service of an aqueduct after an earthquake. Therefore, improving the seismic capacity and post-earthquake resilience of aqueducts is of great importance. In this paper, a new type of self-centering seismic isolation bearing, the inclined plane guide bearing (IPGB), is proposed for the seismic design of aqueducts, and it is studied both experimentally and numerically. Firstly, a typical aqueduct project and the setting of the IPGBs are introduced. Then, the test design, test cases, and test results of shaking table tests for two different pier-height aqueducts are presented. The seismic responses of the two models are studied, and the results show that the aqueduct that used IPGBs has a smaller bearing displacement and better post-earthquake resilience. Finally, a numerical simulation method applicable to aqueducts using IPGBs is proposed, and its accuracy is verified by comparing the results of the numerical simulation and the shaking table test.

Annular fiber-reinforced elastomeric bearings for seismic isolation of lightweight structures

The conventional laminated elastomeric bearing isolators, as a mature technology, have found significant application in earthquake protection of civil structures, which are typically large in size, heavy, and expensive in cost. The technology is not as effective in the seismic isolation of lightweight structures due to the challenges in providing effective period-shift while accommodating large isolator displacement demands. Further horizontal flexibility may yet be required in the elastomeric isolators concerning the Seismic isolation of lightweight structures. A novel hollow circular (HC, also called the annular) type of fiber-reinforced elastomeric isolators (FREIs) is introduced and examined in this study. To demonstrate the validity of the concept, the dynamic response characteristics of two similar full-scale HC-FREIs were evaluated experimentally and compared with those of a corresponding solid circular (SC)-FREI as the control specimen. The response parameters, performance limit states, and failure modes of the two isolator types were evaluated and compared in detail. In addition, the performance of the two isolator types in the base isolation of a lightweight structure was investigated. Given the significantly increased horizontal flexibility and superior damping properties, the unbonded HC-FREIs offer a feasible solution for the effective earthquake mitigation of many lightweight structures. Additionally, the comparatively lower volume of materials and the lighter weight of the isolator provide economic advantages for HC-FREIs over their SC-FREI counterparts.

Design methodology and modified shear constitutive model of the shear pin connection

Currently, the shear pin connection (SPC) is a structural measure in the double spherical seismic isolation bearing (DSSIB). However, there is no unified design methodology for the SPC. In addition, the existing shear constitutive model is the linear elastic model (LEM). Its drawback is the inability to capture the gap in the bearing and the plasticity, damage, as well as fracture behavior of the SPC. Therefore, based on the performance requirements for two-level seismic fortification, a detailed design methodology for the SPC is proposed. With the SPC in the Fuzhou Daoqingzhou Bridge as a prototype, the finite element model of the SPC is developed in order to discuss the applicability of the LEM for predicating the shear behavior of SPC. The results showed that the fracture displacement and absorbed energy obtained by the finite element analysis were significantly larger than those predicted by the LEM. Then, to compensate the drawback of the LEM, a tri-linear model (TLM) is proposed as the modified shear constitutive model of the SPC. Finally, the effects of TLM and LEM of the SPC on seismic performance of the isolated bridge were investigated. Obviously, the maximum displacement of the bearing calculated by the TLM is up to 1.38 times that calculated by the LEM. This suggests that the TLM has accurate predictions of mechanical property of the SPC.

Experimental and Numerical Investigation for Seismic Performance of a Large-Scale LNG Storage Tank Structure Model

As special equipment for storing energy, the safety performance of liquified natural gas (LNG) storage tanks under earthquake action is extremely important. To study the dynamic characteristics of the large-scale LNG storage tank structure and the dynamic response under earthquake action, the shaking table test and numerical simulation analysis of the LNG storage tank structure model are carried out. The results of the shaking table test demonstrate that the natural vibration frequency of the tank model is significantly reduced after the isolation measures are taken. The acceleration response of the seismic storage tank increases approximately linearly along the direction of height, and the seismic isolation bearing has a significant seismic isolation effect on the acceleration of the storage tank. The numerical simulation results show that the seismic responses and their spectral characteristic curves of the numerical model and the shaking table test are the same, which verifies the feasibility and rationality of the numerical model. After seismic isolation measures are taken, the seismic responses of large-scale LNG storage tanks, such as base shear force, overturning bending moment and acceleration, are reduced to varying degrees, but the displacement of the storage tank increases to some extent. When carrying out the seismic isolation design of LNG storage tanks, it is necessary to focus on the displacement of the storage tank to prevent damage of the auxiliary pipeline led by excessive displacement.

Pounding performance between a seismic-isolated long-span girder bridge and its approaches

For girder bridges located in regions with a high seismic hazard level, seismic isolation bearings are usually implemented to suppress the seismic inertial force transmitted from the superstructure to substructures, protecting the pier columns and foundations. However, whether potential pounding might happen for these seismic-isolated girder bridges between adjacent units are scarcely considered, especially for those with long spans where the wave passage effect is of great significance. This paper develops a finite element model for a typical hybrid truss-girder bridge, based on which the influence of seismic isolation bearings and wave passage effect on pounding is carefully investigated considering both near-fault and far-field motions. The results show that for this type of long-span girder bridges, pounding may happen even the adjacent bridge units are designed with similar vibration periods, especially when near-fault motions and wave passage effect are considered. Under non-uniform excitations with different apparent wave velocities, the employment of isolation bearings can reduce the relative displacement at expansion joints and thus improve the performance against pounding; however, the occurrence of pounding and damage of expansion joints cannot be fully avoided. Further, motions with lower apparent velocities generally correspond to more devastating responses, which should be particularly considered during engineering practice.

Seismic Analysis of Reticulated Shell Structure Based on Sensor Network for Smart Transportation Seismic Isolation Bearings

Earthquakes are one of the most frequent and inevitable natural disasters that occur on Earth. The most important seismic isolation device used in the isolation technology is the isolation bearing, but the limited structure of the isolation bearing is not suitable for the seismic isolation and shock absorption of smart transportation buildings. Therefore, it is very important to improve the new generation of seismic isolation structures with good seismic isolation effect, stable performance, and economical performance. It is very important to study the structural composition of the isolation bearing and the rigidity of the isolation structure. Isolation bearings are designed to resist and absorb the energy of seismic shocks by installing substructures in the structure. Active control involves installing sensors on the structure and its foundation to determine how the structure responds to seismic action. In this paper, based on the intelligent transportation of the sensor network, the reticulated shell structure of the isolation bearing is analyzed. By introducing the architecture and network layout of the sensor network, it is beneficial to obtain more accurate seismic data in complex and difficult terrain. This paper analyzes the technical principle of seismic isolation technology, which can effectively avoid the upward transmission of ground vibration by increasing the flexibility and proper damping of the system. From the experimental data of the seismic response of the ground-isolated structure to the near-field pulsation and far-field vibration, the total energy of the ground-isolated structure under the near-field pulsed ground motion is the largest. The seismic isolation effect of the reticulated shell structure of the seismic isolation bearing prevents more than 80% of the seismic energy from being transmitted to the superstructure.

Seismic performance assessment of base-isolated tall pier bridges using friction pendulum bearings achieving resilient design

Traditional seismic isolation bearings, which are widely adopted in conventional bridges between superstructures (girders) and piers, are not effective for tall pier ones, due to the considerable distributed mass and corresponding seismic inertial force of columns. To address this issue, applying isolators at the base of pier columns appears to be a promising approach mitigating seismic demands of tall pier bridges. This paper investigated the feasibility and efficiency of base isolation by implementing friction pendulum bearings (FPBs) at the bottom of tall piers. The seismic performance of the FPB-isolated bridge system was evaluated through nonlinear time history analysis and compared with its counterparts using fixed base. The results showed that with the employment of FPBs, the tall pier columns would remain elastic during strong earthquake excitations, and the displacement demands of FPBs were less than 40% of the pre-determined capacity. Through parametric analysis, a greater value of radius (R) of concave surface was recommended for designing FPBs; while the friction coefficient (μ) should be careful determined to achieve balance between seismic displacement and force demands.

Optimal Selection of Earthquake Resisting Schemes for Jakarta‐Bandung High‐Speed Railway

The Jakarta‐Bandung high‐speed railway is the first overseas project involving China’s high‐speed railway. Owing to the high seismic intensity in this area, the optimal selection of earthquake resisting schemes is critical for short‐span bridges, and such schemes are related to the safety and cost‐effectiveness of the entire line. This study compares the safety and cost‐effectiveness of four earthquake resisting schemes: (i) prestressed concrete (PC) simply‐supported box beams using common spherical steel bearings; (ii) PC simply‐supported box beams using seismic isolation bearings; (iii) steel‐concrete (SC) composite simply‐supported beams using seismic isolation bearings; (iv) reinforced concrete (RC) rigid frames. The results indicate that PC beams using more expensive seismic isolation bearings reduce the cost of the substructure, making it more cost‐effective. In contrast, the scheme of SC composite beams is the most expensive one, and the associated maintenance costs are also the highest. Although the scheme of RC rigid frames is the cheapest among the evaluated schemes, it is only suitable for relatively stiff sites with low pier heights. Overall, PC beams with isolation bearings exhibit good seismic performance and are suitable for prefabricated construction; therefore, this scheme can be applied in various soil conditions with relatively low costs, and it is recommended for use throughout the entire Jakarta‐Bandung high‐speed railway.

Modelling lead-rubber seismic isolation bearings using the unified mechanics theory

Lead-rubber seismic isolation bearings (LRB) have been installed in a number of essential and critical structures, like hospitals, universities and bridges, in order to provide them with period lengthening and the capacity of dissipating a considerable amount of energy to mitigate the effects of strong ground motions. Therefore, studying the damage mechanics of this kind of devices is fundamental to understand and accurately describe their thermo-mechanical behavior, so that seismically isolated structures can be designed more safely. Hitherto, the hysteretic behavior of LRB has been modeled using 1) Newtonian mechanics and empirical curve fitting degradation functions, or 2) heat conduction theories and idealized bilinear curves which include degradation effects. The reason for using models that are essentially phenomenological or that contain some adjusted parameters is the fact that Newton’s universal laws of motion lack the term to account for degradation and energy loss of a system. In this paper, the Unified Mechanics Theory – which integrates laws of Thermodynamics and Newtonian mechanics – is used to model the force-displacement response of LRB. Indeed, there is no need for curve fitting techniques to describe their damage behavior because degradation is calculated at every point using entropy generation along the Thermodynamics State Index (TSI) axis. A finite element model of a lead-rubber bearing was constructed in ABAQUS, where a user material subroutine UMAT was implemented to define the Unified Mechanics Theory equations and the viscoplastic constitutive model for lead. Finite element analysis results were compared with experimental test data.

Experimental Approach for the Failure Mode of Small Laminated Rubber Bearings for Seismic Isolation of Nuclear Components

Response characteristics of small-sized laminated rubber bearings (LRBs) with partial damage and total failure were investigated. For nuclear component seismic isolation, ultimate response characteristics are mainly reviewed using a beyond design basis earthquake (BDBE). Static tests, 3D shaking table tests, and verification analyses were performed using optional LRB design prototypes. During the static test, the hysteresis curve behavior from buckling to potential damage was observed by applying excessive shear deformation. The damaged rubber surface of the laminated section inside the LRB was checked through water jet cutting. A stress review by response spectrum analysis was performed to simulate the dynamic tests and predict seismic inputs’ intensity level that triggers LRB damage. Shaking table tests were executed to determine seismic response characteristics with partial damage and to confirm the stability of the superstructure when the supporting LRBs completely fail. Shear buckling in LRBs by high levels of BDBE may be quickly initiated via partial damage or total failure by the addition of torsional or rotational behavior caused by a change in the dynamic characteristics. Furthermore, the maximum seismic displacement can be limited within the range of the design interface due to the successive slip behavior, even during total LRB failure.