Seismic Isolation System Research Articles

Analysis and design of non-linear seismic isolation systems for building structures—An overview

In this paper, the development of non-linear building isolation systems is overviewed. The study summarizes commonly used linear building isolation systems in two categories, which are building base isolation systems and building inter-storey isolation systems. Typical isolators including Lead-Rubber Bearings Friction Pendulum Bearings inter-storey viscous damper and Tuned Mass Damper are reviewed. The analysis and design of linear building isolation systems are also reported. After that, non-linear building isolation systems are introduced from two aspects based on their dynamic characteristics. They are (i) non-linear stiffness isolators including Quasi-Zero Stiffness isolators and Non-linear Energy Sink and (ii) non-linear damping isolators including power-law viscous dampers and magnetorheological dampers. Practical implementations of these non-linear isolators are introduced. Finally, the analysis and design of non-linear building isolation systems are discussed. Traditional equivalent linearization approaches and advanced non-linear frequency design approaches are introduced. The promising applications of the non-linear frequency design approaches to building isolation systems are also demonstrated in this review paper.

The seismic isolation system of Advanced Virgo Plus, Phase II

In 2025, the Advanced Virgo Plus (AdV+) gravitational-wave detector will enter Phase II, a thermal noise reduction upgrade involving the increase of the terminal mirror masses from 42 kg to 104 kg. This requires a revision of the SuperAttenuator (SA), the main attenuation system in AdV+, currently capable of reducing seismic noise by more than ten orders of magnitude in all six degrees of freedom above a few Hz. We briefly report the multiple updates of SA parts that have been planned to keep performance unchanged. As part of the study, simulations and/or design of upgraded elastic (maraging blades) and counter-elastic (magnetic antisprings) components were carried out, leading to a revision plan of all the filters in terminal SAs and notably of Filter 7 (F7), the lowest one. Prototyping and tests of the upgraded F7 and blades are underway at this time to validate the outputs of the study.

Анализ основных подходов к математическому моделированию системы «сооружение–сейсмоизоляция»

The article is devoted to the analysis of existing modern methods of seismic suppression and seismic isolation, as well as the issues of mathematical modeling of seismic isolation of objects using different seismic isolators according to the principle of operation. The article is divided into two sections. The first section provides a classification of active seismic isolation systems, as well as a brief overview of the principles of their operation and the main manufacturers of seismic isolation systems. In the second section, various approaches to the mathematical modeling of the «structure — seismic isolation» system are considered. There are analyzed and structured currently used schematic diagrams of various seismic isolation systems and seismic supports included in these systems.

Soil-structure interaction in a base and mid-story seismically isolated building

The main goal of this study is to analyze the performance of seismic isolation systems by implementing isolation to the base and inter-story of the buildings together, in order to reduce the earthquake impact in multi-story buildings. In addition the soil-structure interaction for these cases are taken into consideration. An example building model was composed to observe the effect of base isolation and mid-story isolation numerically. Analyses were performed by using SAP2000 software. A five story building was used as an example structure. Investigations were carried out for six different combinations that are: fixed base buildings, buildings with soil-structure interaction, buildings incorporating single base isolation system with and without consideration of soil-structure interaction, buildings with base and mid story isolation system with and without consideration of soil-structure interaction. Two different earthquake motions were selected for time-history analysis. The results obtained from time-history analysis were discussed comparatively, for all the base-isolation cases including and excluding soil-structure interaction. It has been concluded that the seismic isolation application of the base and mid-story improves the seismic performance of the building. In addition, it has been observed that the soil-structure interaction affects the building seismic performances according to the reference ground type.

Experimental Validation of Fast Design Rules for Curved Surface Slider Devices through the Hybrid Simulation Technique

In this work fast design procedures for a get-started definition of the seismic isolation system for buildings have been validated through the analysis of the outcomes of experimental hybrid tests. More specifically, earthquake simulations have been performed, by adopting both numerical and physical substructures, represented by an equivalent Multi Degree of Freedom for the building and a full-scale Double Curved Surface Slider isolator for the whole isolation system. A suite of seven natural seismic events has been selected, by ensuring the proper spectrum compatibility with respect to the hazard of the considered case study structure, in terms of acceleration response spectrum. Special attention has been focused on global results of the isolation layer, in terms of displacement and total force responses, together with the evaluation of the effective protection of the superstructure against eventual plastic deformation demands. The response parameters returned by both the single-events and as average values among the suite of selected events have been compared to the performance initially estimated through fast design rules. Furthermore, Non-Linear Time History Analyses have been performed, by adopting the same analytical model of the building used within the hybrid tests algorithm, for sake of comparison between numerical and experimental simulations.

Experimental study of passive seismic vibration isolation by trench-type periodic barrier

Seismic isolation systems protect structures and act as decoupling systems with the structure, which aims to uncouple the motion of the structure from incoming waves by reducing the kinetic energy of vibration transferred to structures. This research aims to study a non-invasive vibration isolation system using periodic barriers. A comprehensive field test program is completed to evaluate the wave isolation performance of empty trench and periodic barriers. The precast one-dimensional (1D) periodic barriers are arranged to form one long barrier and one short thick barrier to examine the influence of barrier length and the number of unit cells on the vibration isolation performance. The test program reported in this study is the P0 case (without periodic foundation), which serves as a reference group compared to previous test case P1 (with periodic barrier and reinforced concrete foundation) and test case P2 (with a combination of periodic barrier and periodic foundation). The triaxial (T-Rex) shaker truck generates excitation in three axis and the wave form include sine wave, sweep frequency and seismic waves. Each geophone sensor position records the triaxial soil response. The responses of soil along the direction of wave transfer, the normalized responses, and the frequency response function (FRF) are all provided and discussed. Various excitation inputs are comparable. It is found that the excitation directions influence the periodic barrier's effectiveness because of the dominant waveform. When FRF is compared between benchmark case and test cases, the periodic barriers’ screening effectiveness can be determined in the attenuation zones. These attenuation zones are expected to be the frequency band gaps of the periodic barrier. When the incoming wave frequency falls in this frequency band gap, the periodic barrier can isolate the vibration propagating towards the protected region.

Research on seismic performance of new bridge pier seismic reduction isolation system based on shaking table test

In view of the current poor seismic performance of bridges, this paper started with the vibration isolation and reduction mechanism of the bearing, and deduced the coordination relationship between the stress and the deformation of the bearing under the vibration isolation and vibration reduction working conditions. Combined with the shaking table test, the defect that the traditional rubber bearing has poor seismic isolation effect was analyzed. Based on this, a base-bearing double reduction system was proposed and its vibration reduction and isolation effect was compared with the traditional bearing. The shaking table test results showed that, compared with the traditional bearing, the proposed vibration reduction system had better energy dissipation effect and could weaken the apparent cracking damage of the pier under the action of earthquake. Under the 125 m/s2-750 m/s2 peak acceleration excitation of the EI-Centro wave, the proposed vibration reduction system could greatly reduce the displacement variation of the upper main beam by 20 %-47 %. Moreover, the results of dynamic amplification factor measured at the corresponding height of the two types of piers also verified that the proposed base-bearing double vibration reduction system had greater competitiveness when the peak acceleration of seismic waves was less than 500 m/s2.

A vertical inertial sensor with interferometric readout

High precision interferometers such as gravitational-wave detectors require complex seismic isolation systems in order to decouple the experiment from unwanted ground motion. Improved inertial sensors for active isolation potentially enhance the sensitivity of existing and future gravitational-wave detectors, especially below 30 Hz, and thereby increase the range of detectable astrophysical signals. This paper presents a vertical inertial sensor which senses the relative motion between an inertial test mass suspended by a blade spring and a seismically isolated platform. An interferometric readout was used which introduces low sensing noise, and preserves a large dynamic range due to fringe-counting. The expected sensitivity is comparable to other state-of-the-art interferometric inertial sensors and reaches values of at 100 mHz and at 1 Hz. The potential sensitivity improvement compared to commercial L-4C geophones is shown to be about two orders of magnitude at 10 mHz and 100 mHz and one order of magnitude at 1 Hz. The noise performance is expected to be limited by thermal noise of the inertial test mass suspension below 10 Hz. Further performance limitations of the sensor, such as tilt-to-vertical coupling from a non-perfect levelling of the test mass and nonlinearities in the interferometric readout, are also quantified and discussed.

A STUDY ON STATIC MECHANICAL PROPERTIES OF VERTICAL SEISMIC ISOLATION SYSTEM WITH PARALLEL LINK MECHANISM

This paper discusses the basic mechanical properties of a newly proposed parallel link mechanism as a three-dimensional seismic isolation system capable of supporting large loads. Specifically, the static restoring force characteristics of the entire mechanism, the moment caused by the spring force, and the inclination of the top surface due to 3-dimensional displacement were analyzed. The results show that stable static restoring force can be obtained by setting the initial angle within a certain range and using multiple units with a separation distance of 4 m or more between mechanisms.

Overturning effects on seismic performance of the hybrid friction-based seismic isolation system

The safety and reliability of the double-deck variable-depth composite truss bridge (DDVD-CTB) during earthquakes can be ensured by a hybrid friction-based seismic isolation system (HFBSIS). However, the overturning effects on seismic performance of HFBSIS is a significant concern, as it can induce vertical actions of isolation bearings. In this study, a single-degree-of-freedom (SDOF) system was first employed to describe the isolation system with the consideration of overturning effects. Following the nondimensionalization of motion equation, it indicated that the ratio of total axial load variations of spherical bearings to deadweight of the girder (γ) was a good indicator for the overturning effects on seismic performance. Then, the finite element (FE) model of SDOF system was developed and verified by the quasi-static cyclic test results. Finally, parametric sensitivity analyses were carried out to evaluate the degree of overturning effects on the seismic performance of the isolation system under different design parameters. Therefore, the maximum value γ of was less than 5 × 10−7 degree in the engineering practice. The nondimensionalization of motion equation considering overturning effects was approximately the same as that neglecting overturning effects, suggesting that overturning effects could be neglected when designing the HFBSIS in DDVD-CTB.

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.

Developing local rubber mixture for seismic base isolation system type high damping rubber bearing

The research objective is to develop a rubber mixture for the High Damping Rubber Bearing HDRB type of seismic base isolation system to resist seismic loads, and compare it with international companies’ brochures. Experiments were conducted on three HDRB models of 150 mm in diameter and 12 cm in height. These models were manufactured locally from natural rubber with other chemical additives and steel sheets. Load and unload tests (quasi-static) were conducted on the models simulating earthquake loads, first loaded with a vertical load of 110 kN, and then the base cyclic horizontally with an increasing amplitude of 25 % until 125 % of the shear strain. The vertical stiffness was 44,027 kN/m, the effective horizontal stiffness was 334 kN/m, and the damping ratio was 20.1 % experimentally. The results were within satisfactory ranges of the parametric values in the manufacturing design brochure, indicating the developed rubber mixture is convenient, giving a great motivation to manufacture seismic isolators locally at suitable prices.

Effect of modeling of inherent damping on the response and collapse performance of seismically isolated buildings

AbstractThis paper investigates the effect of inherent damping modeling on the computed seismic response and collapse performance of selected seismically isolated buildings. The analyzed seismically isolated buildings were designed by the procedures of the ASCE/SEI 7–16 standard. The structure is a six‐story perimeter frame building designed with special moment resisting frames or with special concentrically braced frames (SCBF) for a location in California. Three different seismic isolation systems are considered: (i) triple friction pendulum (TFP) bearings without moat walls, (ii) TFP bearings with moat walls (double concave [DC] friction pendulum bearings with moat walls have effectively the same ultimate behavior), and (iii) DC friction pendulum bearings without moat wall. The superstructure inherent damping schemes considered are (i) zero damping, (ii) modal damping, (iii) Zareian‐Medina damping, (iv) added virtual viscous dampers with and without force‐caps, and (v) added virtual viscous dampers with the same damping constant value. The response parameters computed are peak floor accelerations, peak story drift ratios, peak residual story drift ratios, peak isolator horizontal displacement, and floor acceleration spectra. Also, the probability of collapse in the maximum considered earthquake (MCER) is computed. It is shown that the modeling approach for the inherent damping has minor effects on the computed responses and the collapse probability of the studied seismically isolated buildings, except for the peak floor acceleration and the floor response spectra for periods below one second. It is suggested that a convenient way to model inherent damping is to use virtual viscous dampers with all having the same damping constant.

A generalized model of lead rubber bearing considering large strain stiffening and degradation

Lead rubber bearings (LRBs) have been widely used in seismic isolation systems to mitigate earthquake damage in regions characterized by high seismic intensity. However, effective isolation is achieved at the expense of largely concentrated displacement in the isolation layer. Past experimental studies have confirmed that rubber stiffening and degradation properties are essential for LRBs at large cyclic strains. That is, accurately simulating the complex nonlinear behavior of LRBs is significant to evaluate the performance of isolated structures under strong earthquakes. Nevertheless, most LRB models in engineering practice cannot capture the strong nonlinear properties and the existing models for elaborate modeling are not widely used due to the complicated shape parameters. For this reason, the present study proposes a generalized Bouc–Wen model that can reasonably reflect the large strain stiffening and strength degradation properties of rubber. The traditional Bouc–Wen model of LRBs was introduced first. Subsequently, a generalized Bouc–Wen model of LRBs that is capable of simulating the observed large cyclic behavior with reasonable accuracy was developed. The model was further verified by the experimental results of LRBs with different design parameters under various loading conditions. Moreover, time history analyses were conducted to evaluate the earthquake responses of the single-degree-of-freedom system with the traditional Bouc–Wen and generalized Bouc–Wen model. Comparison proves that the two bearing models can closely estimate the peak deformation and shear force in minor and moderate earthquakes. By contrast, the generalized model can accurately capture the LRB properties under large cyclic strain that can restrain the bearing deformation but possibly increase the shear force significantly under strong earthquakes.

Shake table test and numerical study on a capable and resilient lateral seismic isolation system for long-span cable-stayed bridges

Seismic isolation of long-span cable-stayed bridges in the transverse direction requires both large restoring force and large deformation capacity for the girder–tower connections, especially in critical seismic conditions, which challenges a lot for the design of earthquake resisting system (ERS). A capable and resilient lateral isolation system (CRLIS) is proposed that comprises FRP cables and a parallel FVD for the girder–tower connections and can provide the desired large restoring force and large deformation capacity. Based on a practical long-span cable-stayed bridge, detailed design parameters of the CRLIS were presented through a parameter analysis, and then a 1/35-scale physical model of the long-span cable-stayed bridge was made and tested on a four-shake-table testing system in the Multi-functional Shaking Table Lab at Tongji University. Details of the physical model including the scale factor, configuration of the structural members, additional mass blocks, boundary conditions, and the essential pretest numerical validation were briefly introduced. The experimental results show that the CRLIS could significantly reduce the acceleration response of the girder and the shear force to the girder–tower connections, as well as a considerable reduction of the forces to the towers. Numerical simulation is also conducted and validated by the experimental data; specifically, the sensitivity of the numerical simulation result to the Rayleigh damping matrix is investigated and a definition of the Rayleigh damping matrix is suggested. Furthermore, the isolation effectiveness of the CRLIS is concisely analyzed.

Geotechnical Seismic Isolation System Based on Rubber-Sand Mixtures for Rural Residence Buildings: Shaking Table Test

The anti-seismic problem of rural residential buildings is the weak link of seismic retrofitting in China. Recently, geotechnical seismic isolation (GSI) technology based on rubber-sand mixtures (GSI-RSM) using rubber-sand mixtures (RSM) between the structural foundation and the foundation soil has been proven to have the possibility of potential applications in rural residential buildings. Many theoretical studies exist on the effectiveness of seismic isolation of the GSI-RSM system, but few studies on either the seismic response test of model buildings placed on the RSM layer or the large-scale shaking table test exist. Therefore, this study considers a large shaking table test performed on a 1/4 single-story masonry structure model with and without a GSI-RSM system by selecting a standard input ground motion and varying input acceleration amplitudes. The test results show that the GSI-RSM system can reduce the seismic response of superstructures. The isolation effect of the GSI-RSM system is low in small earthquakes and increases with increasing earthquake magnitude. Overall, the RSM layer can filter part of the high-frequency components of the earthquake to transmit to the superstructure and consume more seismic energy by generating friction slip in the interaction with the structural foundation.

Dynamic behavior of geocell-reinforced rubber sand mixtures under cyclic simple shear loading

Due to the attributes of low shear modulus and high initial damping, rubber sand mixtures (RSM) can be used as a soil alternative to reduce ground motions when seismic loads are of great concern. However, when RSM is used as a vibration isolation material for geotechnical seismic isolation systems, it suffers from a lack of load-bearing capacity. To overcome this, a three-dimensional interconnected geocell (one type of geosynthetics) is placed within RSM to increase the vertical confinement of the system. In this technical note, to investigate the shear modulus and damping ratio of geocell-reinforced RSM, large-scale cyclic triaxial tests were conducted on specimens prepared with four granulated rubber contents (by weight) and sheared under different cyclic shear strain amplitudes. The results show that Geocell reinforcement can restrict the development of local shear bands in the specimen, weaken the anti-S-shaped characteristics of hysteresis loops and enhance the damping ratio of RSM at large strain amplitudes. The tuck net effect causes an increase in the normal stress of both contact particles, and then leads to the degradation rate of the maximum shear modulus of RSM varying with the rubber content and vertical pressure. The normalized shear modulus degradation curves show the influence range of geocell reinforcement, and demonstrate that a rubber content of 20% for reinforced specimen may be an optimal value from the perspective of the stability of dynamic properties. Additionally, the quantitative analysis of the effect of geocell reinforcement on the mechanical behavior of RSM can provide a reference for subsequent theoretical research and engineering applications.

Inspection and repair considerations for downtime assessment of seismically isolated buildings

This paper investigates the seismic downtime of seismically isolated buildings with steel moment or braced frames designed by the procedures of ASCE/SEI 7–16. The seismic isolation systems considered in this study are comprised of triple or double friction pendulum isolation bearings with and without moat walls. The seismic downtime is calculated from the damage to structural components and non-structural components, demolition and collapse of buildings. The downtime components (repair and inspection) are defined, and mathematical expressions are provided for the computation of downtime fragility curves, expected annual downtime, and economic losses due to the expected annual downtime. The procedure is then implemented using the results of nonlinear response history analysis from previous studies by the first author. The study demonstrates that the expected annual downtime of seismically isolated buildings is less than that of the comparable non-isolated buildings regardless of the seismic isolation systems used. Among the cases of seismically isolated buildings studied in this paper, it is found that the most effective structural system to mitigate long downtime is the seismically isolated building with seismic isolators with enhanced sizes and with braced frames that are designed to be minimally compliant with the seismic design requirements of ASCE/SEI 7–16.

Optimization of Seismic Base Isolation System Using a Fuzzy Reinforced Swarm Intelligence

The current study deals with the optimization of seismic isolation system parameters applied in base-isolated buildings. In this regard, to consider the more realistic condition, both near-fault and far-fault earthquake ground motions are taken into account by simultaneously imposing six different acceleration records during the direct time integration analysis of the structure. The minimization of the system's peak acceleration ratio is defined as the objective function of the optimization model. To get feasible results, the determining parameters of the isolator are restricted. Such that, while the isolation system period and damping ratio are kept within a predefined range, the maximum displacement of the system is monitored and limited during the optimization process. To solve the proposed optimization model, an enhanced version of the Deferential Evolution method so-called Fuzzy Differential Evolution incorporated Virtual Mutant (FDEVM) is employed. The FDEVM method applies a fuzzy decision-making mechanism to adopt its search behavior based on the governing conditions of the current problem. It also uses a new mutant vector called virtual mutant to contribute information of all population based on each agent's quality. So, the FDEVM works as a self-adaptive and parameter-free search algorithm. The acquired results show that the FDEVM works properly to find the optimal values for the dynamic parameters of the seismic base isolation system.

Experimental and finite element analyses of laterally loaded RC piles with pre-hole filled by various filling materials in IABs

Under seismic actions, reinforced concrete (RC) piles are considered the most vulnerable components of integral abutment bridges (IABs). This paper investigates the mechanical behavior of the pile with pre-hole seismic isolation system through pseudo-static low cycle tests and numerical analyses on scaled specimens with various filling materials. The ultimate goal of this technical solution is to improve the seismic performance of IABs. The experimental results proved that the pile specimens with pre-hole seismic isolation system exhibit higher energy dissipation than those without pre-hole. The equivalent viscous damping is 17.1 ∼ 49.3 % higher when the filling is rubber and 3 ∼ 12 % higher using foam. The influence of the pre-hole diameter and soil deformation is also significant. When the pre-hole diameter is large enough, the horizontal displacement of the pile specimen is entirely absorbed by the rubber particles. Nevertheless, the pre-hole seismic isolation system does not significantly influence the failure mode, skeleton curve, yield load and bearing capacity. Finite element models (FEMs) were implemented in ABAQUS and calibrated using the experimental results. The FEMs allowed extrapolating the experimental outcomes under different geometrical and mechanical configurations, considering the sand-pile interaction with various filling materials (rubber particles and foam), and pre-hole sizes. The numerical results showed that the subgrade modulus and the ultimate soil resistance decrease when the pile has a pre-hole seismic isolation system. Therefore, the lateral deformation of a pile with pre-hole seismic isolation system can be estimated by multiplying the subgrade modulus used for the pile by a specific reduction factor dependent on the pre-hole geometry and the mechanical parameters of the filling material. The paper proposes and discusses a novel definition of the p-y curves for predicting the response of the pile with pre-hole seismic isolation system modified from classical p-y curves.