Seismic Isolation System Research Articles

Mechanical Behaviors and Numerical Simulation Analysis of a New Isolation System

Finite element analysis is one of the key steps in evaluating the effectiveness of an isolation system. The aim of this paper is to research the mechanical properties of sliding and rolling friction systems and their application for isolating frame structures. A hybrid seismic isolation system is proposed, which aims to protect the superstructure by reducing dynamic response. The effect of different parameters on the friction coefficient of the isolation bearing was tested using a compression-shear testing machine, and the results showed that various parameters significantly affected the friction coefficient. In addition, a numerical analysis finite element model was established using SAP2000 software to compare the seismic isolation performance of the hybrid isolation system with that of traditional seismic-resistant structures. The results showed that the composite isolation system not only effectively reduced inter-story shear and acceleration, but also slightly enhanced the seismic isolation effect as the friction coefficient decreased.

Seismic fragility analysis of bridge-isolator-foundation-soil systems in subfreezing temperatures

Several cold regions around the world are in seismic active zones. Seasonal freezing can significantly affect the seismic performance of complex bridge-isolator-foundation-soil systems by inducing brittle failure and premature collapse due to a combination of load reversals and cold temperature behavior of the bridge material. In cold conditions, constitutive material of bridge components, namely, concrete, steel reinforcement, rubber, and supporting soil undergo substantial stiffening which afflicts the ductility capacity of bridges. This study investigates the seismic performance of four bridge cases, namely, isolated bridge supported by pile groups, monolithic bridge supported by pile groups, isolated fixed-base bridge, and monolithic fixed-base bridge at room and subfreezing temperatures to unmask the effectiveness of using Fiber Reinforced Elastomeric Isolator (FREI) as a retrofit measure and to evaluate the performance of bridges at temperatures ranging from room (i.e. 20 °C) to −37 °C. To this end, an analysis matrix is developed based on the climatic condition of the bridge site along with the code provisions. A seismic fragility analysis is carried out in the context of Incremental Dynamic Analysis (IDA) using a set of synthetic ground motion records for longitudinal and transverse directions of the bridge, independently. It is shown that while the seismic isolation system can effectively mitigate the probability of damage to the bridge at room temperatures, isolated bridges demonstrated an acceptable behavior at subfreezing temperatures.

To Investigate Different Parameters of Economic Sliding Based Seismic Isolation System

ABSTRACT Masonry structures are frequently constructed in developing countries because of their affordability and ease of construction, even though they are vulnerable and perform poorly during earthquakes. Experimental and numerical studies were carried out to determine the optimum thickness of the isolation layer for a recently developed, low-cost seismic isolation system known as the Reinforced-Cut-Wall (RCW). The parameters of the isolation layer were optimized during the experimental and numerical investigations using hollow concrete blocks. Quasi-static cyclic tests were performed on a 1:3 reduced-scale brick masonry wall incorporating the RCW isolation scheme, validating the better performance of the proposed isolation technique.

Impedance‐matching model‐in‐the‐loop simulation

AbstractImpedance matching is a novel approach to executing model‐in‐the‐loop (MIL) simulations. The concept, key features, and sample applications of this approach have been described in a series of publications. This paper advances theory and implementation for impedance‐matching MIL by: (1) developing a feedback linearization technique for implementing MIL for nonlinear virtual systems, (2) systematically characterizing MIL performance‐stability tradeoffs using three design‐oriented criteria—performance: defined as closeness of the controlled‐actuator impedance to the virtual‐boundary impedance; control effort: low controller response at high frequencies to reduce sensitivity to measurement noise and uncertainties in the actuator model; and stability: pursued using passivity of the controlled actuator system, and (3) assessing, through experimentation, the robustness of two ways to estimate feedback reaction force from the test article. These fundamental advancements to MIL are described using a one‐dimensional configuration consisting of a fluid‐filled cylindrical vessel as the physical test article and a uniaxial hydraulic shake table controlled to imitate different seismic isolation systems at the base of the vessel.

Probabilistic Incremental Dynamic Analysis for Seismic Isolation Systems through Integration with the NHERI-SimCenter Performance-Based Engineering Application

In the wake of the 1994 Northridge and 1995 Kobe earthquakes, structural designers adopted performance-based engineering concepts instead of traditional deterministic design approaches. The primary change was to evaluate the design according to stakeholders’ interests instead of the engineering parameters. This evaluation process required a probabilistic estimation for the included variables at all design stages. The NHERI-SimCenter application framework provides generic solutions implemented in different hazard simulation problems. Seismic isolation is an efficient, proven technique for improving seismic performance by limiting drift ratios and reducing damage. During the design stage, seismic isolation-system parameters must be carefully calibrated to control different aspects of the response, and it is necessary to run multiple simulations and count for parameter uncertainties. This research introduced components for seismic isolation and incremental dynamic analysis procedures integrated with framework modules, such as uncertainty quantifications and damage and loss estimation. Furthermore, an illustrative case study was included to reflect the impacts of this development.

Artificial Neural Network model to predict the dynamic properties of sand-polyurethane composite materials for GSI applications

This study shows the modelling of the dynamic properties of sand-polyurethane composite materials through the Artificial Neural Network method (ANN). Such properties are relevant to assess the effectiveness of polyurethane injected into the foundation soil as Geotechnical Seismic Isolation (GSI) system. Three FeedForward Neural Network (FFN) models are developed for the prediction of the shear modulus decay, the normalised shear modulus decay and the damping ratio curve. Four inputs are considered, namely the dynamic properties of pure sand and pure polyurethane, the volumetric percentage of polyurethane and the isotropic confining stress. Each model is trained and tested on a database including previous experimental results of Resonant Column (RC) tests performed on layered sand-polyurethane specimens, with polyurethane volumetric percentages varying from 10% to 30%. In all cases, the network architecture is found to be optimal with a single hidden layer and the number of hidden neurons from 4 to 6 according to the complexity of the data to be fitted. By comparing the predicted properties with the experimental results, a good prediction quality of the models is shown both in terms of the coefficient of correlation R2 and the Mean Squared Error MSE. A relative importance analysis finally reveals that polyurethane mainly affects the properties of the composite materials with its volumetric percentage, rather than its dynamic properties especially in terms of shear modulus.

Design of lead-rubber-bearing isolation systems using a grasshopper optimisation algorithm

Seismic isolation is an efficient method for improving the seismic behaviour of building structures. Sensitivity analysis of the behaviour of base-isolated structures is essential for investigating the effects of various mechanical and environmental factors on the performance of seismic isolation systems. In this study, the optimal design of a lead-rubber-bearing seismic isolation system was investigated by considering irregular mass conditions and near-fault seismic excitation. The grasshopper optimisation algorithm was used to optimise the design of the isolation system. Sensitivity analysis of the seismic response of the isolated structures was carried out for the mechanical parameters of the isolation system, mass irregularity in the building and near-fault earthquakes. The results proved the efficiency of the algorithm in optimal design problems for structural isolation systems. Also, the sensitivity analysis of the seismic behaviour of base-isolated structures showed that the yield base shear index had the most important effects in analysis. Furthermore, mass irregularity showed a negligible influence on the behaviour of the isolated structures.

Partially restrained seismic isolation system to retrofit a continuous girder RC bridge

The present paper proposes a partially restrained seismic isolation (PRSI) system to retrofit existing continuous girder reinforced concrete (RC) bridges. It involves a pure-friction system with a self-centring force provided by the stiffness of the deck and the frictional forces generated at the area of contact acting as an energy dissipation mechanism. The advantage is that the very small height of the system allows its application to existing bridges. The dynamic response until the collapse of an existing bridge subjected to seismic accelerations was assessed through a detailed 3D numerical model. This numerical model employed an explicit integration scheme that avoids numerical convergence drawbacks as a result of the strength and stiffness degradation of concrete structures. It was able to identify collapse mechanisms such as the development of cracks in the concrete elements. The seismic response of the original bridge was compared with that resulting from structural rehabilitation through implementation of a P-F type isolator in combination with the PRSI technique, which provided the system with a restitutive mechanism minimizing residual deformations. In addition, a classic structural reinforcement was incorporated by means of steel jacketing of the column. Both structural rehabilitation strategies were compared under the same seismic actions, assessing their efficiency and highlighting their benefits.

Temporal variations of the ambient seismic field at the Sardinia candidate site of the Einstein Telescope

SUMMARY Einstein Telescope (ET) is a proposed underground infrastructure in Europe to host future generations of gravitational-wave (GW) detectors. One of its design goals is to extend the observation band of terrestrial GW detectors from currently about 20 Hz down to 3 Hz. The coupling of a detector to its environment becomes stronger at lower frequencies, which makes it important to carefully analyse environmental disturbances at ET candidate sites. Seismic disturbances pose the greatest challenge since there are several important mechanisms for seismic vibrations to produce noise in ET, for example, through gravitational coupling, stray light, or through harmful constraints on the design of ET’s control system. In this paper, we present an analysis of the time-variant properties of the seismic field at the Sardinia candidate site of ET connected to anthropogenic as well as natural phenomena. We find that temporal variations of source distributions and of the noise spectra generally follow predictable trends in the form of diurnal, weekly, or seasonal cycles. Specific seismic sources were identified such as road bridges, which produce observable disturbances underground. This information can be used to adapt a detector’s seismic isolation and control system.

Shaking table experiments on framed structure resting on geogrid reinforced geotechnical seismic isolation system

Shaking table experiments on framed structure resting on geogrid reinforced geotechnical seismic isolation system

Rubber-soil mixtures: use of grading entropy theory to evaluate stiffness and liquefaction susceptibility

Rubber-soil mixtures are known to have mechanical properties that enable their use in backfills, road construction or geotechnical seismic isolation systems. The complexity of these mixtures comes from adding soft (i.e. rubber) particles that increases the number of particle properties to consider when studying the macroscopic behaviour. The distinction between sand-like and rubber-like behaviour is normally presented in relation to the rubber content and size ratio between particles. It is however unknown how the change on the mixture gradation affects the mechanical behaviour of RSm. Entropy coordinates condense the entire particle size distribution (PSD) to a single point on a Cartesian plane, accounting for all the information in the gradation. Grading entropy coordinates have been used to study typical geotechnical behaviours of mostly incompressible (i.e. sand) soils. In this study, entropy coordinates are used to analyse the correlation between the small-strain stiffness and liquefaction susceptibility of RSm and their PSDs. The results suggest that entropy coordinates can be used effectively on RSm as an alternative means of assessment of typical soil behaviours, being also able to distinguish between sand-like and rubber-like behaviours. Based on the 30 PSDs analysed, it is also evidenced that internal stability criterion proposed by Lőrincz (1986) can be used to predict the liquefaction susceptibility of RSm. The normalised base entropy (A) has also been shown to increase with the rubber content, which is linked to a lower liquefaction susceptibility, due to the supporting effect of rubber particles on strong-force chains formed of sand particles.

Mechanical properties of innovative prefabricated friction pendulum bearing with concrete-filled steel tube system

An innovative prefabricated seismic isolation system known as a friction pendulum bearing with a concrete-filled steel tube (FPB-CFST) was proposed to improve the mechanical performance and accelerate the construction process of the isolation layer. Unlike the traditional friction pendulum bearing-pier system, which consists of a cast FPB isolator and two cast-in-place reinforced concrete buttresses, the CFST was selected as the main supporting structure, and a spherical curvature surface (SCS) manufactured by a pressing process was attached to the CFST to slide the superstructure in the proposed FPB-CFST system. A construction procedure for the FPB-CFST was proposed, and a series of FPB-CFST specimens with various SCS radii were fabricated. The axial local compressive and compressive shear behaviors of the FPB-CFST were experimentally investigated. Friction coefficient tests were conducted to gain insight into the friction of the FPB-CFST. The mechanism of the proposed FPB-CFST subjected to axial local compression and compressive shear was discussed. The effects of sliding velocity and equivalent pressure of the bearing material on the friction coefficient were evaluated. The influences of the radius of the SCS and local compression ratio on the behavior of the FPB-CFST were addressed. The force model and design method of an FPB-CFST subjected to axial local compression and compressive shear are presented.

A geotechnical seismic isolation system based on marine sand cushion for attenuating ground shock effect: Experimental investigation

In this paper, an experimental study is introduced on the feasibility of applying a geotechnical seismic isolation system based on marine sand cushion (GSI-MSC) to resist explosion-induced ground shocks. The isolation system is characterised by low cost, easy availability, and slippage limitations, and it is particularly suitable in the protection of engineering structures during emergencies. Laboratory experiments on a steel tank structure were performed using a self-developed explosion shock and vibration simulation platform. The attenuation effects of the isolation system on ground motion, superstructural vibration and structural deformation were analysed. The results showed that GSI-MSC can reduce the intensity of ground shock, decrease the amplification effect of structural vibration, and weaken structural deformation. The attenuation effects were significantly enhanced with an increase in sand cushion thickness. The isolation mechanism was revealed from the perspective of spectrum analysis. The decreased lateral stiffness and reduced damping ratio improved the soft layer effect and internal energy dissipation of the sand cushion. This in turn led the GSI-MSC to exhibit a better harmonic attenuation effect over a wider range of high frequencies, beginning at a lower threshold. After isolation, the principal frequency of the ground motion decreased while the amplitude of high-frequency harmonics decreased, resulting in the weakening of the superstructural dynamic response. This indicated that the isolation system has a more stable attenuation effect on the low-period structures.

Nonlinear signal‐based control for shake table experiments with sliding masses

AbstractThis study introduces the first application of nonlinear signal‐based control (NSBC) to shake table experiments with sliding masses. NSBC utilising a nonlinear signal was specifically developed for nonlinear system control. In shake table experiments with a steel structure, it realised a seismic acceleration record on the table with near 100% accuracy even when the structure displayed nonlinear characteristics due to yielding of its components. Regarding the severity, sliding is stronger than yielding because of the rapid shifts of stick and slip states. Sliding is utilised for structural damage mitigation in seismic isolation systems, which are prominent devices in earthquake engineering. However, when sliding occurs on a shake table, it significantly jeopardises the table control. Thus, this study investigates the performance of NSBC to shake table experiments involving the phenomenon. First, this study examines the effectiveness of NSBC via numerical simulations on a shake table with a sliding interface, demonstrated by the Karnopp model, with a friction coefficient of 0.2. Subsequently, a linear model is designed based on the stability analysis of NSBC to assess stability margins obtained from different models. Experiments are performed by placing masses weighing approximately twice the table weight on sliding interfaces with friction coefficients of 0.2–0.4. In these experiments, NSBC with a reasonable linear model design realised expected acceleration records with sufficiently high accuracies, whereas inversion‐based control failed. This study verifies the effectiveness of NSBC for shake table experiments with sliding masses.

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.

Base isolation retrofitting design for the existing 2-story stone building and its Conversion into a 3-Story kindergarten

Recently the Armenian Missionary Association of America (AMAA) has approached the author of this paper with the request to carry out base isolation retrofitting design for the existing 2-story building with stone bearing walls and to simultaneously convert it into a 3-story kindergarten. In Armenia seismic isolation of existing buildings is becoming a more common method of providing protection from earthquake damage. Thanks to the author’s works in nowadays Armenia is well known as a country where seismic (base and roof) isolation systems are widely implemented in construction of new and retrofitting of existing buildings. The number of seismically isolated buildings per capita in Armenia is one of the highest in the world – second after Japan. The paper given below emphasizes that Armenia achieved significant results also in local manufacturing/testing of seismic isolation laminated rubber-steel bearings (SILRSBs). Several remarkable projects on retrofitting by base isolation of the existing buildings like apartment, school, hotel and hospital buildings are briefly mentioned in the paper to demonstrate the retrofitting experience accumulated in Armenia. Based on the gained experience further developments take place and unique base isolation structural concepts and technologies created by the author are applied more and more to the existing buildings. In this paper base isolation retrofitting design and analysis by the Armenian Seismic Code for the 2-story building with stone bearing walls is described. This will be a first application of base isolation retrofitting technology to an existing stone building with simultaneous increase of the number of its floors by one. The other important factor is that applied structural concept allows retrofitting by base isolation when reconstruction works in superstructure and construction of the additional 3-rd floor were going on in the same time.

Comparative Study of the Non-Linear Dynamic Behaviour of Different Seismic Isolation Systems

To mitigate the effect of earthquake on the structure, the base isolation technique is the best alternative as a seismic protection system. In this research, a two-degree-of-freedom (2DOF) equivalent model is modelled based on a real eight-level reinforced concrete structure damaged by the Boumerdes earthquake in 2003 is presented. The basic isolation systems considered are four models namely: the first system is a high damping isolator (HDBR), the second system is the friction pendulum isolator (FPS). The third model of the base isolation system is a non-linear model with two horizontal and rotational stiffness springs (SHRS), and finally the last model presents a bilinear spring (SB). The isolators are designed according to the UBC-97 code. Earthquake recordings from Dar-El-Beida of the 2003 Boumerdes earthquake were used as seismic load. A dynamic analysis of the comparative temporal responses of the structure was performed by comparing its dynamic behaviour with that of the fixed base structure. The results obtained reveal a reduction in base shear, stage drift and stage acceleration and an increase in displacement and time period for the structure isolated at the base. The results are presented in tables and graphs.

Seismic isolation effect of rubber-sand mixture cushion under different site classes based on a simplified analysis model

The use of rubber-sand mixture (RSM) cushion in geotechnical seismic isolation (GSI) systems is an emerging technique for protecting buildings in earthquake-prone areas. The advantage is that RSM with high shear resistance and low shear modulus improves the foundation soil, allowing seismic energy to be partially dissipated in the cushion before it is transmitted to the structure. However, the isolation effect of the RSM cushion considering site classification has not been recognized due to the complexity of the problem. In this paper, a simplified analysis model is established to study the seismic performance of the RSM cushion, in which 195 ground motion records are obtained from different site conditions according to the Code for Seismic Design of Buildings GB50011-2010, reflecting the influence of site classification. By using the developed theoretical analysis method, the seismic isolation effect of the RSM cushion under different site classes is investigated. The key influencing factors to be considered include the cushion thickness, base pressure and seismic excitation intensity. The results show that: 1) The isolation effect of the underlying RSM cushion on the superstructure is affected by site classification. The harder the site, or more specifically, the shorter the predominant period of the site, the better the isolation effect of the RSM cushion. 2) For the same site classification, the isolation effect increases with increasing cushion thickness, base pressure and seismic excitation intensity. In particular, the robustness of the seismic performance of the RSM cushion deteriorates upon reaching a cushion thickness of 500 mm, and this deterioration in robustness is independent of site classification. Overall, the present study is the first systematic analysis of the effects of ground motion on GSI systems with RSM as the core under different site classes, and the research findings are of great significance for the low-cost seismic design of residential houses in developing countries.

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.