Seismic Isolation Research Articles

Impact of surface-reflected seismic waves on the seismic isolation performance of circular tunnel isolation layers

Impact of surface-reflected seismic waves on the seismic isolation performance of circular tunnel isolation layers

Multi-Performance Economical Optimization of Base Isolation System with Tuned Inerter Negative Stiffness Damper Subjected to Non-Stationary Seismic Excitation

Base isolation proves to be an effective vibration control strategy for buildings. However, the base-isolation floor (BIF) may undergo substantial displacements. To improve the seismic performance of base-isolation system, this paper proposes a multi-performance economical optimization procedure (MPEOP) for exploring the optimal parameters of base isolation system with tuned inerter negative stiffness damper (BIS-TINSD) subjected to non-stationary seismic excitation. The simplified analysis model for BIS-TINSD is developed, followed by the formulation of the state-space representation. The non-stationary seismic excitation is represented as a stationary Gaussian process with a time-modulating function based on the Clough–Penzien spectrum, and combining the equations of motion with seismic excitation results in the augmented state-space representation of structure-damper-excitation, followed by the formulation of differential Lyapunov equation. The multi-objective performance economical index is proposed, in which the performance optimization objective is defined as a weighted combination of base isolation floor displacement and superstructure acceleration, and the economic optimization objective is set as the support stiffness. The Pareto optimal fronts (POF) are adopted to deal with optimal objectives. The examination of optimal design parameters is extended under real earthquake records. The results demonstrate the effectiveness of the MPEOP, and indicate the advantages of the BIS-TINSD compared with the inerter amplify damper (IAD) and negative stiffness inerter damper (NSID).

Evaluation and Performance Testing of Eccentric Rolling Isolation System

Seismic isolation has become a widely accepted method for the protection of structures and nonstructural components. However, this control strategy is unfavorable against near-fault earthquakes, particularly those featuring velocity-pulse effects. Excessive isolation displacements and accelerations can occur during such earthquakes, resulting in amplified responses of the superstructure. To resolve this problem, this study develops a prototype of the eccentric rolling isolation system consisting of one platform eccentrically pin-connected to four circular rollers. The eccentric pin connection yields a nonlinear restoring force of the proposed system and results in displacement-dependent resonances, and the inherent mechanical friction also yields an energy dissipation capability of the system. As the magnitude of ground excitation increases, the prototype system generates a lower resonant frequency away from the dominant frequencies of earthquakes. This behavior is experimentally investigated and verified for mechanical behavior and seismic performance. In the experiment, sinusoidal, far-field, and near-fault ground motions are considered in shaking table testing. Some parameters, such as the eccentricity, roller size, and inertial force, are also experimentally investigated. As found in the experimental result, the feasibility of the prototype system is successfully verified. Meanwhile, the comparable simulation results further validate the mathematical model of the prototype system. Consequently, the eccentric rolling isolation system has demonstrated isolation effectiveness against far-field ground motions and has good potential to perform better than a linear system under near-fault ground motions.

Seismic Isolation Materials for Bored Rock Tunnels: A Parametric Analysis

Most recent tunnel designs rely on more thorough analyses of the intricate rock interactions. The three principal techniques for excavating rock tunneling are drill-and-blast for complete or partial cross-sections, TBM only for circular cross-sections with full faces, and road header for small portions. Tunnel-boring machines (TBM) are being utilized to excavate an increasing number of tunnels. Newer studies have demonstrated that subterranean structures such as tunnels produce a variety of consequences during and after ground shaking, challenging the long-held belief that they are among the most earthquake-resistant structures. Consequently, engineering assessment has become crucial for these unique structures from both the geotechnical and structural engineering standpoints. The designer should evaluate the underground structure’s safety to ensure it can sustain various applied loads, considering both seismic loads and temporary and permanent static loads. This paper investigates how adding elastic, soft material between a circular tunnel and the surrounding rock affects seismic response. To conduct the study, Midas/GTS-NX was used to model the TBM tunnel and the nearby rock using the finite element (F.E.) method to simulate the soil–tunnel interactions. A time–history analysis of the El Centro (1940) earthquake was used to calculated the stresses accumulated in the tunnels during seismic episodes. Peak ground accelerations of 0.10–0.30 g, relative to the tunnel axis, were used for excitation. The analysis utilized a time step of 0.02 s, and the duration of the seismic event was set at 10 s. Numerical models were developed to represent tunnels passing through rock, with the traditional grout pea gravel vs. isolation layer. A parametric study determined how isolation material characteristics like shear modulus, Poisson’s ratio, and unit weight affect tunnel-induced stresses. In the meantime, this paper details the effects of various seismic isolation materials, such as geofoam, foam concrete, and silicon-based isolation material, to improve protection against seismic shaking. The analysis’s findings are discussed, and how seismic isolation affects these important structures’ performance and safety requirements is explained.

Predicting crosswind response of tall buildings: Base isolation and nonlinear aeroelastic effects

This study introduces an analysis framework to evaluate the crosswind response of tall buildings under the influence of base isolation and nonlinear aeroelastic effect near the vortex lock-in wind speed. The motion-induced and buffeting forces are determined based on those in a building with a fixed base. The primary focus is on modeling the motion-induced force in tall buildings with base isolation, where no pre-existing model exists. The fundamental modal displacement is used to describe the building motion relative to the base. The Bouc-Wen model is employed to capture the hysteresis in the relation of shear force and displacement of the isolation system. Through response history analysis, the response statistics of a 65-story building with a square cross-section are determined and compared with those of a fixed-base building. An investigation is conducted to examine the impact of different isolation layer parameters on building response. Additionally, this study explores how the motion-induced force model influences the building response. The findings indicate that base isolation effectively mitigates nonlinear aeroelastic effects, leading to a significant reduction in crosswind response.

Analisis Perbandingan Fluid Viscous Damper dan Fixed Base Terhadap Beban Siklik dengan Finite Element

The geographical location of Indonesia, which is very at risk of earthquake disasters, requires the planning of building structures that are resistant to earthquake risks, one of which is by using base isolators. A base isolator system can improve structural performance by dissipating earthquake energy with its flexibility character to increase the vibration period. One type of base isolator is the Fluid Viscous Damper (FVD), which can be applied to high-rise buildings that often experience destruction during earthquakes. This research aims to determine the energy dissipation and ductility of fixed base structures and structures using FVD with finite element method using ABAQUS application. The object of analysis of this study uses a two-story portal with a steel structure. The results of this study obtained the characteristics of the two building models are semi-ductile, but there are differences in the ductility value between the two models. Based on the calculation results, the deviation ductility value that occurs in the fixed base building model is 2.624. Meanwhile, the deviation ductility of the FVD building model is 4.104. The use of FVD can increase the ductility value by 22%. The dissipation that can be done by the fixed base building model is 0.119, and the energy dissipation value for the building model with FVD is 0.156. Using FVD can increase energy dissipation in the analyzed model by 13.45%.

Vulnerability of reinforced concrete frames using anti-seismic hysteretic devices for the Lorca earthquake (2011)

Many buildings around the world are extremely vulnerable to serious and moderate earthquakes. Base isolation and energy dissipators are the traditional techniques in anti-seismic designs. The present paper focuses on the suitability of using hysteretic energy dissipators in braced buildings in low-to-medium seismic zones, such as southeast Spain. To this end, static (Push-over) and dynamic analyses have been carried out using the record of the Lorca earthquake (2011) in its most unfavorable direction (N-S), using reinforced concrete frames of low (5 stories frame), medium (10 stories frame), and high height (15 stories frame) with hysteretic dissipators (based on metal plasticization) and economical and easy-to-use devices. The results show that this type of solution is appropriate in the case described and indicate the advantages and disadvantages of its use in buildings in the study area. The results show that the effectiveness of the dissipative devices increases with the height of the frames, in terms of displacements, resistance, and distribution of moments in the primary structural elements of the frames (beams and columns).

The nonlinear negative stiffness inertial amplifier base isolators for dynamic systems

The nonlinear negative stiffness inertial amplifier base isolators (NNSIABI) for vibration reduction of dynamic systems are introduced in this paper. H 2 and H ∞ optimization methods are applied to derive the exact closed-form expressions for the optimal design parameters of novel isolators. For SDOF system, the dynamic response reduction capacity of H 2 and H ∞ optimized linear NSIABI are significantly 64.78% and 77.14% superior to the optimum traditional base isolators. In contrast, the dynamic response reduction capacities of H 2 and H ∞-optimized nonlinear NNSIABI are significantly 64.66% and 66.56% superior to the optimum traditional base isolators. For MDOF systems, the optimum linear NSIABI’s dynamic response reduction capacities are significantly 95.06% and 97.80%, superior to the optimum traditional base isolators. In addition, the optimum nonlinear NNSIABI are significantly 94.88% and 97.68%, superior to the traditional base isolators. All the results are mathematically corrected and applicable for practical applications.

Investigations on seismic performance of nuclear power plants equipped with an optimal BIS-TMDI considering FSI effects

This paper introduces a base isolation system-tuned mass damper inerter (BIS-TMDI) hybrid system to the AP1000 nuclear power plant (NPP), which reduces seismic damage potential of the NPP structure. The effects of fluid-structure interaction (FSI) caused by the passive containment cooling system water storage tank (PCCWST) on NPP's seismic performance are investigated. The FSI of water tank theoretical model is considered based on the Housner's model, and a series of time history analyses are performed to prove the rationality of the proposed model. Three single-objective optimization strategies are employed to minimize the relative displacement variance and absolute acceleration variance of the upper structure, as well as the filtered energy index (FEI). Furthermore, a multi-objective optimization strategy considering all these three indexes is proposed to obtain optimal parameters of vibration control. The influence of vibration control strategies on the relative deformation and acceleration of the upper structure is explored with various water level ratios. The analytical results indicate that the proposed BIS-TMDI strategy has significantly reduced the NPP structure's seismic response. The effectiveness of the vibration control strategy is influenced by the water level ratio, emphasizing the significance of designing an appropriate water level ratio to reduce NPP structure's seismic response.

Exploit the study of the scenarios for the control of the response of single-degree-of-freedom systems with bumpers

In earthquake-prone areas, seismic isolation systems are designed to preserve structural safety and prevent occupants’ injury and properties’ damage. However, seismically isolated structures can be subject to large displacements relative to the ground under earthquakes, which lead to define two problems, the first problem concerns to excessive displacements, whereas the second problem relates to excessive accelerations that occur when the displacements are limited by an obstacle with high relative stiffness. An arrangement that favors the solution of these problems is an appropriate interposition between the isolated structure and the obstacle of the shock absorbers or bumpers. The aim of this paper is to investigate, via numerical parametric analyses, the possibility to exploit the occurrence of impact in a two-sided vibro-impact isolated single-degree-of-freedom (SDOF) system under harmonic base excitation with beneficial effects. Through the analysis of the response scenarios which can occur varying the obstacles’ parameters, that is the width of the gap and the mechanical (stiffness and damping) properties, the target is to reduce both the maximum value of the displacement and of the acceleration of the mass, compared to the free flight condition, without possibly reducing the vibration isolation frequency range. This research path leads to the definition of vibro-impacting control systems and to the free and constrained single and multi-objective optimal design of the control system consisting of the integrated assembly of the isolation system, bumpers and gaps. The main results obtained consist in having (i) found a unique optimality condition, (ii) calculated the dissipated energy and given an energetic interpretation to the optimality condition (iii) built maps, that allow to advance behavior predictions, provide indications on the design and allow to make evaluations of the performance of the vibro-impacting system as a function of the stiffness and damping parameters and of the width of the gap. The stiffness ratio and the damping ratio, which define the mechanical properties of the bumpers, are such that the dimensionless relaxation time is about 1, (iv) finally the results are compared to multi-objective optimal design. Ultimately, the advantages of this new isolation system are: (1) provide a physical limit switch to the isolation system in order to limit the maximum displacement of the mass; (2) reduce the effects of amplification dynamics in the resonance zone; (3) reduce the static displacement, all without possibly modifying the dynamic response in the isolation zone.

Assessing the significance of nonlinear rotational behavior in high damping rubber bearings for seismic performance of base‐isolated RC frame building

AbstractUtilizing high‐damping rubber bearings (HDRBs) for seismic isolation significantly enhances building seismic performance. However, previous studies have often neglected the nonlinear rotational behavior of these bearings when assessing base‐isolated systems using HDRBs. This study introduces two numerical models of the HDRBs, each comprising six springs. The first model, referred to as the BIL model, assumes linear behavior for the rotational degrees of freedom of the bearings. The second model, referred to as the BINL model, accounts for the nonlinear rotational behavior. The parameters of the bearing shear springs and the rotational springs of the two models are calibrated using experimental data. In order to investigate the influence of nonlinear rotational behavior of HDRBs on the seismic performance of base‐isolated buildings, nonlinear time history analysis is conducted on a six‐story base‐isolated RC frame building. Comparative analysis between the BIL model and the BINL model covers bearing behavior, superstructure response, and energy dissipation distribution. Results indicate a significant influence of considering nonlinear rotational behavior on column bending moments. These findings provide crucial insights for enhancing seismic design strategies for base‐isolated buildings.

Performance parameter design of seismic isolation bearings for high-speed railway simply-supported bridges using neural network

In the simply-supported bridge system for the high-speed railway with unequal pier heights, the intrinsic relationship between the seismic isolation bearing parameters and the seismic performance objectives of the bridge is very complex. It is not easy to establish a precise mathematical model, and the design process of the bearings relies heavily on the experience of the designers. This paper uses an artificial neural network (ANN) to design the seismic performance of seismic isolation bearing. Considering that the triple friction pendulum bearing (TFPB) can adaptively change the stiffness under different seismic levels, the ANN model fits the mapping relationship between the parameters of the TFPB and the seismic performance objectives. Four evaluation indexes are used to verify that the ANN model has good generalization ability. A case study shows that the designed bearing meets the expected seismic performance requirements, which verifies the applicability of the ANN model.

Energy Dissipation Efficiency of Geotechnical Seismic Isolation with Gravel-Rubber Mixtures: Insights from FE Non-Linear Numerical Analysis

ABSTRACT This paper provides new and useful insights into the performance and efficiency of geotechnical seismic isolation (GSI) systems with gravel-rubber mixtures containing 10%, 25% and 40% volumetric rubber content (VRC). Finite element numerical models were developed in OpenSees and subjected to sinusoidal ground motions with varying input base acceleration and frequency. The best seismic performance was attained for VRC = 40% at a frequency of 8 Hz. Using a newly developed GSI efficiency index, the energy dissipation efficiency of VRC = 40% was found to vary between good to excellent, while that of VRC = 10% and 25% is poor.

Seismic isolation design and analysis of a complex medical building

Seismic isolation design and analysis of a complex medical building

Sustainable and Economic Base Isolators Made by Scrap Tires for Low-rise Buildings in Developing Countries

Sustainable and Economic Base Isolators Made by Scrap Tires for Low-rise Buildings in Developing Countries

Parameter Optimization of Friction Pendulum Bearings Based on the Adaptive Genetic Algorithm Considering the Overall Evolutionary Status

Improper design of friction pendulum bearings can lead to poor seismic reduction performance and may result in the failure of local vulnerable components. And the parameter design of friction pendulum bearings mainly relies on experience and verification calculations at present. This paper proposes an adaptive genetic algorithm considering the overall evolution state of the population, adjusting crossover and mutation probabilities adaptively based on individual fitness and population diversity. Compared to traditional algorithms, it exhibits better global search capabilities and convergence efficiency. Combining the improved genetic algorithm with finite element models, a parameter optimization method is proposed. The parameters of friction pendulum bearings are optimized. In response to the situation in this paper, the optimal friction coefficient of the friction pendulum bearing is determined to be 0.01 and the optimal equivalent radius is 3.3 m. This can provide a reference for the design of seismic isolation devices.

Comparative Analysis of G+15 Building with and Without Lead-Bearing Rubber Base Isolators Using Etabs

Comparative Analysis of G+15 Building with and Without Lead-Bearing Rubber Base Isolators Using Etabs

The Role of a Simple Inerter in Seismic Base Isolation

The present study investigates the role of a simple inerter in supplemental devices for possible implementation in the mature seismic base isolation technique. Firstly, the response of the base-isolated structure with an optimally tuned mass damper inerter (TMDI) is investigated to see the tuning effects. The time required to tune the TMDI was found to be significantly longer than the duration of a strong-motion earthquake. There was still a reduction in the response of the isolated structure, which is primarily due to the added damping and stiffness (ADAS) of TMDI and not because of the tuning effects. Hence, it is proposed that the corresponding ADAS of the TMDI be directly added to the isolation device. Secondly, the response of the base-isolated structures to the fluid inerter damper (FID) is studied. It was observed that the inerter of the FID does not influence the displacement variance of an isolated structure under broadband earthquake excitation. It implies that the response of the isolated structure to FID is primarily controlled by its counterpart fluid damper (FD). The performance of optimal TMDI, ADAS, FID, and FD to mitigate the seismic response of the flexible multi-story base-isolated structure under real earthquake excitations is also investigated. In terms of suppressing the displacement and acceleration responses of the isolated structure, it has been found that TMDI and ADAS perform similarly. Comparing the response of the isolated structure with FID and FD demonstrated that the inerter in the FID has detrimental effects on the isolated structures, in which the top floor’s acceleration and base shear are substantially increased.

Evaluation of stiffness and damping of a base-isolated building considering higher-order modes

Introduction: Structural health monitoring (SHM) is an effective method of understanding the seismic safety of seismic design models and the continued use of buildings after earthquakes. Various system identification methods applicable to SHM have been proposed; however, most target only superstructures. Their applicability for evaluating the soundness of foundations and soil structures should also be examined. In addition, evaluating high-order modes in addition to low-order modes is necessary to capture changes in the vibration characteristics of superstructures, foundations, and soil structures. However, the impact of considering higher-order modes on the identification results has not been sufficiently evaluated. This study aims to address these issues by clarifying the importance of considering higher-order modes and proposing a method that can contribute to improving the accuracy of future building health evaluation methods.Methods: This study proposes a method of evaluating the stiffness and damping of a superstructure and dynamic soil spring considering low-order to high-order modes using the efficient transfer function fitting system for a base-isolated (BI) building. First, numerical experiments were performed to examine the accuracy of the proposed method in evaluating the stiffness and damping of each part when using acceleration data from limited observation points. Furthermore, this method was applied to an existing BI building subjected to the 2011 off the Pacific Coast of Tohoku Earthquake (2011 Tohoku Earthquake) to identify each parameter while considering higher-order modes. In addition, secular changes and the amplitude dependence of each structure were analyzed.Results: The results showed that the stiffness and damping of the seismic isolation layer, superstructure, and dynamic soil spring were stable with little variation owing to aging; however, the influence of amplitude dependence was relatively large.Conclusion: The significance of considering higher-order modes in evaluations of the soundness of foundations and soil structures was demonstrated. Moreover, the response characteristics of earthquakes recorded from 2007, before the 2011 Tohoku Earthquake, up to 2023 were accurately reproduced through numerical simulation by considering the amplitude dependence of the identified physical parameters based on the proposed identification framework.

Comprehensive Assessment of the Seismic Performance of an Innovative Hybrid Semiactive and Passive State Control System for a Low-Degree-of-Freedom Structure Using Real-Time Hybrid Simulation

The dynamic performance of base isolation systems provides an effective means to reduce the seismic vulnerability of buildings. However, large displacements in the base isolation during seismic events pose a major challenge for this control system. Recently, novel control systems have been implemented to control and reduce the excessive displacements. This study presents an evaluation of the seismic performance of unconnected-fiber-reinforced elastomeric isolators (U-FREI) and variable orifice damper (VOD) devices used together as a hybrid control system for a low-degree-of-freedom reference structure by employing real-time hybrid simulation (RTHS) testing technique. This physical cybernetic testing methodology allows a dynamic system of interest to be substructured into two components: numerical and experimental. In this study, the numerical substructure corresponds to a 2-degree of freedom model, representing a reference structure, and an experimental substructure was formed using the hybrid control system described. To develop an interface between the two substructures, a horizontal transfer system (HTS) was implemented and coupled with a vertical transfer system (VTS). Using RTHS, the performance of the reference structure and the hybrid control system was evaluated under six seismic events: CAM, CAT, El Centro, Loma Prieta, Pizarro, and Chihuahua, at a maximum acceleration of 0.10 g (0.981 m·s−2). The experimental behavior of the hybrid control system allows the reference structure to reduce its maximum drift by more than 24% compared to the fixed structure. Finally, the performance and accuracy of the RTHS tests were calculated.