Hybrid Isolation System Research Articles

Research on a Bridge Hybrid Isolation Control System Based on PID Active Control and Genetic Algorithm Optimization

A bridge hybrid isolation system, integrating both active and passive control strategies, is proposed and investigated to enhance seismic performance. The system is modeled as a two-layer structure, with the upper layer subjected to active control via a Proportional–Integral–Derivative (PID) controller, and the lower layer employing a conventional passive base isolation system. The displacement response of the superstructure is minimized by the control forces generated by the PID controller, which also accounts for the reaction forces transmitted to the lower isolation layer. To optimize the controller’s performance, a genetic algorithm is implemented for real-time tuning of the PID parameters. Numerical simulations, conducted using the Newmark method, are employed to assess the influence of active control on the lower isolation system. The results reveal that, while active control increases the peak displacement of the superstructure to some extent, it significantly prolongs the structural period, thus enhancing the system’s overall seismic resilience and stability.

Nonlinear seismic assessment for nuclear power plants with structural-geotechnical hybrid isolation strategy

Improving the seismic resilience of nuclear power plants (NPP) to withstand super-strong earthquakes is critical for ensuring nuclear safety. Seismic isolation can effectively enhance the structural seismic margins and has significant potential for development in NPPs. Although three-dimensional (3D) base isolation can effectively isolate tri-directional ground motion, it also faces challenges such as the limitations of horizontal and vertical displacements of the isolation layer under super-strong earthquakes. In this paper, a novel hybrid passive control strategy that combines 3D base isolation with geotechnical seismic isolation (GSI) systems is proposed. Furthermore, a nonlinear soil-structure interaction analysis method is developed and the program is validated using numerical examples. Finally, a nonlinear dynamic analysis of a large-scale nuclear island building at a non-bedrock site is conducted to investigate the seismic mitigation effects of a hybrid isolation system under super-strong earthquakes. The research findings demonstrate a significant improvement in the isolation effectiveness of the proposed strategy compared to 3D base isolation, which further reduces the tri-directional seismic responses of NPPs while also exhibits the ability to control the deformation in the isolation layer. The proposed hybrid isolation system can significantly improve the ability of NPPs to withstand super-strong earthquakes and provide support for the hybrid seismic isolation design of NPPs.

Seismic Isolators Layout Optimization Using Genetic Algorithm Within the Pymoo Framework

In most previous studies, seismic base isolation system optimization has mainly focused on determining isolation layer parameters. However, the subsequent steps of isolator device selection and positioning can significantly impact overall system performance. To address these shortcomings, we propose an alternative optimization approach demonstrated through two models: regular and irregular 8-storey reinforced concrete structures. This approach utilizes the Pymoo framework and commercially available isolators to find optimal isolator layout configurations in two steps. First, using the equivalent lateral force (ELF) procedure, an initial population of seismic isolators meeting shear strain, base shear coefficient, and buckling requirements was randomly selected from suppliers' elastomeric bearing catalogs. Second, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to improve the seismic response of the models under the fast nonlinear analysis (FNA) method by minimizing peak roof acceleration, inter-story drift ratio, displacement of the isolated base layer, as well as maximizing the fundamental period. The results underscore the effectiveness of this approach in improving seismic response. Compared to fixed-base structures, the optimal solutions achieved more than double the fundamental period, reduced peak roof acceleration by over 70%, and diminished base shear force by approximately 50%. This methodology can serve as a reference for future research across various structure types, including hybrid isolation systems and steel structures. Doi: 10.28991/CEJ-2024-010-08-07 Full Text: PDF

Design and Experimental Study of a Hybrid Micro-Vibration Isolation System Based on a Strain Sensor for High-Precision Space Payloads.

Micro-vibrations significantly influence the imaging quality and pointing accuracy of high-precision space-borne payloads. To mitigate this issue, vibration isolation technology must be employed to reduce the transmission of micro-vibrations to payloads. In this paper, a novel active-passive hybrid isolation (APHI) system based on a strain sensor is proposed for high-precision space payloads, and corresponding theoretical and experimental studies are implemented. First, a theoretical analysis model of the APHI system is established using a two-degrees-of-freedom system, and an integral control method based on strain sensing is presented. Then, an electromagnetic damper, active piezoelectric actuator, and strain sensor are designed and manufactured. Finally, an APHI experimental system is implemented to validate the effectiveness of electromagnetic damping and strain-sensing active control. Additionally, the control effects of acceleration, displacement, and strain sensors are compared. The results demonstrate that strain sensors can achieve effective active damping control, and the control method based on strain sensors can effectively suppress the payload response while maintaining stability. Both displacement and strain sensors exhibit superior suppression effects compared with the acceleration sensor, with the strain sensor showing greater potential for practical engineering applications than the displacement sensor.

Stochastic Optimization of Electromagnetic Inertial Mass Dampers in Nonlinear Hybrid Base Isolation Systems Under Seismic Excitations

Recently developed inerter-based dampers have been installed at the base layer to reduce base displacement and simultaneously improve the superstructure’s performance. However, in the existing research on optimizing damper parameters, the nonlinear property of base isolation is simplified and stochastic linearization technique is introduced to approximate such nonlinearity, which would inevitably introduce errors. In this paper, an improved method is proposed for stochastic optimization of electromagnetic inertial mass dampers (EIMD) in nonlinear hybrid isolation systems subject to seismic excitations. First, a stochastic seismic excitation is represented by one elementary random variable adopting the dimension-reduction spectral representation method. Then, statistical moments of nonlinear base-isolated structural responses are estimated using two-point estimation method (2PEM). Finally, the EIMD optimal parameters are obtained via the modified directional bat algorithm (MDBA) recently proposed by the authors through minimizing base layer response moments. This proposed improved method could fully consider the base isolation nonlinearity compared with the previous stochastic linearization technique. Moreover, the proposed stochastic optimization of the EIMD only requires two dynamic analyses to achieve its efficiency. A seven-story base-isolated frame building equipped with an EIMD is investigated in the numerical simulation, and results indicate that EIMD optimized by this proposed method obviously outperforms the results by the stochastic linearization technique and the conventional viscous damper (VD) in the base layer displacement reduction.

Seismic resilient design and negative stiffness-assisted nonlinear isolation system for adjacent non-coaxial buildings linked by corridors

Adjacent non-coaxial buildings have been widely built owing to complementary functions, while the non-coaxial layout could cause a great torsion effect and seismic-induced damage. This study proposes a negative stiffness-assisted hybrid isolation system and a corresponding earthquake-resilient design methodology to upgrade the multi-performances of the adjacent non-coaxial buildings and linking corridors. The hybrid isolation system includes synthetic employment of various isolators and negative-stiffness amplification systems comprised of nonlinear viscous dampers for adjacent structures, as well as tailored friction bearing for linking corridors. The mechanical property and model of the adjacent non-coaxial buildings are established, based on which a typical case is introduced. Next, the conception of the earthquake-resilient design method and procedure is elaborated, following which the functionality of each component in the hybrid system is investigated. The advantages of the developed hybrid isolation system and design methodology are illustrated by a systematic parametric analysis and time history analysis for the typical case. The results show that the torsional effect can be a dominant problem in non-coaxial adjacent buildings, which can be solved by the flexibly tailored negative stiffness effect produced by the negative stiffness-assisted isolation system. The collaboration within the proposed hybrid isolation system can produce improved isolating and enhanced nonlinear energy dissipation effects on adjacent buildings, simultaneously limiting the isolation displacement without weakening the isolating effect. The optimized friction sliding bearings effectively reduce the relative torsion concentrated on the linking corridors with a maintained function. The hybrid isolation system and earthquake-resilient design can be adopted as a high-efficiency solution to the non-coaxial linked historic buildings with insufficient seismic resistance.

Full-scale shaking table tests and numerical studies of structural frames with a hybrid isolation system

A typical hybrid isolation system (HIS) incorporating natural-rubber bearings (NRBs) and nonlinear fluid viscous dampers (NFVDs) is proposed for seismic protection of critical equipment in nuclear power industrial buildings (NPIBs) under strong earthquakes. Design procedure with a parametric study towards the HIS considering various stiffness and damping values is first investigated via extensive nonlinear time history analyses. Then a preliminary recommendation for the specific structural demands of the considered system is proposed to direct the seismic design for both member- and system-level tests. Through a suite of full-scale shaking table tests on two typical NPIBs, the efficiency and reliability of the HIS are verified, in comparison to the structure with conventional rubber isolation system (RIS). The shaking table test results exhibit a superior behavior of the HIS in structural dual control strategies, i.e., transient acceleration control in critical equipment and bearing deformation control. Also, the HIS presents stable and resilient performances in both negligible residual bearing deformation and undetectable damage to structural/nonstructural components (containing the seismic isolated devices, i.e., NRBs and NFVDs). Finally, a three-dimensional finite element (FE) structural model and a single-degree-of-freedom (SDOF) system are successively developed to simulate the dynamic responses of the test structures. The well-validated SDOF FE model, serving as a reliable alternative for the isolated NPIBs, can be further utilized to facilitate practical design.

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 response mitigation of prefabricated industrial equipment structural frames through a hybrid isolation system

For reducing the excessive acceleration response of the critical equipment in a type of industrial equipment structural frames under strong earthquakes, a hybrid isolation system (HIS), incorporating linear natural rubber (LNR) and lead rubber (LR) bearings, is proposed. The efficiency and reliability of the HIS are verified through a series of full-scale shaking table tests on two prefabricated industrial moment resisting frames (MRFs), with respect to a corresponding fixed-base system (FBS). The structural dynamic characteristic and seismic performance of the two types of MRFs, i.e., reinforced concrete structure (RCS) and composite concrete-filled steel tube structure (CCFSTS), are examined both with the HIS and FBS subjected to a range of seismic intensities. The test results demonstrate the superior performance of the HIS in controlling transient acceleration response under near-fault, far-field and artificial ground motions. The average peak acceleration reduction coefficients (PARCs) of the HIS range between 75.60% and 79.51% in the two considered MRFs along two horizontal directions, with a strict satisfaction on the peak acceleration response for normal operation of the critical equipment. Also, the hysteretic behavior of the HIS is stable and controllable during the earthquake excitations. The peak transient displacement of the HIS is satisfactory, and the residual deformation is negligible even under the maximum considered earthquake (MCE) excitations. Besides, components of the two MRFs are undamaged during the whole test. Thus, with the capacity of protecting the acceleration-sensitive equipment and structural components, the proposed HIS possesses a great prospect in enhancing the structural resilience.

Preliminary results from push-and-release tests of a base-isolated building in Camerino, Italy

Experimental testing of a two-storey steel braced-frame building structure on a reinforced concrete slab isolated from the foundations resting on a steep slope through a hybrid system (high-damping rubber bearings and low-friction sliding bearings) is presented. The base-isolated building incorporates a permanent push-and-release device capable of displacement amplitudes as those induced by extreme seismic events and allowing the push-and-release tests to be repeated in the future. The tested building as well as its testing set up, whose cost represents a small increment of its construction cost if planned in the early stages of the design process, are presented. Afterwards, preliminary results from quasi-static push tests (slow loading and unloading) and push-and-release dynamic tests (slow loading and subsequent sudden release) are briefly described. Compared to push-and-release tests documented in the past, the activities presented in this article have peculiarities related to the building (typology, size, and foundation geometry), the magnitude of the maximum horizontal displacement achieved (284.6 mm), the possibility to repeat the same tests in the future, producing comprehensive sets of data for the analysis of the behaviour of the hybrid isolation system and superstructure.

Multi-Objective Optimization of Base-Isolated Tanks with Supplemental Linear Viscous Dampers

Base isolation of liquid storage tanks has proven to be an efficient seismic protection measure, leading to a drastic reduction of a superstructure’s distress. However, many such tanks are located near seismic tectonic faults, which generate strong pulse-like ground motions that can impose excessive displacement demands on the isolators. For this reason, viscous dampers are incorporated into the isolation system to avoid overconservative isolators design. To optimize the seismic performance of hybrid isolation systems consisting of single friction pendulum bearings and linear viscous dampers, two novel multi-objective optimization approaches are proposed in the current study. Furthermore, suitable constraint functions and design variables are selected, considering the most critical parameters of the hybrid isolation system. The multi-objective genetic algorithm optimizer is used for the solution of both problems. The results are presented in the typical form of Pareto and certain optimal design solutions are carefully chosen and compared in terms of isolators fragility curves and tank accelerations. The main aim is to optimize the critical design parameters by achieving a reasonable balance among contradicting objectives. The tank industry can substantially benefit from this study, as a more cost-efficient design of hybrid base-isolation can be attained for large-scale tanks.

Sliding Isolation Systems: Historical Review, Modeling Techniques, and the Contemporary Trends

Base isolation techniques have emerged as the most effective seismic damage mitigation strategies. Several types of aseismic devices for base isolation have been invented, studied, and used. Out of several isolation systems, sliding isolation systems are popular due to their operational simplicity and ease of manufacturing. This article discusses the historical development of passive sliding isolation systems, such as pure friction systems, friction pendulum systems, and isolators with other sliding surface geometries. Moreover, multiple surface isolation systems and their behavior as well as the effectiveness of using complementary devices with standalone passive isolation devices are examined. Furthermore, the article explored the various modeling techniques adopted for base-isolated single and multi-degree freedom building structures. Special attention has been given to the techniques available for modeling the complex phenomena of sliding and non-sliding phases of sliding bearings. The discussion is further extended to the development in the contemporary areas of seismic isolation, such as active and hybrid isolation systems. Although a significant amount of research is carried out in the area of active and hybrid isolation systems, the passive sliding isolation system still has not lost its appeal due to its ease of adaptability to the structures.

Push-and-release tests of a steel building with hybrid base isolation

Experimental testing of a two-storey 5875 square meters steel braced-frame structure resting on a reinforced concrete slab isolated from the foundations through a hybrid system (28 high-damping rubber bearings and 36 low-friction sliding bearings) is presented. The building incorporates a push-and-release device to evaluate its actual global dynamic response up to displacement amplitudes induced by extreme seismic events, allowing test repetitions during its service life. The testing set up and the experimental campaign, consisting of quasi-static push tests (slow loading and unloading) and push-and-release dynamic tests (slow loading and subsequent sudden release), are described. The experimental results have peculiarities related to the building (structural typology and size, foundation geometry on a steep slope, presence of the push-and-release device for future additional tests), the magnitude of the maximum horizontal displacement never achieved before (285 mm and 227 mm in the quasi-static and dynamic tests, respectively), the global and local monitored parameters (horizontal and vertical displacements, strains, accelerations, in addition to environmental conditions) providing a comprehensive insight into the behaviour of the hybrid isolation system and superstructure.

Seismic collapse probability and life cycle cost assessment of isolated structures subjected to pounding with smart hybrid isolation system using a modified fuzzy based controller

The possibility of pounding on isolated structures with surrounding moat walls is one of the concerns in the design of isolation systems, especially in pulse-type near-field earthquakes. This paper puts forward the seismic probability assessment of structures equipped with passive and smart hybrid isolation systems by considering pounding possibilities. This investigation is performed on isolated structures equipped with a high damping rubber bearing (HDRB) considering stiff moat walls around the structure. In the Hybrid isolation system, magnetorheological dampers (MR) are considered an adaptive dissipation energy device along with isolators using an optimized novel interval Type-2 fuzzy logic controller with adaptive red-zone function (IT2FS + RZF) to reduce pounding possibilities. The fragility curves of the building for various cases are determined using incremental dynamic analysis (IDA), and possible damage costs are evaluated by using exceedance probability in each damage level. This study concludes that the collapse probability of the isolated structures with restrains at the code-based distance is over the acceptable limit of ASCE 7–22. The smart additional damping system with the proposed controller reduces the possible damage cost of the building by about 64 % compared to the uncontrolled system and puts the collapse probability of the structure in the acceptable range.

Performance-Based Seismic Design of Hybrid Isolation Systems with Gap-Tunable BRBs for Bearing-Supported Bridges

This study proposes a class of hybrid isolation systems constructed by combining Buckling Restrained Braces (BRBs) with Rubber Bearings (RBs) or Lead Rubber Bearings (LRBs) for mitigating the seismic responses in bearing-supported bridges under strong earthquakes. Firstly, two different hybrid isolation systems (RB–BRB and LRB–BRB) were preliminarily designed based on the energy-conservation concept in the case of a bridge with Y-shaped piers, which can meet all the energy demands at different seismic hazard levels. Further, seismic evaluations were conducted on the bridges with the LRB, RB–BRB, and LRB–BRB isolation systems based on the nonlinear time history analyses. The proposed hybrid isolation systems show a two-phase energy dissipation behavior, which facilitates the systems to reduce the seismic responses remarkably under different earthquake scenarios and achieve most of the performance objectives corresponding to the code-specified hazard levels. Finally, based on fragility analyses, the effects of the gap spacing and the stiffness ratio of the BRB to the pier were investigated with respect to the failure probability in the case of a bridge with LRB–BRB. It has been validated that the seismic performances of this study’s bridge can be improved considerably with the optimized gap spacing and BRB stiffness.

Hybrid isolation system with wire‐rope isolators and magnetorheological dampers for the isolation of blast‐induced vibration

The aim of this research is to improve the isolation performance and energy dissipation characteristics of the widely used passive isolation (PI) system with wire-rope isolators (WRIs) under the excitation of various blast-induced vibration loads through the use of a semi-active control system. A hybrid isolation (HI) system composed of WRIs and an innovative magnetorheological (MR) damper equipped with a motion controller is proposed, which can protect sensitive equipment and nonstructural elements by attenuating their dynamic response. The designs of the MR damper's magnetic circuit and control system were validated by establishing an electromagnetic field finite element model and a motion controller simulation model, respectively. A series of quasi-static and shock table tests were conducted on models using three types of isolation: (1) a PI with WRIs, (2) an HI without a motion controller, and (3) an HI alone. The results show that the proposed MR damper can effectively restrain the tensile vibration of WRIs, significantly increase the isolation rate, and provide greater energy dissipation in HI systems with different weights of static loading subjected to various blast-induced vibration loads.

A hybrid MRE isolation system integrated with ball-screw inerter for vibration control

Magnetorheological elastomer (MRE), as a field-dependent smart material, has been widely applied on base isolation for vibration reduction. However, the MRE isolation system often experiences large drift during a strong earthquake, which may cause mechanical failure. Additionally, its performance among the low-frequency range is still limited. To tackle these problems, this paper proposes a hybrid vibration isolation system which is composed of four stiffness softening MRE isolators and a passive ball-screw inerter. A simulation was developed to prove the effectiveness of the hybrid isolation system before the earthquake tests. A scaled three-storey building was developed based on the scaling laws as the isolated objective in earthquake experiments. Besides, a linear quadratic regulation controller was utilised to control the mechanical properties of the hybrid MRE isolation system. Finally, the evaluation experiments of the building under a scaled Kobe earthquake excitation were conducted. The experimental results show that the simulation and the experimental results were in agreement, validating that the hybrid isolation system could provide a better vibration mitigation performance, in the meanwhile, reduce the displacement amplitude of the isolation system.

Hybrid geotechnical and structural seismic isolation: Shake table tests

AbstractThis paper proposes a hybrid seismic isolation system composed of geotechnical (a layer of sand or gravel as foundation soil) and structural isolation (a low‐friction foundation sliding layer), aiming to effectively improve the seismic performance of rural buildings with an economical solution. The isolation system is most suitable for low‐rise buildings in high‐seismic areas. It is also effective in colder climates as replacing sand or gravel as the foundation soil eliminates frost heave. Shake table testing of three 1/4 scale models of two‐story masonry buildings was carried out: an unreinforced brick masonry structure (model MA, without isolation), an identical structure with geotechnical isolation (model MS, with a layer of gravel as the foundation soil), and an identical structure with hybrid geotechnical and structural isolation (model MC). The dynamic characteristics and responses of the three structures were assessed and compared. Test results showed that shear failure of brick walls of model MA occurred at the first story when the input peak ground acceleration reached 0.44g. For model MS, a similar shear failure mode occurred when the acceleration reached 1.02g. Model MC relied on the layer of gravel for isolation before 0.44g, and then several cracks occurred at the foundation sliding layer, which was a sign of sliding. The plastic damage was mainly concentrated in the second story, and model MC showed bending‐dominated deformation when the acceleration increased to 1.24g. This study clearly demonstrates the improved seismic performance and technical feasibility of the cost‐effective hybrid isolation system.

Internal Pounding between Structural Parts of Seismically Isolated Buildings

ABSTRACT Pounding among internal structural parts of seismically isolated structures may happen because of high horizontal deformability of the isolation system. To study this poorly investigated issue, a reinforced concrete (r.c.) framed structure built in Sicily (Italy) is considered, with a hybrid isolation system combining elastomeric and sliding bearings. The building consists of four-storey, basement included, with the steel-framed structure of the elevator crossing the isolation level. Two structural configurations are considered for the elevator shaft: base-isolated, with rigid link to the surrounding building; fixed-base, with a seismic gap to prevent internal pounding. Effectiveness of the Italian and European code provisions, based on setting up adequate separation distance, is assessed. Four modelling assumptions of the highly nonlinear behavior of elastomeric bearings are examined and a mathematical model is calibrated on experimental data. Nonlinear seismic analysis of the test structure is carried out considering eight cases, which are obtained combining four position of the elevator (i.e., at the basement and upper three levels) and two load conditions (i.e., elevator empty and with maximum load). Torsional effects induced by an asymmetric position of the elevator shaft are quantified by means of polar plots, representing the critical envelope for all excitation angles of bi-directional earthquakes.

Magnetic damped links to reduce internal seismic pounding in base-isolated buildings

A limited gap between closely spaced structural parts may induce internal pounding in seismically isolated structures, because of notable displacement at the level of the isolation system under severe earthquakes. A gap between a fixed-base elevator shaft and the surrounding building is presented here with reference to a reinforced concrete building located in the Sicilian town of Augusta. The building, comprising a basement and three storeys above the ground level, is seismically isolated at the top of rigid columns in the basement with a hybrid isolation system including elastomeric and sliding bearings, while a steel framed elevator shaft crosses the isolation level. Despite the gap, internal pounding may occur at all levels of the superstructure when the elevator with maximum load stops at the upper floors. To reduce structural pounding effects, a magnetic damped link (MDL) between adjacent corners of the elevator and the surrounding building is proposed. This is obtained as an in parallel combination of an eddy current damped link (ECDL) and an elastic helicoidal spring, and occupies less space than traditional passive dampers and transmits considerably less forces compared to a rigid link configuration. Specifically, an ECDL consists of an outer cylindrical copper tube, as conductor, and an inner tube, equipped with an array of axially magnetized and ring-shaped permanent magnets separated by iron pole pieces, as mover. The relative motion between conductor and magnets, during seismic loading, induces an eddy current producing electromagnetic damping. Given that viscoelastic linear behaviour can be hypothesized for the MDL, a simplified iterative design procedure of the ECDL is proposed, with optimization of the thickness and radius of the magnets, thereby enhancing magnetic flux and energy dissipation. The directionality of the near-fault ground motions is investigated through nonlinear seismic analysis, comparing no connection with four configurations of the interconnection: i.e., flexible and rigid elastic links, viscous and magnetic damped links.