Hybrid Base Isolation Research Articles

Response simulation of hybrid base isolation systems under earthquake excitation

In the present work, we investigate the response of a hybrid base isolation system under earthquake excitation. The physical parameters of the hybrid base isolation system are identified from dynamic tests performed during a parallel project involving two residential buildings in the town of Solarino, Sicily, using the well-established optimization procedure ‘covariance matrix adaptation-evolution strategy’ as dynamic identification algorithm in the time domain. The base isolation system consists of high damping rubber bearings and low friction sliding bearings. Two separate models are employed for the numerical simulation of the high damping rubber bearing component, namely a bilinear system and a trilinear system, both in parallel with a linear viscous damper. In addition, a linear Coulomb friction model is used to describe the behavior of the low friction sliding bearing system. Analytical solutions are provided, in compact form, for all possible phases of motion of the hybrid base isolation system under earthquake excitation. A series of numerical simulations are carried out to highlight the behavior of the considered hybrid base isolation system under different excitation and site conditions.

Constrained optimization for 1-D dynamic and earthquake response analysis of hybrid base-isolation systems

The paper presents a constrained optimization procedure (COP) for the dynamic analysis of hybrid base isolation systems under earthquake excitation. After a description of the hybrid system considered, the mechanical model used for its representation is introduced, along with the governing equations. Mid-point central difference time-discretization is used to cast the computations in each time increment as a quadratic optimization problem with non-linear constraints. Numerical applications illustrate the accuracy and robustness of the formulation and highlight some typical performance characteristics of hybrid base isolation systems.

Seismic Analysis and Comparison of Different Base Isolation Systems for a Multi-Storey RC Building with Irregularities in Plan

In the present paper the dynamic nonlinear analysis for a 3D base isolated structure is illustrated. A base isolated reinforced concrete building is designed and verified according to the European seismic codes such that the superstructure remains almost completely elastic and the nonlinear elements are localized only in the base isolation system. Nonlinear hysteretic models have been adopted to reproduce the cyclic behavior of the isolators. Two different base isolation systems are considered and their performances are compared for evaluating the behaviour of a base isolated building, highly irregular in plan, in presence of a seismic excitation defined with recorded accelerograms which characterize the bi-directional ground motions. The isolation system has been realized with a combination in parallel of elastomeric bearings and sliding devices. In the first analyzed isolation system we have used the High Damping Rubber Bearings (HDRB) and in the second analyzed isolation system we have used the Lead Rubber Bearings (LRB). Finally a comparative analysis between the base isolated structure with hybrid base isolation systems and the conventional fixed base structure is detailed.

Dynamic Nonlinear Analysis of an Hybrid Base Isolation System with Viscous Dampers and Friction Sliders in Parallel

In the present work we have analyzed a particular base isolation system for the seismic protection of a multi-storey reinforced concrete (RC) building. The viscous dampers and friction sliders are the devices adopted in parallel for realizing the base isolation system. The base isolation structure has been designed and verified according to European seismic code EC8 and by considering for the friction sliders the influence of the sliding velocity on the value of the friction coefficient. A dynamic nonlinear analysis for a three-dimensional base isolated structure has been performed. Recorded accelerograms for bi-directional ground motions have been used which comply with the requirements imposed by EC8 for the representation of a seismic action in a time history analysis. In this paper a comparative analysis is presented between the base isolated structure with the described hybrid base isolation system and the traditional fixed base structure.

Hybrid Base Isolation System with Friction Sliders and Viscous Dampers in Parallel: Comparative Dynamic Nonlinear Analysis with Traditional Fixed Base Structure

In the present paper we have analyzed a multi-storey reinforced concrete (RC) building in presence of a hybrid seismic protection system for highlighting the limits of the conventional fixed base seismic design of structures. This hybrid seismic protection system is a passive structural control system that combines the Base Isolation System (BIS) and the Passive Supplemental Damping (PSD). The Viscous Dampers (VS) and Friction Sliders (FS) are the devices adopted in parallel for realizing the innovative base isolation system. The fixed base structure and the base isolated structure have been designed and verified according to the European seismic code EC8 and the European code for the design of concrete structures EC2. A three-dimensional dynamic nonlinear analysis for a base isolated structure has been performed adopting recorded accelerograms for the defined bi-directional ground motions according to the conditions imposed by EC8. The seismic isolation is a promising alternative for the earthquake resistant design of buildings and its peculiarity is that the base isolated buildings are designed such that the superstructure remains elastic and the nonlinearities are localized at the isolation level. In this paper a comparative analysis is presented between the base isolated structure, with the viscous dampers in parallel with friction sliders, and the traditional fixed-base structure.

Analytical earthquake response of 1D hybrid base isolation systems

The work presents several dynamic analyses of an actual base isolation system previously identified by using a non-linear 1D model and full scale free vibration tests. After a short introduction to the building and the base isolation system considered, reference is made to previous studies where the model used was developed. The analytical model, originally derived for free vibration analyses and system identification applications, is extended in the present paper to earthquake response simulations. First a theoretical harmonic ground motion is considered, in order to identify resonance conditions for the system and stress how these should be avoided in actual design, by carefully studying the seismological and site conditions. The response of the system to a nearly harmonic natural ground motion is then predicted. Next the performance of the system under several significant ground motions from the Friuli 1976, Irpinia 1980 and L'Aquila 2009 earthquakes is considered, and the reasons for its satisfactory or unsatisfactory behaviour are pointed out and explained. Means for correcting unsatisfactory performances are also suggested and discussed. The behaviour of the system under near fault records from the L'Aquila 2009 earthquake is then considered, the conditions leading to the maximum demands are highlighted and the reasons behind them are clearly explained. Finally the 1D model presented is used to predict the 2D response to 2D ground motions.

Base‐isolated structures with selective controlled semi‐active friction dampers

AbstractThis paper investigates effectiveness of selective control strategy in hybrid base isolation systems including isolators and semi‐active variable friction (VF) dampers. According the selective control strategy, VF dampers are activated just if the displacement at the isolators exceeds the threshold value. The slip‐force control is based on the values of floors' accelerations and velocities. By controlling the slip‐force magnitude in the VF dampers, effective energy dissipation can be achieved in a seismic event. Activation of dampers according to the selective control strategy allows high‐energy dissipation by minimum energy required for adjusting the slip‐force. Performance of a multi‐storey frame with a base isolation system and VF dampers under various earthquake records was obtained numerically using originally developed MATLAB routines. Seismic response of the analysed structure with the selective controlled system was compared with that when the VF dampers were active during the whole earthquake. It is shown that adjustment of the slip‐force in a selective manner allows additional reductions in peak displacements and accelerations of the structure. The results also demonstrate that this control strategy yields reduction of the base displacement without increasing the peak base shear forces. Copyright © 2009 John Wiley & Sons, Ltd.

Superelastic semi-active damping of a base-isolated structure

A hybrid base isolation system that is composed of linear elastomeric bearings (EB), friction-pendulum bearings (FPB), shape memory alloy (SMA) wires, and magnetorheological (MR) dampers is proposed for the mitigation of seismic motions. Each subcomponent of the isolation system is employed for a unique task in managing superstructure response when ground motions are experienced. EB are provided to couple the superstructure and substructure in the vertical direction while partially decoupling the superstructure from lateral ground motion. FPB provide support for gravity loads and a restoring force when base drifts become large. SMA wires supply recoverable hysteretic behavior and serve as an additional restoring force. Finally, MR dampers provide variable viscous damping that can be altered in real time for intelligent amelioration of superstructure response. Neuro-fuzzy techniques are incorporated to model SMA and MR elements. A fuzzy logic controller is generated using a multi-objective genetic algorithm for optimal modulation of MR damper resistance levels. To evaluate performance of the proposed isolation system the Phase II, Part IV Base Isolation Benchmark Problem is adopted and standard performance metrics are considered. The nominal isolation system of the problem statement is augmented with SMA and MR devices. Hysteretic behavior of each device is analyzed and their complimentary behavior is identified. Results of several control cases are provided that include semi-active and passive operation of the MR dampers and several configurations of SMA wires. Results show that the proposed superelastic semi-active base isolation system can reduce base drifts by 18% and maintain favorable superstructure response. Copyright © 2008 John Wiley & Sons, Ltd.

Hybrid base-isolation with magnetorheological damper and fuzzy control

A series of large-scale experimental tests is conducted on a mass equipped with a base-isolation system that consists of high damping rubber bearings (HDRB) and a 300 kN magnetorheological (MR) damper. The 21 772 kg mass and its hybrid isolation system are subjected to various intensities of near- and far-fault earthquakes on a large shake table. Three proposed fuzzy controllers use feedback from displacement, velocity, or acceleration transducers attached to the structure to modulate resistance of the semi-active damper to motion. Results from various types of passive and semi-active control strategies are summarized and compared. The study shows that a combination of HDRB isolators and an adjustable MR damper can provide robust control of vibration for large civil engineering structures that need protection from a wide range of seismic events. Low power consumption, direct feedback, high reliability, energy dissipation, and fail-safe operation are validated in this study. Copyright © 2006 John Wiley & Sons, Ltd.

Neuro-fuzzy model of hybrid semi-active base isolation system with FPS bearings and an MR damper

Full-scale experiments are carried out on a single-degree-of-freedom mass that is equipped with a hybrid base isolation system. The isolator consists of a set of four friction pendulum system (FPS) bearings and a magnetorheological (MR) damper. The 13,620 kg mass and its hybrid isolation system are subjected to various intensities of near- and far-fault earthquakes on a large shake table. The proposed fuzzy controller uses feedback from displacement or acceleration transducers attached to the structure to modulate resistance of the semi-active damper to motion. Results from several types of passive and semi-active control strategies are summarized and compared. The study shows that a combination of FPS bearings and an adjustable MR damper can provide robust control of vibration for a large full-scale structure undergoing a wide variety of seismic loads. Low power consumption, real-time feedback control, and fail-safe operation are validated in this study. A combination of the FPS bearings and the MR damper appears to offer significant possibilities for reduction of displacement and acceleration due to seismic load. A neuro-fuzzy model is used to represent behavior of the damper for various displacement, velocity, and voltage combinations that are obtained from a series of laboratory evaluation tests. Modeling of the FPS bearings is carried out with a nonlinear analytical equation and neuro-fuzzy training. Numerical simulation using neuro-fuzzy models of the MR damper and FPS bearings predict the response of the hybrid base isolation system very well. Results show that dynamic behavior of the FPS bearings and MR damper can be successfully estimated using these neuro-fuzzy models.

A design approach for semi-active and smart base-isolated buildings

Hybrid isolation systems consisting of mainly a base isolation system and either active controllers or semi-active dampers or smart dampers or combination thereof for protecting buildings from seismic damage can make further improvements on isolation performance. The control forces in active controllers of hybrid isolation systems are analyzed and the damping characteristics of control forces in active controllers are then observed. Two indices are defined to quantify the damping characteristics of control force in active controllers. Based on the observation of damping characteristics of control forces in active controllers, a design approach for semi-active, smart and even passive dampers in a hybrid isolation system is presented. For comparative design purposes, the average value of maximum control forces in active controllers and control devices to be designed for several excitation records are assumed to be the same, i.e. the control design is normalization. A five-storey building and the smart base-isolated benchmark building are employed as numerical studies. The simulation results demonstrate that smart base isolation systems designed by using the proposed design approach can achieve almost the same performance as an active base isolation system in protecting the safety of buildings against strong earthquakes. Additionally, active controllers or semi-active controllers in hybrid base isolation system present the behavior of passive devices. And thus passive devices in base isolation systems can be instead of active controllers or semi-active controllers with the performance of the base isolation system remaining. Copyright © 2005 John Wiley & Sons, Ltd.

MR 감쇠기와 FPS를 이용한 하이브리드 면진장치의 수치해석적 연구

본 연구에서는 하이브리드 면진장치가 설치된 단자유도 구조물의 동적거동을 예측할 수 있는 수치해석모델을 제안한다. 하이브리드 면진장치는 MR 감쇠기와 마찰진자시스템(FPS)으로 구성된다. MR감쇠기의 동적거동을 모형화하기 위하여 뉴로-퍼지 모델을 사용한다. 다양한 변위, 속도, 전압의 조합을 사용하여 MR 감쇠기의 성능실험을 수행한 후 얻어진 데이터를 이용하여 MR 감쇠기 뉴로-퍼지 모델을 ANFIS로 학습시킨다. FPS의 모형화는 본 연구에서 유도한 비선형 모델식에 근거하여 뉴로-퍼지 모형화방법을 사용하여 이루어진다. 본 연구에서는 MR 감쇠기로 전달되는 제어전압을 조절하기 위하여 퍼지논리제어기를 사용한다. 다양한 지진하중을 사용한 진동대 실험을 통하여 얻은 실험체의 동적응답과와 뉴로-퍼지 모형화방법을 사용한 수치해석의 결과를 비교한다. 뉴로-퍼지 모델을 사용하여 MR 감쇠기와 FPS를 모형화해서 수치해석을 수행한 결과 하이브리드 면진장치의 동적거동을 매우 정확하게 예측할 수 있었다. Numerical analysis model is proposed to predict the dynamic behavior of a single-degree-of-freedom structure that is equipped with hybrid base isolation system. Hybrid base isolation system is composed of friction pendulum systems (FPS) and a magnetorheological (MR) damper. A neuro-fuzzy model is used to represent dynamic behavior of the MR damper. Fuzzy model of the MR damper is trained by ANFIS (Adaptive Neuro-Fuzzy Inference System) using various displacement, velocity, and voltage combinations that are obtained from a series of performance tests. Modelling of the FPS is carried out with a nonlinear analytical equation that is derived in this study and neuro-fuzzy training. Fuzzy logic controller is employed to control the command voltage that is sent to MR damper. The dynamic responses of experimental structure subjected to various earthquake excitations are compared with numerically simulated results using neuro-fuzzy modeling method. Numerical simulation using neuro-fuzzy models of the MR damper and FPS predict response of the hybrid base isolation system very well.

MR 감쇠기와 FPS를 이용한 하이브리드 면진장치의 퍼지제어

본 연구에서는 하이브리드 면진장치가 설치된 단자유도 구조물에 대하여 진동대 실험을 수행하였다. 본 연구에서 사용된 하이브리드 면진장치는 네 개의 FPS와 한 개의 MR 감쇠기로 구성하였다. 다양한 크기 및 특성을 가진 지진하중을 하이브리드 면진장치가 설치된 구조물에 가하여 진동제어 성능을 평가하였다. 본 연구에는 준능동 MR 감쇠기의 저항력을 효과적으로 조절하기 위하여 퍼지제어기를 사용하였고 구조물에 부착된 계측기를 통하여 변위 및 가속도를 피드백으로 이용한다. 수동 및 준능동 제어기법을 사용하여 얻은 구조물의 응답을 서로 비교하였고 그 결과 FPS와 MR 감쇠기의 조합으로 다양한 특성의 하중을 받는 구조물의 진동제어를 효과적으로 수행할 수 있음을 알 수 있다. Shaking table tests are carried out on a single-degree-of-freedom mass that is equipped with a hybrid base isolation system. The isolator consists of a set of four specially-designed friction pendulum systems (FPS) and a magnetorheological (MR) damper. The structure and its hybrid isolation system are subjected to various intensities of near- and far-fault earthquakes on a large shake table. The proposed fuzzy controller uses feedback from displacement or acceleration transducers attached to the structure to modulate resistance of the semi-active damper to motion. Results from several types of passive and semi-active control strategies are summarized and compared. The study shows that a combination of FPS isolators and an adjustable MR damper can effectively provide robust control of vibration for a large full-scale structure undergoing a wide variety of seismic loads.

사장교를 위한 LRB-기반 복합 기초격리 시스템

사장교에 발생하는 지진에 의한 진동을 감소시키기 위해 추가적인 능동/반능동 제어장치를 부착한 LRB-기반 복합 기초격리 시스템에 대한 논문이다. 복합 기초격리 시스템은 제어장치가 다중으로 작동하기 때문에 LRB가 설치된 교량 시스템과 같은 수동형 기초격리 시스템에 비해 제어 성능이 뛰어나다. 본 논문에서는, LQG 알고리듬에 의해 제어되는 능동형 유압식 가력기와 clipped 최적제어에 의해 제어되는 반능동형 자기유변 유체 (MR) 감쇠기를 추가적인 제어장치로 고려하여 추가적인 응답 감소 효과를 검토하였다. 이를 위해, 미국토목학회의 1단계 벤치마크 사장교에 LRB를 설치한 교량을 고려하였다. 수치해석 결과를 통해, 모든 LRB-기반 복합 기초격리시스템이 구조물의 응답을 효과적으로 감소시킴을 확인하였다. 또한, MR 감쇠기를 채택한 복합 기초격리 시스템은 구조물 강성의 불확실성에 대해 강인성을 보였지만 유압식 가력기를 채택한 경우에는 강인성이 부족함을 알 수 있었다. 따라서, 반능동형 추가 제어장치를 채택한 복합 기초격리 시스템의 대형 토목구조물에 대한 적용가능성이 제어 성능 및 강인성 면에서 분명하게 검증되었다. This paper presents LRB-based hybrid base isolation systems employing additional active/semiactive control devices for mitigating earthquake-induced vibration of a cable-stayed 29 bridge. Hybrid base isolation systems could improve the control performance compared with the passive type-base isolation system such as LRB-installed bridge system due to multiple control devices are operating. In this paper, the additional response reduction by the two typical additional control devices, such as active type hydraulic actuators controlled by LQG algorithm and semiactive-type magnetorheological dampers controlled by clipped-optimal algorithm, have been evaluated bypreliminarily investigating the slightly modified version of the ASCE phase I benchmark cable-stayed bridge problem (i.e., the installation of LRBs to the nominal cable-stayed bridge model of the problem). It shows from the numerical simulation results that all the LRB based hybrid seismic isolation systems considered are quite effective to mitigate the structural responses. In addition, the numerical results demonstrate that the LRB based hybrid seismic isolation systems employing MR dampers have the robustness to some degree of the stiffness uncertainty of in the structure, whereas the hybrid system employing hydraulic actuators does not. Therefore, the feasibility of the hybrid base isolation systems employing semiactive additional control devices could be more appropriate in realfor full-scale civil infrastructure applications is clearly verified due to their efficacy and robustness.

Protective systems for high-technology facilities against microvibration and earthquake

Microvibration of high technology facilities, such as semiconductor plants and facilities with high precision equipments, due to nearby road and rail traffic has attracted considerable attention recently. In this paper, a preliminary study is conducted for the possible use of various protective systems and their performance for the reduction of microvibration. Simulation results indicate that passive base isolation systems, hybrid base isolation systems, passive floor isolation systems, and hybrid floor isolation systems are quite effective and practical. In particular, the performances of hybrid floor isolation systems are remarkable. Further, passive energy dissipation systems are not effective for the reduction of microvibration. Finally, the protections against both microvibration and earthquake are also investigated and presented.

Seismic response variability of hybrid-controlled bridges

The present author, collaborating with others, developed earlier a prototype hybrid base isolation system using friction-controllable sliding bearings and demonstrated its effectiveness in circumventing the shortcomings of passive counterparts by means of shaking table tests and numerical analysis under the 1940 El Centro earthquake record linearly scaled to various levels of intensity. The purpose of the present paper is to show that the same hybrid system exhibits a similar degree of effectiveness over a practical range of parameters that define the ground acceleration characteristics. These parameters include spectral shape, dominant frequency, and duration of the ground motion. For this purpose, artificial earthquake ground acceleration histories representing different sets of these parameter values are generated using a modified Kanai-Tajimi spectrum. The bridge responses under these earthquakes are evaluated numerically when the bridge is isolated by passive and hybrid sliding systems. The results demonstrate that the hybrid system indeed more effectively isolates the bridge under a variety of ground motion characteristics.