Semi-active Base Isolation System Research Articles

Uncertainty in the seismic performance of semi-active base isolation systems

In a conventional base isolation system, minimizing the seismic responses of the superstructure is always at the cost of increasing the isolator's response. The semi-active control of the isolator has been considered an effective solution to such a dilemma. It tunes the real-time properties of the isolator according to preset rules to further reduce the superstructure's seismic responses without increasing that of the isolator or vice versa. However, the number of ground motion records used to design and validate the controller, i.e., the preset rules, in existing studies is usually very small and therefore is suspectable if it is adequate to address the significant uncertainty in the shaking of future earthquakes. This paper critically reviews the performance of the proportional-integral-derivative (PID), linear-quadratic regulator (LQR), and fuzzy controllers in semi-active base isolation systems with magnetorheological (MR) dampers subjected to highly uncertain ground motion inputs through numerical simulations. The results show that the control performance of the controllers varies significantly with the increasing number of input records, suggesting the necessity of using at least 50 ground motion records to appropriately assess the performance uncertainty of semi-active base isolation systems. More importantly, the superior performance of the optimized controllers is not guaranteed if the system is subjected to ground motions that are new to the controller, even if the controller has been optimized for thousands of existing ground motions. It highlights the need of improving the adaptability of the semi-active systems for uncertain ground motion inputs.

Modified H2/LQG control algorithm for designing a multi-objective semi-active base isolation system

This paper proposes a modified version of H2/Linear Quadratic Gaussian (H2/LQG) control algorithm (MH2/LQG) to design effective semi-active base isolation systems with a supplemental magneto-rheological (MR) damper for simultaneously controlling the base drift and acceleration of a structure. In the proposed MH2/LQG control algorithm, the weighting parameter defined in the semi-active control law is considered variable during the seismic loading and is adjusted at each time step to prevent the device from applying excessive damping force to the structure. As a result, the supplemental control system is designed not only to reduce the base drift of the isolated structure but also to restrict increases that may occur in accelerations imparted to the superstructure due to excessive damping forces. As a numerical example to illustrate the proposed method, an isolated four-story structure is subjected to different earthquake records and the semi-active base isolation system is designed using both H2/LQG and MH2/LQG control algorithms. The results show the effectiveness of the proposed MH2/LQG control algorithm in designing semi-active base isolation systems which can provide a proper simultaneous control of the base drift and floor accelerations. In addition, comparing the performance of the MH2/LQG and multi-objective H2/LQG control algorithms shows that while the two design procedures work similarly in mitigating the maximum base drift, the MH2/LQG control algorithm is more effective in reducing the maximum floor acceleration.

Effective Semiactive Base Isolation System under Multiple Earthquakes

A method is proposed to design an effective semiactive control system composed of a linear low damping base isolation and a supplemental magnetorheological (MR) damper when the structure subjected to multiple earthquakes. In the proposed design method, the parameters of semiactive control system have been determined based on minimizing the average of maximum response of isolated structure under multiple design ground motions. To select appropriate value for force related weighting parameter, defined in performance index, a range has been suggested for each design objective. For numerical simulations, a scaled three-story base-isolated frame subjected to different scaled real earthquakes as well as filtered white noise excitations and the proposed method has been applied to design semiactive base isolation system under multiple earthquakes. The results of numerical simulations have shown the capability of the proposed method in designing an effective semiactive base isolation system, the performance of which under multiple earthquakes has been almost close to the case that it is designed optimally for each earthquake separately. Also, under multiple earthquakes, using the passive-off and passive-on forms of MR damper can be recommended, respectively, regarding to the objectives of minimizing the maximum acceleration and base drift.

Performance of Semi-Active Base Isolation Systems under External Explosion

Structures designed against earthquake loads based on using control systems may experience explosions during their lifetime. In this paper, the performance of a hybrid control system composed of a low-damping base isolation and a supplemental magneto-rheological (MR) damper under external explosion has been studied. Base isolation system has the ability of decreasing the maximum structural response under blast loadings by shifting the period of the structure. In addition, MR damper improves the base isolation system performance by controlling the base drift of the structure. Hence, in this paper, the capability of a hybrid base isolation system equipped with an MR damper at the base has been evaluated in reducing the maximum structural response and base drift under external blast loadings. To determine the voltage of the semi-active MR damper, the H2/Linear Quadratic Gaussian (LQG) and clipped-optimal control algorithms have been applied. For numerical simulations, a 10-storey shear frame subjected to blast loadings applied on different floors has been considered and the performance of the hybrid isolation system and MR damper has been studied. The results have proven the effectiveness of the hybrid control system in controlling the maximum response and base drift of the isolated structure against spherical external explosion. Furthermore, comparing the performance of the hybrid passive and semi-active base isolation systems indicates that the semi-active hybrid base isolation system is more effective in reducing the root-mean-square (RMS) value of the base drift. Similarly, it has been found that the semi-active hybrid base isolation system also performs better than the high-damping base isolation system.

Effect of various factors on the design of control algorithm of semi-active base isolation systems

In this article, the effect of various factors, such as earthquake characteristics, base isolation system properties, and dynamic model of isolated structure, on the design of control algorithm of ...

Optimal Response-Related Weighting Matrices to Control Semi-Active Base Isolation Systems

Abstract In this paper, the performance of a semi-active base isolation system, including a magneto-rheological (MR) damper and base isolation system for different combinations of response-related weighting matrices, has been studied. To consider all possible sets of response-related matrices, seven H2/linear quadratic Gaussian (LQG) control designs have been considered. For a numerical simulation, a six-story shear frame has been subjected to different earthquakes, and the performance of the control system has been evaluated. The results show that the optimal force-related weighting parameter is identical for different sets of response-related weighting matrices and is also independent of earthquake records when minimizing the maximum base drift is considered as the design objective. Also, the results of different sets of response-related weighting matrices show that the optimal sets for the design objective of minimizing the maximum base drift are the velocity and displacement/velocity-related weighting matrices.

Seismic Response Reduction in Liquid Storage Tanks by Simple Smart Base Isolation Systems

In this paper, a nonlinear autonomous algorithm is proposed to control the variable dampers and to provide semi-active control of a liquid storage tank by taking advantage of similarity to friction models and avoiding demerits. Friction mechanism in sliding bearings shows rigid-perfectly plastic behavior with limited damping force. However, transition of vibrations of high frequencies and appearance of residual displacements after the excitation are the drawbacks of such systems. Considering a performance-based seismic design approach, the proposed damping mechanism is capable of controlling the system in a two-level seismic design criterion. The performance and applicability of both the proposed algorithm and a variable oil damper under this command were experimentally verified in previous research. The effect of passive and semi-active seismic control of a liquid storage tank on the response of the structure and sloshing liquid is analytically investigated. Three base isolation systems with passive viscous or sliding dampers are applied and compared with three hybrid semi-active base isolation systems. Pseudo-negative stiffness, skyhook and a proposed control strategy by author are utilized as the control systems. A lumped mass–spring model is employed to represent the dynamic behavior of the tank and the contained liquid. The structural response and sloshing are calculated and compared. It is shown that the smart base isolation system is effective in reduction in the base shear and displacement of the structure. The sloshing response observed through the displacement and kinetic energy of the convective mass is reduced by the hybrid control systems.

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.

자기민감 고무를 이용한 구조물의 면진성능 연구

최근 들어 지진발생 빈도의 증가와 더불어 초고층 빌딩, 장대교량 등과 같은 대형구조물의 경량화, 유연화로 인해 발생하는 구조물의 과도한 동적거동을 효과적으로 제어할 수 있는 제진시스템의 필요성이 증가하고 있다. 본 연구에서는 지진으로부터 구조물을 보다 효과적으로 보호하기 위해 자기장에 의해 역학적 성질을 변화시킬 수 있는 제어가 가능한 지능형재료인 자기민감 고무(Magneto-Sensitive Rubber)를 이용한 반 능동 기초격리 시스템을 제안하였다. 제안된 기초격리 시스템은 기존의 LRB(Lead-Rubber Bearing) 시스템과의 비교 분석을 통해 면진성능을 평가하였으며 이를 위해 몇 가지 역사적 지진들을 이용수치해석을 수행하였다. 제안된 자기민감 고무를 이용한 반 능동 기초격린 시스템은 기존의 수동 시스템보다 기초전단력이나 상부구조물에 가속도 전달을 차단함과 동시에 기초변위를 현저하게 감소시킬 수 있음을 보였다. 그러므로 자가민감 고무를 이용한 반 능동 기초격리 시스템은 지진으로부터 구조물을 효과적으로 보호할 수 있을 것으로 사료된다. Recently, as large structures such as high-rise building and long span bridge become lighter and more flexible, the necessity of structural control for reducing excessive dynamic response due to seismic excitation is increased. In this study, a semi-active base isolation system using Magneto-Sensitive (MS) rubbers is proposed to effectively protect structures against earthquakes. MS Rubber is a class of smart controllable materials whose mechanical properties change instantly by the application of a magnetic field. To demonstrate the performance of this device, the MS Rubber isolation system is compared to Lead-Rubber Bearing (LRB) isolation systems and judged based on computed responses to several historical earthquakes. The MS Rubber isolation system is shown to achieve notable decreases in base drifts over comparable passive systems with no accompanying increase in base shears or in accelerations imparted to the superstructure. The proposed MS Rubber system is shown to perform better than the passive isolation system.

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.

Effect of high-frequency low-amplitude vibration on the performance of a class of semi-active base isolation systems with on–off damping

An alternative vibration isolator that incorporates on–off friction damper with fast excitation input at the base of the damper is proposed in this paper. Friction is modelled using the Coulomb's friction model as well as the LuGre model. Analytical expressions are obtained for the effective damper performance under fast excitation, and the performance of the isolator is studied in light of the effective damping characteristics. Numerical simulation of equation of motion validates the analytical results.