Smart Base Isolation System Research Articles

RL-based Control of Smart Base Isolation System Using Unity ML-Agents

RL-based Control of Smart Base Isolation System Using Unity ML-Agents

Dynamic behavior modelling of a hybrid magnetorheological elastomer with encapsulated fluid for base vibration isolation

Magnetorheological elastomers (MRE) based semi-active isolators utilize MREs whose mechanical properties, such as stiffness and damping, change in response to an external magnetic field. MREs implementation in semi-active isolation remains challenging due to their slow response time caused by the suspension of the magnetic particles inside the elastomeric matrix and limited damping capabilities. Hybrid MREs, a combination of MREs and MRFs, have been developed to improve semi-active isolation's material properties and performance. However, modelling the nonlinear and hysteretic behavior of hybrid MRE-based isolators remains a challenge and needs to be adequately addressed. To bridge the gap, this study presents a parametric model for a hybrid semi-active isolator's nonlinear and hysteretic behavior that utilizes a hybrid MRE (H-MRE). The behavior of conventional and hybrid MRE-based isolators are experimentally tested under varying loading conditions of excitation frequency and input current. Simulation models are created using combinations of three different phenomenological models, Bouc-Wen, Modified-Dahl and LuGre friction. The experimental data are used to optimize and fit the simulated response of each model, and hence optimal values of the MRE and MRF hysteresis parameters are determined. The parameter estimation results indicate that a combination of LuGre friction for the MRE and Bouc-Wen for the MRF improves the accuracy of predicting the dynamic behaviour of the hybrid isolator. The relationship between the model parameters and loading conditions is also investigated and described through polynomial equations of the third order. These findings could provide valuable insights for the system identification and control of hybrid semi-active isolators and pave the way for developing smart base isolation systems utilizing hybrid MREs in future research.

A frequency-dependent variable-damping control based variable-orifice damper for smart base-isolation system

Damping devices are commonly used in the isolation layer of base-isolated structures to provide additional damping to control the structural responses. Normally, large damping for the isolation layer is useful to minimize the resonance effect under low-frequency ground motions, and small damping is preferred to reduce the structural responses under high-frequency ground motions. Traditional passive dampers are widely adopted in engineering practice. Due to the fixed damping characteristic, however, the performance of base-isolated structures with passive dampers cannot stay optimal under ground motions with different frequency characteristics. To realize an optimal control of base-isolated structures, semi-active control has been increasingly valued for its efficiency and intelligence to adjust the damping characteristics based on feedback information from the structure and ground motion. However, a large number of sensors and hardware components are required for semi-active control, which makes the system complex and costly. In this paper, a variable-orifice damper (VOD) for smart base-isolation system is proposed. The VOD can adaptably adjust its damping according to the frequency of the ground motion without additional power or sensors. Theoretical analysis and sinusoidal excitation tests were carried out to investigate the behavior of VOD. A series of numerical simulations of a base‐isolated structure equipped with the proposed VOD and subjected to ground motions are also conducted. A semi-active control with ON-OFF strategy, and two passive controls (passive-on and passive-off) are conducted for comparison. The simulation results show that the VOD can result in an optimal control under ground motions with different frequency characteristics.

Seismic Response Mitigation of Extra-Large LNG Storage Tanks

The paper investigates the effectiveness of a smart base-isolation system for seismic response mitigation of extra-large liquified natural gas (LNG) storage tanks. The mathematical model of the base-isolated LNG tank with smart dampers, the magneto-rheological (MR) dampers, is presented. The governing equations of motion of the smart system are derived and solved by the classical transition matrix method in the time domain. The linear quadratic regulator (LQR) control scheme is employed to command MR dampers. The LNG tank system is analyzed under six artificial accelerograms, compatible with operational basis earthquake (OBE) and safe shutdown earthquake (SSE) response spectrum, generated using a method of a random set of phase angles with amplitudes obtained from power spectral density function. A time-delay compensation procedure based on the Taylor series expansion is applied to reduce the deterioration of control performance due to time delay. To investigate the effectiveness of smart base-isolation, the responses are compared with the fixed-base tank, base-isolated tank, and tank with passive MR damper. The results show that the smart base-isolation is effective in reducing the seismic response of extra-large LNG tanks, especially the displacement at the isolation level without much altering other responses. The passive MR damper is also found effective and showed fail-safe behavior even under the failure of the control algorithm. Moreover, the application of time-delay compensation using the Taylor series increased the performance and overall efficiency of the LNG tank system.

Investigation of the Structural Response of the MRE-Based MDOF Isolated Structure under Historic Near- and Far-Fault Earthquake Loadings

Fixed base structures subjected to earthquake forces are prone to various issues, such as the attraction of greater forces to structure, amplified accelerations to non-structural components, expensive design for better seismic performance, and so forth. Base isolation applied at the foundation of vulnerable structures is a radical bypass from the conventional approaches utilized by structural engineers. However, the practical implementation of passive base isolation is constrained by factors such as large displacements at isolation level, uplifting forces at isolators, and vulnerability to unpredictable and versatile earthquakes. This study is focused on the evaluation of the smart base isolation system under various harmonic and earthquake loadings. The proposed system employs a magnetorheological elastomer (MRE)—a class of smart materials, based on an adaptive isolation layer under the building structure for its vibration control. The building is idealized as a five-degree-of-freedom (DOF) structure with the mass lumped at each storey. The stiffness of the MRE isolation layer is adjusted using the linear quadratic regulator (LQR) optimal feedback control algorithm. A total of 18 simulations have been performed for the fixed base, passively isolated, and MRE-based isolated structures under a series of earthquake loadings of both a near-fault and far-fault nature for analyzing a total of 306 responses of the structures. The simulation results indicate that MRE-based isolation has significantly reduced all the responses compared to the passively isolated structure for both the near-fault and far-fault earthquake loadings. For harmonic loading, however, the passively isolated structure outperformed the MRE isolated structure in terms of storey drift and acceleration responses.

Optimal Placement of Sensors for Controlling Smart Base Isolation Systems

Smart base isolation composed of a low-damping base isolation and a supplemental magneto-rheological (MR) damper is one of the most effective semi-active control systems to protect the structures against earthquake. In this study, optimal placement of sensors is determined by using a mixed-integer genetic algorithm for best possible performance. The results show significant effect of sensor configuration on the control system performance, revealing that the sensor configuration should be taken as an important factor in design process of smart base isolation. Besides, although optimal determination of sensor placement improves the control system performance, a high number of sensors is needed to measure structure responses. A method using the least number of sensors is proposed in order to reduce the control cost. The results show the effectiveness of this method in achieving near-optimal response and reducing the control cost.

An adaptive control algorithm for smart base isolation systems based on seismic early warning system

The common control strategy of smart base isolation composed of a low-damping rubber bearing and a magneto-rheological (MR) damper is to use MR damper in semi-active form. One drawback of this strategy is increasing the acceleration of isolated structure due to adding MR damper, especially under low-intensity earthquakes. This paper proposes a new adaptive-passive control approach for smart base isolation system. In this approach, MR damper performs in passive form while its behaviour is adjusted proportionally to intensity of the incoming earthquake which can be provided by a seismic early warning system (SEWS). For comparison purposes, hybrid control system has been also designed using the common control strategy in semi-active form. Because of the lack of high accuracy of SEWS in predicting the earthquake intensity, the performance of proposed control approach has been evaluated for an error of 20% in the estimated earthquake intensity. Evaluation of the performance of these control strategies under testing earthquake records shows that adaptive-passive control algorithm works better than semi-active control algorithm in controlling the seismic response of structure and the proposed control algorithm has effective performance under a wide range of earthquake intensities.

Design issues for smart isolation of structures: past and recent research

The paper focuses on a number of original researches developed by the authors concerned with the development of new design approaches for smart base isolation systems for structures. Base Isolation (BI) systems represent the first kind of control devices applied to civil structures. In the paper, advancement in technology is exploited in this field, allowing to conceive new BI typologies possibly based on the adoption of special smart materials or on the coupling of the basic passive device with additional corrective devices, in such a way to minimize the disadvantages deriving from the simply passive system. Illustrated procedures also embed in the design pattern of base-isolation systems the interaction effects between structure and soil in order to provide the best tuning of the isolation parameters and to get the maximum performance of the devices, finally summarizing a number of original approaches to design under passive, semi-active and hybrid modes.

Effects of Shape Memory Alloys on Response of Steel Structural Buildings within Near Field Earthquakes Zone

Base isolation is one of the effective ways for controlling civil engineering structures in seismic zone which can reduce seismic demand. Also is an efficient passive control mechanism that protects its superstructure during an earthquake. However, residual displacement of base-isolation systems, resulting from strong ground motions, remain as the main obstacle in such system’s serviceability after the earthquake. Shape Memory Alloys (SMA) is amongst the newly introduced smart materials that can undergo large nonlinear deformations with considerable dissipation of energy without having any permanent displacement afterward. This property of SMA may be utilized for designing of base isolation system to increase the structure’s serviceability. Here, a proposed semi-active isolation system combines laminated rubber bearing system with shape memory alloy, to take advantage of SMAs high elastic strain range, in order to reduce residual displacements of the laminated rubber bearing. Merits of the system are demonstrated by comparing it to common laminated rubber bearing isolation systems. It is found that the optimal application of SMAs in base-isolation systems can significantly reduce bearings’ residual displacements. In this study, OpenSees program for a three dimensional six-storey steel frame building has been used by locating the isolators under the columns for investigating the feasibility of smart base isolation systems, i.e., the combination of traditional Laminated Rubber Bearing (LRB) with the SMA, in reducing the structure’s isolated-base response to near field earthquake records are examined. Also, a new configuration of SMAs in conjunction with LRB is considered which make the system easier to operate and maintain.

Earthquake early warning-enabled smart base isolation system

Recent deployments of Earthquake Early Warning (EEW) system in Japan and some other earthquake-prone regions provide the vital warning signals prior to the arrival of destructive ground motions. The EEW system uses the different traveling speed of seismic P- and S-waves to achieve the goal of earthquake warning. This technology is primarily used to produce warning signals to alert the public to avoid potential risks, such as to evacuate from buildings. It is also used to mitigate other risks such as reducing train speed of Shinkansen trains. The present study suggests a new seismic-risk mitigation technique by connecting a base isolation system with the EEW. Base isolation is a mature technology which decouples structure from its base and lengthens its natural period of vibration. However, existing base isolation devices must possess certain lateral resistance to withstand service lateral forces such as wind, and such stiffness hinders the effectiveness of vibration isolation. In addition, supplementary damping devices are sometimes added to control excessive displacements in isolation level. This paper proposes a smart system which changes the property of a base isolation system upon EEW signal. In normal times when earthquake risk is not present, the base isolation system is locked by shear keys. When an earthquake is signalled by the EEW system, a mechanical system releases the base isolation system. When the earthquake ceases, the system resets and base isolation is locked again. On-board vibration sensors are added to activate the system in case of EEW fails to detect incoming waves. A crucial benefit of the system is that supplementary damper is no longer required to control excessive isolator displacements, and elastic stiffness of base isolation is no longer required to re-enter the base isolation system. The result is that it maximizes the vibration isolation effectiveness. A conceptual framework of proposed system is described and demonstrated by laboratory-scaled experiments. A 6-storey test frame is excited on a shake table subjected to historical earthquakes. Results indicates that the proposed system is effective in reducing earthquake responses on the building. It is an IoT-enabled earthquake-risk mitigation system.

Experimental realisation of the real‐time controlled smart magnetorheological elastomer seismic isolation system with shake table

Traditional base isolation protects structures against severe seismic events by providing a designated lateral flexibility at the base level of the structures. Due to its inherent passive nature, in the design process, compromises have to be made among performance of different design targets (displacements, interstorey drifts, accelerations, etc.). In addition, as the working principle, the effectiveness of a base isolation relies on the degree of “decoupling” between ground excitation and superstructure. However, a higher degree of decoupling compromises the stability of the structures. In other words, for a base solation system, it possesses inherent conflicts between the effectiveness of the isolation and the lateral stability of the structure. A concept of new smart base isolation system is proposed, in which real-time controllable decoupling for a base isolation structure is achieved by employing magnetorheological elastomer (MRE) base isolators. With controllable lateral stiffness, the smart base isolation system can achieve an optimal decoupling by instantly shifting the structure's natural frequencies to a nonresonant region. This paper aims at experimentally proving and validating this innovative concept, including designing a three-storey shear building model equipped with MRE base isolators, demonstrating the feasibility and evaluating the performance of the proposed system by a series of shake table testing. The comprehensive experimental design and results of shake table testing have concept-proved the proposed smart MRE base isolation system for future development in practical applications.

Overview of the development of smart base isolation system featuring magnetorheological elastomer

Despite its success and wide application, base isolation system has been challenged for its passive nature, i.e., incapable of working with versatile external loadings. This is particularly exaggerated during near-source earthquakes and earthquakes with dominate low-frequency components. To address this issue, many efforts have been explored, including active base isolation system and hybrid base isolation system (with added controllable damping). Active base isolation system requires extra energy input which is not economical and the power supply may not be available during earthquakes. Although with tunable energy dissipation ability, hybrid base isolation systems are not able to alter its fundamental natural frequency to cope with varying external loadings. This paper reports an overview of new adventure with aim to develop adaptive base isolation system with controllable stiffness (thus adaptive natural frequency). With assistance of the feedback control system and the use of smart material technology, the proposed smart base isolation system is able to realize real-time decoupling of external loading and hence provides effective seismic protection against different types of earthquakes.

Vibration Control Of Steel Frames Using Magnetorheological Dampers: A New Control Algorithm.

Control technologies application to steel structure is mainly anticipated to enhance the structural performance against natural hazards. In particular smart base isolation system connected with semi-active isolator at the base with controllable semi devices gaining impulse for its efficiency and economic reasons. Generally the development of control design strategies through system dynamics concept had not been considered entirely for structural applications. Structural characteristics which help to divulge structural properties, hitherto flout by civil engineering circle are assimilated with control techniques to construct indices in modal and nodal coordinates for the endurance of the control action to utilize their fullest capabilities. In this study, an isolated 3D steel frame model is developed. Magneto-Rheological dampers are fixed with 3D steel frame model which act as a smart control device. Besides, Force transducers and Piezoresistive Actuator in tandem with Deltatron conditioning amplifier are also used. Presently many techniques are employed for the optimum placement of actuators and sensors in vibration control systems. The concept of controllability-observability is used in these methods. The specific relationship between the vibration modes and controllability-observability simplifies this approach. This study envisaged the compatibility of force transducers along with triaxial and uniaxial accelerometers fixed at various trial spots on the model structure to quantify the damping force and absolute accelerations of the structure and the dampers individually, positioned in the system, against the excitation of the structure.

Seismic response control of multi-story base-isolated buildings using a smart electromagnetic friction damper with smooth hysteretic behavior

Abstract This paper studies the use of a smart/semi-active electromagnetic friction damper (SEMFD) for the control of seismic response of multi-story base-isolated buildings. The SEMFD consists of a ferromagnetic plate and two similar arrays of thick rectangular ferromagnetic-core coils (FCs) connected in series. The FCs are attached to the two sides of the ferromagnetic plate through two non-magnetic friction pads. The force in the damper is developed because of the friction between the friction pads and the ferromagnetic plate when the FCs moves relative to ferromagnetic plate. The normal force between the friction pad and the ferromagnetic plate is caused by the attractive magnetic interactions between the FCs arrays and the ferromagnetic plate. The magnitude of this force is controlled by a proposed semi-active controller that is capable of varying the current flowing through the FCs in such a way that it is able to avoid stick-slip motion by smoothing the nonlinear hysteretic behavior of the SEMFD. The capability of the SEMFD and the proposed semi-active controller to control the seismic response of base-isolated buildings is demonstrated by implementing them into the dynamic model of a six-story base-isolated building supported on lead-rubber bearings (LRBs). The numerical results show that the SEMFD and its semi-active controller are capable of limiting the displacement of the base floor without noticeably increasing the inter-story drifts and absolute accelerations of the floors. It is demonstrated that the parallel actions of the LRBs and the SEMFD in the base floor create a smart base isolation system that is capable of fully protecting a multi-story building from ground motions with intensities at a level as that of the ASCE 7–10 Maximum Considered Earthquake (MCE).

A smart mechatronic base isolation system using earthquake early warning

In earthquake-prone countries such as Japan, effects of earthquakes are one of the major design objectives in buildings and infrastructures. Recent advances in earthquake engineering have improved the safety and reliability of buildings and infrastructures. Better understanding of geomorphology of earthquakes also enables us to better predict and estimate propagation of such natural hazard. For example, the Earthquake Early Warning (EEW) system in Japan provides advanced warnings using the different arrival times of P and S waves. On the other hand, techniques and methods in passive, semi-active and active vibration control have flourished. Base-isolation is a proven technique which enhances earthquake resilience of buildings and bridges. In general, this technique involves decoupling a superstructure from its foundation and lengthens its natural period of vibration. This technique is mature and commercialization has taken place worldwide. However, wind-resistance of base-isolated structures is generally a concern as the lateral stiffness of a base-isolated structure is low and serviceability wind effects may induce unacceptable lateral movement and/or vibration of the structure. This paper presents a new concept which the base-isolation system is activated by EEW system through a mechatronic system. In other times the structure is not base-isolated and provides strong lateral resistance against wind loads. As a backup design, the proposed system also equips with its own network of accelerometers which can trigger base isolation system independent from EEW system. The smart mechatronic base isolation system is fully automated, and resets itself after each ground motion. The paper describes the conceptual framework of proposed system and presents laboratory-scaled proof-of-concept experiments. Four historical earthquake time histories were used as ground excitations. Structural responses are compared between the two triggering mechanisms and results are discussed. Finally, the concept of Internet of Things (IoT) which make use of EEW is discussed, allowing connectivity between a single control unit and a network of infrastructures to achieve economy of scale.

Experimental study of semi-active magnetorheological elastomer base isolation system using optimal neuro fuzzy logic control

Abstract In this paper, a “smart” base isolation strategy is proposed in this study utilising a semi-active magnetorheological elastomer (MRE) isolator whose stiffness can be controlled in real-time and reversible fashion. By modulating the applied current, the horizontal stiffness of the MRE isolator can be controlled and thus the control action can be generated for the isolated structure. To overcome the inherent nonlinearity and hysteresis of the MRE isolator, radial basis function neural network based fuzzy logic control (RBF-NFLC) was developed due to its inherent robustness and capability in coping with uncertainties. The NFLC was optimised by a non-dominated sorting genetic algorithm type II (NSGA-II) for better suited fuzzy control rules as well as most appropriate parameters for the membership functions. To evaluate the effectiveness of the proposed smart base isolation system, four scenarios are tested under various historical earthquake excitations, i.e. bare building with no isolation, passive isolated structure, MRE isolated structure with Bang-Bang control, MRE isolated structure with proposed NFLC. A three-storey shear building model was adopted as the testing bed. Through the testing results, limited performance of passive isolation system was revealed. In contrast, the adaptability of the proposed isolation strategy was demonstrated and it is proven that the smart MRE base isolation system is able to provide satisfactory protection for both structural and non-structural elements of the system over a wide range of hazard dynamic loadings.

APPROPRIATE BASE STIFFNESS OF SMART BASE ISOLATION SYSTEM

In this paper, the effect of base stiffness on the performance of hybrid control system of base isolation system and magnetorheological (MR) damper has been studied and its appropriate base stiffness has been determined. Many researches have been proposed that in the structure controlled by the single base isolation system without MR damper, the base stiffness should be designed such that the fundamental period of isolated structure is almost triple the fundamental period of fixed-base structure. To determine the appropriate base stiffness of hybrid control system, different values have been considered as base stiffness and MR damper has been also employed in two cases of passive form that voltage and dynamical behaviour of MR damper is constant (hybrid base isolation) and semi-active form that MR damper voltage is applied by H2/linear quadratic Gaussian (LQG) and clipped-optimal control algorithms (smart base isolation). For numerical simulation, a three-story shear frame has been subjected to El Centro, Northridge and Tabas earthquakes. Results show that in the structure controlled by the single base isolation system, the peak responses of structure strongly depend on the base stiffness while the sensitivity of peak responses to the base stiffness is lower when the structure is controlled by hybrid base isolation system. According to results, it can be concluded that the peak base drift of hybrid base isolation system reduces with the increase of the base stiffness while this reduction trend is less considerable in the stiffness that are more than the proposed stiffness for the single base isolation system. Hence the proposed stiffness for single base isolation system is the appropriate stiffness for hybrid base isolation system, too. Results also show that under earthquakes considered in this paper, the smart base isolation system is mostly more effective than hybrid base isolation system in mitigating and controlling both root mean square and maximum of structure responses such as base drift, inter-story drift and acceleration.

APPROPRIATE BASE STIFFNESS OF SMART BASE ISOLATION SYSTEM

In this paper, the effect of base stiffness on the performance of hybrid control system of base isolation system and magnetorheological (MR) damper has been studied and its appropriate base stiffness has been determined. Many researches have been proposed that in the structure controlled by the single base isolation system without MR damper, the base stiffness should be designed such that the fundamental period of isolated structure is almost triple the fundamental period of fixed-base structure. To determine the appropriate base stiffness of hybrid control system, different values have been considered as base stiffness and MR damper has been also employed in two cases of passive form that voltage and dynamical behaviour of MR damper is constant (hybrid base isolation) and semi-active form that MR damper voltage is applied by H2/linear quadratic Gaussian (LQG) and clipped-optimal control algorithms (smart base isolation). For numerical simulation, a three-story shear frame has been subjected to El Centro, Northridge and Tabas earthquakes. Results show that in the structure controlled by the single base isolation system, the peak responses of structure strongly depend on the base stiffness while the sensitivity of peak responses to the base stiffness is lower when the structure is controlled by hybrid base isolation system. According to results, it can be concluded that the peak base drift of hybrid base isolation system reduces with the increase of the base stiffness while this reduction trend is less considerable in the stiffness that are more than the proposed stiffness for the single base isolation system. Hence the proposed stiffness for single base isolation system is the appropriate stiffness for hybrid base isolation system, too. Results also show that under earthquakes considered in this paper, the smart base isolation system is mostly more effective than hybrid base isolation system in mitigating and controlling both root mean square and maximum of structure responses such as base drift, inter-story drift and acceleration.

A dual-loop adaptive control for minimizing time response delay in real-time structural vibration control with magnetorheological (MR) devices

Time delay is a challenge issue faced by the real-time control application of the magnetorheological (MR) devices. Not to deal with it properly may jeopardize the effectiveness of the control, even lead to instability of the control system or catastrophic failure. This paper proposes a dual-loop adaptive control to address the response time delay associated with MR devices. In the proposed dual-loop control, the inner loop is designed to compensate the time delay of MR device induced by the PWM current driver. While the outer loop control can be any structural control algorithm with aims to reducing structural responses of a building during extreme loadings. Here an adaptive control strategy is adopted. To verify the proposed dual-loop control, a smart base isolation system employing magnetorheological elastomer base isolators is used as an example to illustrate the control effect. Numerical study is then conducted using a 5 -storey shear building model equipped with smart base isolation system. The result shows that with the implementation of the inner loop, the control current can instantly follow the control command which reduce the possibility of instability caused by the time delay. Comparative studies are conducted between three control strategies, i.e. dual-loop control, Lyapunov’s direct method based control and optimal passive base isolation control. The results of the study have demonstrated that the proposed dual-loop control strategy can achieve much better performance than the other two control strategies.

A genetic algorithm–based design approach for smart base isolation systems

This article presents a new approach for designing effective smart base isolation systems composed of a low-damping linear base isolation and a semi-active magneto-rheological damper. The method is based on transforming the design procedure of the hybrid base isolation system into a constrained optimization problem. The magneto-rheological damper command voltages have been determined using H2/linear quadratic Gaussian and clipped-optimal control algorithms. Through a sensitivity analysis to identify the effective design parameters, base isolation and control algorithm parameters have been taken as design variables and optimally determined using genetic algorithm. To restrict increases in floor accelerations, the objective function of the optimization problem has been defined as minimizing the maximum base drift while putting specific constraint on the acceleration response. For illustration, the proposed method has been applied to design a semi-active hybrid isolation system for a four-story shear building under earthquake excitation. The results of numerical simulations show the effectiveness, simplicity, and capability of the proposed method. Furthermore, it has been shown that using the proposed method, the acceleration of the isolated structure can also be incorporated into design process and practically controlled with a slight sacrifice of control effectiveness in reducing the base drift.