Base-isolated Benchmark Building Research Articles

Mitigation of Earthquake Responses Using SMA Supplemented Base-Isolation Devices for Benchmark Building

The efficiency of traditional isolation bearings is doubted for near-field earthquakes because these bearings undergo large displacement. A comparative study of different base isolation systems of base-isolated benchmark building is carried out in the present study. The study is based on assumption that buildings are bi-directionally acted upon by near-field earthquakes for assessing their relative performance in seismic control of the benchmark building. The time history variations of important response parameters and evaluation criteria of the benchmark building has been studied for assessing the effectiveness of the isolation systems. The Shape Memory Alloy (SMA) is utilized with elastomeric bearings and friction bearings to study the effectiveness of SMA wires with different isolators. The benchmark building is modelled as a discrete linear elastic shear structure having three degrees of- freedom at each floor level. Time domain dynamic analysis of this building has been carried out with the help of constant average acceleration Newmark’s method and equilibrium of non-linear forces has been taken care by fourth order Runge-Kutta method. The comparative performance of various isolation systems has been studied with uniform and hybrid combinations. The hybrid combination of SMA supplemented bearings works out the better isolation system keeping in view of the percentage reduction in evaluation criteria for smart base-isolated benchmark building. Furthermore, it is shown that, the functionality of SMA wire is not efficient with Lead Rubber Bearing system, as it is able to control displacement but increases the acceleration, base shear, story drift and isolation forces.

Semiactive conceptual fuzzy control of magnetorheological dampers in an irregular base-isolated benchmark building optimized by multi-objective genetic algorithm

Seismic base isolations are well-established passive control systems, used for reducing structural responses and preventing interior sensitive equipment and nonstructural elements from damaging. However, in a base-isolated structure under near-fault earthquakes, isolated layers sustain large displacements that might not be allowable. Further, any passive limitation in these displacements amplifies vibration transmissions to the superstructure. Smart hybrid base isolations using magnetorheological (MR) dampers, as well-known semiactive devices, can overcome this problem by smart dampening. Nonetheless, highly nonlinear hysteretic behavior of MR dampers is one of the challenges for model-based control algorithms. In this study, a smart multi-objective fuzzy-genetic control for dampening the vibrations of structures in an irregular base-isolated benchmark building subjected to different earthquake scenarios is presented. The control aims, on one hand, to conserve (or even improve) top isolation characteristics in unique restraining of floor accelerations and drifts and, on the other hand, to mitigate large base displacements under near-fault earthquakes using MR dampers simultaneously. Unlike many smart controls with a black-box performance, the proposed fuzzy core is constructed conceptually employing control expertise with respect to the plant. To achieve control objectives, a conceptual innovative feedback is proposed for fuzzy decision making. To optimize this human-designed controller, a multi-objective genetic algorithm is applied. For evaluation, a three-dimensional nonlinear irregular base-isolated benchmark building planned by the American Society of Civil Engineers is employed. In comparison with classical and smart controls, the results demonstrate that despite having the smallest structure with fast performance, the proposed control effectively diminishes conflicting responses and has better performance than other controls.

Adaptive control of earthquake-excited nonlinear structures with real-time tracking on prescribed performance criteria

A model reference adaptive control method is proposed to suppress the nonlinear responses of earthquake-excited structures with the proposed implementation of performance tracking criteria. The model reference concept is adopted to propose a comprehensive framework for real-time tracking on prescribed performances, and a deterministic reference model is presented to explicitly represent the prior-designed structural performances. The tracking error and the time-varying adaptive control law are systematically presented and designed by using the backstepping theory and the Lyapunov stability analysis. Little prior or explicit knowledge of structural nonlinear behavior is considered for the proposed adaptive backstepping law. Two performance schemes, inspired by the classical linear quadratic regulator control theory and the unknown disturbance cancelation, are developed. Illustrative examples of a bilinear single-degree-of-freedom system and a seismically base-isolated benchmark building structure are employed with a detail illustration and discussion about the control performance of the proposed methodology. Finally, an additional parametric study on the issues of the actuator saturation, the optimum parameter selection, and the switching delay is presented and discussed.

Negative stiffness device for seismic protection of smart base isolated benchmark building

This paper presents a novel negative stiffness device (NSD) for the seismic protection of the base isolated benchmark building in near fault earthquake. The benchmark structure has eight stories and irregular plan, and the superstructure is considered to be a linear elastic system with lateral torsional behavior. Furthermore, it is equipped with low damping elastomeric rubber bearings and viscous dampers for seismic protection. The proposed NSD can change the stiffness of composite structure-device assembly, emulate “apparent yielding” of the structure system without permanent deformations. It consists of a highly compressed spring, a wheel and a curved template that the wheel can roll on. The device can achieve any force-displacement behavior within its designed range. Experimental results are presented to verify the analytical model of the NSD. Numerical simulation results under seven earthquake inputs show that the proposed device is effective in reducing the response of the base and superstructure in comparison with a sample clipped optimal controller and an H2/LQG sample controller.

Response spectrum analysis considering non-classical damping in the base-isolated benchmark building

An isolated building, composed of superstructure and isolation system which have very different damping properties, is typically non-classical damping system. This results in inapplicability of traditional response spectrum method for isolated buildings. A multidimensional response spectrum method based on complex mode superposition is herein introduced, which properly takes into account the non-classical damping feature in the structure and a new method is developed to estimate velocity spectra from the commonly used displacement or pseudo-acceleration spectra based on random vibration theory. The error of forced decoupling method, an approximated approach, is discussed in the viewpoint of energy transfer. From the baseisolated benchmark model, as a numerical example, application of the procedure is illustrated companying with comparison study of time-history method, forced decoupling method and the proposed method. The results show that the proposed method is valid, while forced decoupling approach can\'t reflect the characteristics of isolated buildings and may lead to insecurity of structures.

Equivalent linear elastic-viscous model of shape memory alloy for isolated structures

In this investigation, the equivalent linear elastic-viscous model of shape memory alloy (SMA) is established for seismic analysis of base-isolated structures using system identification method. The necessary key parameters to express the hysteresis loop of SMA are austenite stiffness, transformation strength, ductility ratio, and stiffness ratio. These parameters are considered in the modeling. This model is developed based on the American Association of State Highway and Transportation Officials (AASHTO) isolation guidelines. In order to validate the proposed model, the base-isolated benchmark building is analyzed by using proposed equivalent linear SMA model as well as the different non-linear SMA models. The evaluation criteria given in the benchmark problem and time variation of top-floor absolute accelerations and base-displacements are considered for comparing the linear and nonlinear models of SMA. An excellent agreement is achieved between proposed equivalent linear SMA model and its nonlinear models. The seismic code recommends that the equivalent linear model of the nonlinear system can be used for carry out the response spectrum analysis of base-isolated structures. Furthermore, the non-linear model requires computationally more time and effort, especially for larger degrees of freedom system. The proposed model may be useful to design engineers in order to over come the disadvantage of non-linear models.

Influence of high austenite stiffness of shape memory alloy on the response of base-isolated benchmark building

The influence of high austenite stiffness of shape memory alloy (SMA) on the response of base-isolated benchmark building has been investigated. Dynamic analysis was performed by solving the governing equations of motion using Newmark-beta method under three near-fault earthquake motions. The super-elastic behavior of SMA was modeled by the Grasser–Cozzarelli model. Structural response parameters such as top-floor acceleration, base displacement, and base shear were chosen for investigation. Three near-fault earthquakes with bidirectional ground motions were considered. It was observed that because of high austenite stiffness of SMA, higher accelerations associated with high frequencies are transmitted to the superstructure. The isolation device with high austenite stiffness of SMA excites the higher modes of the base-isolated structure and thus magnifies the floor accelerations. This phenomenon can be detrimental to the high-frequency internal equipments mounted in the base-isolated structure. On the other hand, the high austenite stiffness of SMA does not affect the base displacement and base shear of the base-isolated structure significantly. Furthermore, the influence of high austenite stiffness of SMA is dependent on the transformation strength of SMA and flexibility of the isolator. Copyright © 2016 John Wiley & Sons, Ltd.

The Computational Analysis and Evaluation on the Seismic Response of Base Isolated Benchmark Building

Based on the base isolated benchmark building, the dynamic calculation methods of the seismic response were established. Through the computational analysis and comparison of the non-isolation situation and two isolation situations, the influence of the isolation effect about base isolation system stiffness, damping and the method of stiffness arrangement were demonstrated on the platform of benchmark building. The isolated benchmark building was evaluated to offer some new basis about the model used in theoretical research and isolation designed as well as alternative ways to further broaden the base isolated benchmark building.

Performance-based semi-active control algorithm for protecting base isolated buildings from near-fault earthquakes

Base isolated structures have been found to be at risk in near-fault regions as a result of long period pulses that may exist in near-source ground motions. Various control strategies, including passive, active and semi-active control systems, have been investigated to overcome this problem. This study focuses on the development of a semi-active control algorithm based on several performance levels anticipated from an isolated building during different levels of ground shaking corresponding to various earthquake hazard levels. The proposed performance-based algorithm is based on a modified version of the well-known semi-active skyhook control algorithm. The proposed control algorithm changes the control gain depending on the level of shaking imposed on the structure. The proposed control system has been evaluated using a series of analyses performed on a base isolated benchmark building subjected to seven pairs of scaled ground motion records. Simulation results show that the newly proposed algorithm is effective in improving the structural and nonstructural performance of the building for selected earthquakes.

INFLUENCE OF HIGH INITIAL ISOLATOR STIFFNESS ON THE SEISMIC RESPONSE OF A BASE-ISOLATED BENCHMARK BUILDING

The influence of high initial isolator stiffness on the response of a base-isolated benchmark building is investigated. The base-isolated building is modeled as a three-dimensional linear-elastic structure having three degrees-of-freedom at each floor level. The time-history analysis of this building is carried out by solving the governing equations of motion using Newmark-beta method along with an iterative predictor–corrector approach. The force–deformation behavior of the isolation system is modeled by a bilinear law, which can be effectively used to model all isolation systems in practice. Three near-field earthquakes with bidirectional ground motions are considered. Structural response parameters such as absolute top floor acceleration, base shear, and base displacement are chosen for investigating the effects of high initial isolator stiffness. It was observed that the high initial isolator stiffness of the isolation system excites the higher modes in the base-isolated building and increases the top floor acceleration. Such a phenomenon can be detrimental to the sensitive instruments placed in the isolated structure. On the other hand, both the base displacement and base shear reduce marginally due to increase in the initial isolator stiffness. Further, the influences of high initial isolator stiffness are found to dependent on the period and characteristic strengths of the base isolation system.

Seismic Response of Base-Isolated Benchmark Building with Variable Sliding Isolators

The seismic response of base-isolated benchmark building with variable sliding isolators like variable friction pendulum system (VFPS), variable frequency pendulum isolator (VFPI), and variable curvature friction pendulum system (VCFPS), along with conventional friction pendulum system (FPS), was studied under the seven earthquakes. The earthquakes are applied bi-directionally in the horizontal plane ignoring vertical ground motion component. The shear type base-isolated benchmark building is modeled as three-dimensional linear elastic structure having three degrees of freedom at each floor level. Time domain dynamic analysis of the benchmark building was carried out with the help of constant average acceleration Newmark-Beta method and nonlinear isolation forces was taken care by fourth-order Runge-Kutta method. The base-isolated benchmark building is investigated for uniform isolation and hybrid isolation in combination with laminated rubber bearings through the performance criteria and time history response of important structural response parameters like floor accelerations, base displacement, etc. It is observed that variable sliding isolators performed better than conventional FPS due to their varying characteristic properties which enable them to alter the isolator forces depending upon their isolator displacements thus improves the performance of the structure. The VFPS efficiently controls large isolator displacements and VFPI and VCFPS improve super structural response on the cost of isolator displacement. It is also observed that the hybrid isolation is relatively better in comparison to the uniform isolation for the benchmark building.

Parameter identification of large-scale magnetorheological dampers in a benchmark building

Magnetorheological (MR) dampers are devices that can be used for vibration reduction in structures. However, to use these devices in an effective way, a precise modeling is required. In this sense, in this paper we consider a modified parameter identification method of large-scale magnetorheological dampers which are represented using the normalized Bouc-Wen model. The main benefit of the proposed identification algorithm is the accuracy of the parameter estimation. The validation of the parameter identification method has been carried out using a black box model of an MR damper in a smart base-isolated benchmark building. Magnetorheological dampers are used in this numerical platform both as isolation bearings as well as semi-active control devices.

Semiactive control strategy for a phase II smart base isolated benchmark building

This paper presents a semiactive control strategy for the seismic protection of the phase II smart base isolated benchmark building subjected to near-fault earthquakes. Magnetorheological (MR) fluid dampers controlled by an optimal direct output feedback control algorithm with a voltage generator are used as semiactive control devices. The benchmark building is an eight-story base isolated building, and the superstructure is considered to be a linear elastic system with lateral–torsional behavior. To reduce the energy transmitted to the structure from the ground, a combination of linear and nonlinear bearings is installed at the base of the structure. It is difficult to design the controller for this benchmark problem because of the nonlinear behavior of the isolation members. Linear control theory is frequently applied to nonlinear structures because there are no appropriate and well-defined control theories that can consider general types of nonlinearities. Therefore, to improve control performance, the nonlinearities of the isolation members are considered indirectly with the linear control theory during the design process of the controllers for the MR dampers. Numerical simulation results under various earthquake inputs show that the proposed control strategy is effective in reducing the responses of the isolation members as well as the superstructure. Therefore, the proposed control system could be used as an improved control strategy for base isolated buildings subjected to near-fault earthquakes. Copyright © 2008 John Wiley & Sons, Ltd.

Probabilistically robust nonlinear design of control systems for base-isolated structures

A stochastic-simulation-based nonlinear controller design for base-isolation systems is discussed in this study. The performance objective is the maximization of structural reliability, quantified as the probability, based on the available information, that the structural response trajectory will not exceed acceptable thresholds. A simulation-based approach is implemented for evaluation of the performance of the controlled system. This approach explicitly takes into account nonlinear characteristics of the structural response and the control law in the design process. A realistic probabilistic model for representation of near-fault ground motions is adopted in the design stage. The variability of future earthquake events is addressed by incorporating a probabilistic description for the ground-motion model parameters, leading to a design approach that is robust to probabilistic uncertainty. The methodology is illustrated through application to the base-isolated benchmark building with elastomeric and friction pendulum isolators and an array of regenerative force actuators. Skyhook control implementation is considered and an efficient scheme is presented for the clipping of the control forces in order to satisfy the actuator force constraints. The performance of the controlled system is evaluated under seven earthquake records using a number of metrics. Comparison with the performance of a similar network of viscous dampers is also discussed.

GA-optimized FLC-driven semi-active control for phase-II smart nonlinear base-isolated benchmark building

An optimized fuzzy logic control (FLC) algorithm is developed for the phase-II smart base-isolated benchmark building with nonlinear isolation system. A restart genetic algorithm-based optimization strategy has been used to change the fuzzy system properties like the fuzzy rule base, pre-scale gains, membership function type and parameters at every simulation step. Acceleration and relative velocity responses at the damper location have been taken as inputs to the FLC system. Voltage required by the magneto-rheological (MR) damper is obtained as an output from the FLC. The use of MR dampers in the benchmark study as a control device along with isolation bearings in the building renders the overall system nonlinear. The advantage of using a fuzzy rule base is its inherent ability to handle nonlinearities and uncertainties in structural behavior, input excitation, sensor, and actuator dynamics. As a consequence, FLC provides robustness to the control mechanism. Moreover, FLC-driven MR damper voltage monitoring provides a gradual and smooth change of voltage. In the present study, the number of sensors and actuators and their locations have been kept unchanged as in the sample controller provided in the benchmark study. Simulation results for FLC, the adaptive rule and fixed rule base type, and results from the sample controller provided have been tabulated and compared. Results obtained indicate improvement using the proposed control approach without considering a multi-objective nondominated solution, where the weight of objective functions can be varied. A stability test for the proposed adaptive rule base FLC has been shown.

Application of angular-mass dampers to base-isolated benchmark building

The angular-mass damper referred herein is a wheel that has concentrated mass on its perimeter. The rotational inertia of the wheel is employed to dampen the relative acceleration between two joints. The application of this kind of damper to civil engineering structures would be practical since the damper works passively. Since the angular mass is much more significant than the translational mass, the rotational mass damper does not significantly increase the translational earthquake-induced force. To study the effectiveness of the device in the seismically excited structures, the device is applied to the base-isolated benchmark building. The results show that the device can further reduce the responses of the already dampened benchmark building. Copyright © 2008 John Wiley & Sons, Ltd.

Semi-active control of seismically excited base-isolated building model with friction pendulum systems

In this paper, effectiveness of various semi-active friction control strategies in protecting the base-isolated benchmark building model with friction pendulum systems as isolators and subject to various prescribed near-field ground motions has been investigated. These friction control strategies include semi-active discontinuous pulse filter (SADPF) controller, semi-active continuous pulse filter (SACPF) controller and visco-elastic friction (VEF) controller. In addition, the linear passive viscous (LPV) damper is also considered for comparison. Both the SACPF and SADPF controllers are designed by using the augmented structure-pulse filter model recently proposed by the authors. Simulation results indicate that all these controllers are effective in mitigating the base displacements, although the reduction in base displacement may be accompanied by an increase in superstructure response quantities. The SACPF controller is found to be the most effective among semi-active controllers, including Sample Lyapunov controller, in the sense that (i) increase in superstructure response quantities is quite minimal or these response quantities are decreased as the base displacement is reduced, (ii) there is no amplification in peak base acceleration and (iii) the control force does not have chattering-type characteristics and control force is applied only when peak base displacement is significant. Copyright © 2008 John Wiley & Sons, Ltd.

Smart system design for a 3D base-isolated benchmark building

The application of control technologies to structures is expected to enhance a structure's performance in response to natural hazards. This study focuses on the development of control design strategies suitable for smart base isolation systems. The phase I benchmark problem for 3D base-isolated buildings is used as a case study to facilitate a direct comparison with the results of other designs. The smart base isolation system consisting of passive isolators and controllable semiactive devices at the base is employed for the demonstration and validation of these strategies. Magnetorheological (MR) dampers are used as the control devices and are placed in parallel with the isolation system. An H2/LQG control algorithm is used to determine the nominal control action and is used in conjunction with a clipped optimal decision block. Effective design for this complex system requires the use of control device and sensor placement techniques achieved with the consideration of the structure's physical properties. The use of correlation is also proposed to minimize redundancies in the placement of the sensors and devices. Simulation results demonstrate that the control technique is effective in improving the structural performance for a variety of earthquakes. Copyright © 2007 John Wiley & Sons, Ltd.

GA-fuzzy control of smart base isolated benchmark building using supervisory control technique

The effectiveness of a supervisory fuzzy control technique for reduction of seismic response of a smart base isolation system is investigated in this study. To this end, a first generation, base isolated, benchmark building is employed for numerical simulation. The benchmark structure under consideration has eight stories and an irregular plan. Furthermore it is equipped with low damping elastomeric bearings and magnetorheological (MR) dampers for seismic protection. The proposed control technique employs a hierarchical structure of fuzzy logic controllers (FLC) consisting of two lower-level controllers (sub-FLC) and a higher-level supervisory controller. One sub-FLC has been optimized for near-fault earthquakes and the other sub-FLC is well-suited for far-fault earthquakes. These sub-FLCs are optimized by use of a multi-objective genetic algorithm. Four objectives, i.e. reduction of peak superstructure acceleration, peak isolation system deformation, RMS superstructure acceleration and RMS isolation system deformation are used in a multi-objective optimization process. When an earthquake is applied to the benchmark building, each of the sub-FLCs provides different command voltages for the semi-active controllers and the supervisory fuzzy controller appropriately combines the two command voltages based on a fuzzy inference system in real time. Results from numerical simulations demonstrate that isolation system deformation as well as superstructure responses can be effectively reduced using the proposed supervisory fuzzy control technique in comparison with a sample clipped optimal controller.

Cubic control for phase I smart base-isolated benchmark building with emphasis on nonstructural performance

Most control techniques in the structural engineering literature are aimed at improving performance of the primary structural system, but may have limited or even adverse effect on nonstructural components during strong seismic events. In this paper, we emphasize nonstructural performance using an active controller with a cubic nonlinearity. The controller is optimized based on the frequency response functions of a SDOF nonlinear oscillator. An eight-storey base-isolated benchmark building recently proposed by the ASCE structural control committee is studied as a demonstration by considering both structural and nonstructural performance indices. We compare the performance of the proposed cubic controller with that of a LQG-based semiactive control system and a passive energy dissipation system. It is shown from the simulation results that in most benchmark test cases, the cubic control system produces better nonstructural performance while maintaining good response characteristics of the primary structural system. Further research directions for this cubic control system are also pointed out. Copyright © 2005 John Wiley & Sons, Ltd.