Semi‐active friction system with amplifying braces for control of MDOF structures

The development and applications of a semi‐active friction damping system with amplifying braces is studied. A system of dampers and braces, defined as the friction damping system with amplifying braces (FDSAB) is considered. Active control theory with velocity and acceleration feedback is used to obtain the control forces in the proposed system. The system can be used efficiently to enhance the damping of a structure and improving its response. The efficiency of the proposed system is demonstrated by the numerical simulation of a seven storey building subjected to earthquakes. The simulation shows that the behaviour of the damped structure with the FDSAB is significantly improved. The required control forces are much less compared with a control system with semi‐active friction dampers connected either to chevron or diagonal braces. Copyright © 2001 John Wiley & Sons, Ltd.     

Seismic response of semi‐active friction‐damped reinforced concrete structures with self‐variable stiffness

The influence of structural self‐variable stiffness and semi‐active friction dampers on the behavior of reinforced concrete (RC) buildings during strong earthquakes is discussed. A fully braced six‐story beamless RC frame is analyzed. The effect of concrete braces (with only constructive reinforcement) as a self‐variable mechanism is studied. It is shown that up to a certain limit the frame itself controls its behavior by adapting its dynamic characteristics in the real time of the earthquake. This self‐adaptation is achieved by autonomous disengagement of the braces under tension and their further nonlinear action under compression. The system has several levels of seismic adaptation, and it selects one of them for enhanced response to the given earthquake. However, when the limit is reached, further self‐adaptation of the frame becomes impossible. The occurrence of an earthquake of higher magnitude can then lead to disengagement of the concrete braces under compression, intensifying structural damage and even causing collapse. The use of semi‐active controlled friction dampers is proposed as a means of preventing the collapse of braces under compression, thereby enabling structures to withstand earthquakes. The forces in the friction dampers are regulated according to an optimal control algorithm. Modulation of the friction level in real time during the earthquake yields additional improvement of structural seismic behavior and obviates the need for retrofitting. Copyright © 2007 John Wiley & Sons, Ltd.     

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

This 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.     

Semi‐active control of seismic response of tall buildings with podium structure using ER/MR dampers

A tall building with a large podium structure under earthquake excitation may suffer from a whipping effect due to the sudden change of building lateral stiffness at the top of the podium structure. This paper thus explores the possibility of using electrorheological (ER) dampers or magnetorheological (MR) dampers to connect the podium structure to the tower structure to prevent this whipping effect and to reduce the seismic response of both structures. A set of governing equations of motion for the tower–damper–podium system is first derived, in which the stiffness of the member connecting the ER/MR damper to the structures is taken into consideration. Based on the principle of instantaneous sub‐optimal active control, a semi‐active sub‐optimal displacement control algorithm is then proposed. To demonstrate the effectiveness of semi‐active control of the system under consideration, a 20‐storey tower structure with a 5‐storey podium structure subjected to earthquake excitation is finally selected as a numerical example. The results from the numerical example imply that, as a kind of intelligent control device, ER/MR dampers can significantly mitigate the seismic whipping effect on the tower structure and reduce the seismic responses of both the tower structure and the podium structure. Copyright © 2001 John Wiley & Sons, Ltd.     

Selective combined control stiffness and magnetorheological damping system in nonlinear multistorey structures

The application of a combined controlled stiffness and magnetorheological (MR) damping system in a base‐isolated nonlinear multistorey structure with amplifying braces is described. Passive control theory is used to obtain the viscous characteristics of the MR damper fluid. Selective control of the proposed system is used to enhance the behaviour of a structure during earthquakes. The nonlinear equations of motion are solved using the Wilson θ method. The control forces are obtained using instantaneous control theory with the predictive control approach. The efficiency of the proposed system is demonstrated by a numerical simulation of a seven‐storey building subjected to four different earthquakes. The stimulation shows that the behaviour of the selective controlled structure with the proposed damping system is significantly improved compared to that of an uncontrolled structure. The energy required for the adjustment of the proposed system with amplifying braces is much lower compared to that of the case of MR dampers connected directly to chevron braces. The response of the predictive controlled structure is close to that of an instantaneous controlled structure. Copyright © 2002 John Wiley & Sons, Ltd.     

Active and Semi‐active Adaptive Control for Undamaged and Damaged Building Structures Under Seismic Load

Abstract: During the lifetime of a structural system, many severe events such as earthquakes and strong winds may impact the system and result in potential damage. To mitigate the structural vibration and damage during these extreme events, control devices such as active and semi‐active devices have received considerable attention because of their attractive characteristics. Active control devices are adaptable to any change and semi‐active devices have the capability of offering the reliability of passive devices and the versatility and adaptability of active devices. In this research, a direct‐adaptive‐control method is used to control the behavior of an undamaged and a damaged structure using semi‐active and active devices. In the adaptive control method, the controlled system is forced to behave like the model system which exhibits the desired behavior. The model of the adaptive control method is defined in a way to optimize the response of the controlled structure. The controller developed using this method can deal with changes that occur in the characteristics of the structure because it can modify its parameters during the control process. A magnetorheological (MR) damper is used as the semi‐active device in this study, whereas a hydraulic actuator is utilized as the active device to control the behavior of the structure. The performance of a three‐story building from the SAC project for the third generation of the control benchmark problem is studied by performing time–history analyses. The structure is subjected to different earthquakes and controlled by the direct adaptive control method. In the analysis of the structure, some stiffness reduction is assumed as a result of potential damage in the first story of the building. Also, the direct adaptive control strategy is used to optimize the response of the undamaged structure and to mitigate the damage impact on the performance of the controlled structure in the presence of noise for output measurements. The results of adaptive control method are compared with those of other control strategies. It is shown that the performance of the three‐story building is improved using the adaptive control method. By assessing the results of different control approaches, it is found that the adaptive control method works more effectively than other methods and semi‐active devices can provide reliable results.     

On the efficiency of semi‐active smart structures: self‐regulating MR dampers control system for tall buildings

Many severe dynamical loadings such as earthquakes and strong winds may subject to structural systems during their lifetime and lead to changes in structural characteristics. Hence, employing an adaptive control strategy that can deal with these alterations compound with design of the structural elements would undoubtedly be the most effective alternative design for the old‐fashioned design methods, which are relatively inefficient in response to these unforeseen conditions. In the current study, benefits of employing the modern control systems for design of tall buildings in comparison with the uncontrolled traditionally designed structures are thoroughly investigated. To contract the vibrational responses due to seismic excitations, the innovative direct‐modulating semi‐active controller is designed for magneto‐rheological dampers, which are installed in an 11‐storey sample building converting it to a smart structure. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance of fixed‐parameter control algorithms on high‐rise structures equipped with semi‐active tuned mass dampers

The present study investigates the performance of fixed parameter control algorithms on wind‐excited high‐rise structures equipped with semi‐active tuned mass dampers of variable damping. It has been demonstrated that the algorithms that increase significantly the performance of the controlled structure do so at the expense of damper strokes. When the maximum damper strokes are capped to progressively lower limits, the efficacy of different algorithms, measured through a number of performance objectives, drastically alters totally changing the performance ranking of them and pointing out the need for an extensive study of the interplay between loading, control algorithm and allowable stroke within the design of semi‐active tuned mass dampers devices. 2015 The Authors. The Structural Design of Tall and Special Buildings published by John Wiley & Sons Ltd.     

Semi‐active control devices in structural control implementation

A semi‐active control device for structural control implementations is presented and discussed in this paper. Based on two passive control devices, the mass pump and the hydraulic mass system, a new passive control system, the mass damper pump (MDP), is introduced. It is found that the MDP system is more effective in vibration control than the other two passive control systems. It is then shown that the passive control MDP can be modified to be a semi‐active control device and is very effective in structural control. Through theoretical analysis and numerical simulations, it is found that the proposed semi‐active control device MDP is more suitable for structures with ordinary height or the magnitude of earthquake excitations is not very large (because the control force provided by the semi‐active control is limited). Under these situations, the maximum response of a controlled structure can be reduced by one‐third to one‐half. Also, it is found that multiple MDP is more effective in reducing structural response than a single MDP when they are placed in appropriate locations. Copyright © 2005 John Wiley & Sons, Ltd.     

Support vector machine based semi‐active control of structures: a new control strategy

The present paper presents the support vector machine (SVM)‐based semi‐active control algorithm used for designing general dampers for multistorey structures under earthquakes. First, the linear quadratic regulator (LQR) controller for the numerical model of a multistorey structure formulated using the dynamic dense method is obtained by using the classic LQR control theory. Then, a SVM model is designed and trained to emulate the performance of the LQR controller. Likewise, this SVM model comprises the observers and controllers of the control system. Finally, in accordance with the features of general semi‐active dampers, a SVM‐based semi‐active control strategy is put forward. More specifically, an online auto‐feedback semi‐active control strategy is developed and then realized by resorting to SVM. In order to numerically verify the control effectiveness of the present control strategy, the time history analysis has been implemented to a structure with general dampers designed by the SVM‐based semi‐active control algorithm. In numerical simulations, four seismic waves including the El Centro, Hachinohe and Kobe waves, as well as the Shanghai artificial wave, whose peak ground accelerations are all scaled to 0.1 g, are taken into consideration. Comparative results demonstrate that general semi‐active dampers designed using the SVM‐based semi‐active control algorithm is capable of providing higher level of response reduction. Copyright © 2009 John Wiley & Sons, Ltd.     

A lattice‐shaped friction device and its performance in weak‐story prevention

Displacement‐dependent dampers with relatively low post‐yielding stiffness exhibits abrupt stiffness loss and can even induce notable damage concentrations under strong vibrations. A lattice‐shaped friction unit (LSFU) composed of steel strips and friction discs is proposed and it can dissipate most input energy through translational friction and rotational friction and provide post‐yielding stiffness through the axial strength of vertical strips. Measurements of the friction coefficient and torque coefficient ratio and quasi‐static analysis of the LSFU are conducted, the results indicate that the ratio rises first and then drops to a constant value. Under cyclic loading, the two friction mechanisms could work together effectively and the contribution of each component contained in the restoring force could be controlled by adjusting design parameters of the LSFU; the assembly accuracy of the components affect the resistance of vertical strips. The experiment results of two specimens are compared with those obtained from the developed formulas and numerical simulations. A design procedure and applicable style are proposed. Nonlinear seismic response analysis results show that these devices can reduce the displacement response effectively under small and moderate earthquakes and can also prevent concentrated damage and weak‐story occurrence in the structure relative to friction‐damped brace frame in strong earthquakes.     

Seismic response control of base‐isolated buildings using multiple tuned mass dampers

Seismic response of a base‐isolated building equipped with single tuned mass damper (STMD), multiple tuned mass dampers (MTMDs), and distributed multiple tuned mass dampers (d‐MTMDs) under real earthquake ground motions is investigated. Numerical study is carried out using analytical models of five‐, 10‐, and 15‐storey base‐isolated buildings equipped with the STMD, MTMDs, and d‐MTMDs. The buildings are modeled as shear‐type structure with a lateral degree of freedom at each floor level, and the buildings are isolated using the laminated rubber bearing, lead‐core rubber bearing, friction pendulum system, and resilient‐friction base isolator. The coupled differential equation of motion for the buildings are derived and solved in the incremental form using Newmark's step‐by‐step method of integration. From the numerical study conducted, it is concluded that installing a tuned mass damper at each floor level of a base‐isolated building reduces the structural response in terms of top floor acceleration and bearing displacement. It is found that installing the MTMDs and d‐MTMDs are significantly beneficial in reducing top floor acceleration as compared with the STMD. Further, almost comparable reduction in the bearing displacement could be obtained by installing the STMD, MTMDs at top, and d‐MTMDs in the base‐isolated buildings. The d‐MTMDs are more beneficial as compared with the STMD and MTMDs as otherwise huge controller mass can now be divided and distributed on different floor levels.     

Developing a Smart Structure Using Integrated Subspace‐Based Damage Detection and Semi‐Active Control

Damage detection in large building structures has always faced challenges due to analyzing the large amount of measured data. In this article, a new damage detection approach based on subspace method is proposed to identify damages using limited output data. Also, a new scheme is presented to develop a smart structure by integrating structural health monitoring with semi‐active control strategy. If damage occurs in such a structure under severe excitations, the proposed scheme has the capability to exert necessary control forces in order to compensate for damage and reduce simultaneously the dynamic response of the structure. The reliability and feasibility of the proposed method are demonstrated by implementing the technique to two shear building structures with semi‐active control devices. Results show that the damage could be identified accurately with saving time and cost due to less computation even under noise existence; and dynamic response is significantly reduced in the smart structure.     

Energy‐based damage assessment on structures during earthquakes

Several seismic damage indices have been developed using the energy concept in attempt to compensate for the inadequacy of ductility criteria. However, these indices are either based on implicitly defined energy as a cumulative effect on ductility or are unable to consider energy in a quantitative manner. In this paper, a method of assessing the structural performance during earthquakes based on both explicitly computed plastic rotation and plastic energy at every hinge of a moment‐resisting frame is proposed. This method uses the force analogy method to evaluate the structural response and energy in the inelastic domain. Inelastic deformation is expected to occur during major earthquakes, and active control based on an instantaneous optimal control algorithm is used to improve the structural performance. Comparisons are made between uncontrolled response and instantaneous optimal control response based on a single‐degree‐of‐freedom system to demonstrate the computation of plastic energy. Damage analysis of a six‐storey moment‐resisting steel frame is then presented to evaluate the performance and applicability of the proposed damage measure. Results show that the proposed damage assessment criteria are feasible and that active control can reduce plastic rotation and plastic energy, thereby reducing damage to a certain acceptable limit. Copyright © 2001 John Wiley & Sons, Ltd.     

Model‐Based Multi‐input,Multi‐output Supervisory Semi‐active Nonlinear Fuzzy Controller

Abstract: The authors recently proposed a new multi‐input, single‐output (MISO) semi‐active fuzzy controller for vibration control of seismically excited small‐scale buildings. In this article, the previously proposed MISO control system is advanced to a multi‐input, multi‐output (MIMO) control system through integration of a set of model‐based fuzzy controllers that are formulated in terms of linear matrix inequalities (LMIs) such that the global asymptotical stability is guaranteed and the performance on transient responses is also satisfied. The set of model‐based fuzzy controllers is divided into two groups: lower level controllers and a higher level coordinator. The lower level fuzzy controllers are designed using acceleration and drift responses; while velocity information is used for the higher level controller. To demonstrate the effectiveness of the proposed approach, an eight‐story building structure employing magnetorheological (MR) dampers is studied. It is demonstrated from comparison of the uncontrolled and semi‐active controlled responses that the proposed design framework is effective in vibration reduction of a building structure equipped with MR dampers.     

Semi‐active algorithm for energy‐based predictive structural control using tuned mass dampers

A novel semi‐active control algorithm is developed and numerically evaluated for the suppression of undesirable structural vibrations. The mechanical energy of the vibrating structure is considered as the primary variable influencing the control action. This intuitive strategy is proposed to realize improved control of structural vibrations. The numerical study conducted reveals that the proposed energy‐based predictive (EBP) algorithm can be implemented on vibration control applications. The energy imparted to the structure is also reduced due to the proposed algorithm. The influence of the parameters of the proposed semi‐active tuned mass damper is studied. Further, the application of the proposed strategy on a realistic structure is numerically demonstrated by implementing the algorithm for the wind response control of a 76‐story benchmark building. The results show that the EBP algorithm is a competitive semi‐active strategy. The robustness of the strategy is also evaluated considering uncertainties in the properties of the benchmark building.     

Seismic performance of MR frames protected by viscous or hysteretic dampers

This study concerns the behaviour of steel frames protected by different anti‐seismic devices (dampers). Typical hysteretic and viscous dampers are arranged in three steel moment‐resisting frames (MRFs) having different dynamical features but are designed to accomplish determined performance objectives. The proposed devices are selected following an iterative procedure based on the use of a suitable damage functional, which has been applied to control the behaviour of the protected structures under a specific seismic record. The outcomes obtained by implementing incremental dynamic analyses, carried out on the basis of seven historical records characterized by different features, allow to analyse the improvement of the structural performance due to the considered dampers and, therefore, to provide design information about their employment. The comparison of results is carried out taking into account the dampers capacity to protect the structures from damage, the inter‐storey drifts, the residual deformations and the possible amplification effects. In conclusion, the equivalent behaviour factors for each damper type are given, with the aim of providing useful design parameters for the implementation of simplified conventional linear analyses. Copyright © 2014 John Wiley & Sons, Ltd.     

结构半主动变刚度控制的研究

尽管已有的研究证明传统的变刚度控制系统可以有效地抑制结构在地震激励下动力响应,但是现有的变刚度装置仅能在很小的范围内改变结构的周期,而且也不利于抑制结构的加速度反应。为了克服这一局限性,本文提出了一种新型的半主动变刚度(ISAVS)控制系统,兼具基础隔震和传统变刚度控制的优点。基于作者提出的离复位控制策略,本文针对ISAVS系统进行了地震作用下的数值模拟,验证了它的可行性和有效性。     

Continuous pulse and hybrid control of structures

In recent years, passive as well as active control methods have been implemented for structural motion reduction of tall buildings in earthquakes. An active control method for the inelastic response of tall buildings is presented. The proposed method of continuous pulse control uses closed-loop feedback control as a combination of two algorithms. The first is a linear control algorithm-instantaneous optimal control-and the second is a pulse control algorithm-the pulse control algorithm-which applies a corrective pulse when a prespecified structural velocity threshold is exceeded. The control forces required by active control systems to reduce the seismic response of tall buildings can be quite large. On the other hand, passive control systems such as the viscoelastic dampers do not require external energy for their operation. The possibility of combining viscoelastic dampers and the active bracing system for reducing the required control forces is examined. The combination of passive and active devices improves safety, serviceability and the comfort of the building's occupants.