Semi-Active Adaptive Control of Coupled Structures for Seismic Hazard Mitigation

The research presented in this dissertation examines innovative structures connected with smart control devices driven by adaptive control methods. The research focuses on understanding the dynamics of coupled structures and evaluating the merits of adaptive control in enhancing the seismic performance of these structures and dealing with uncertainties. Coupled structures is recognized as an effective strategy to protect civil structures from seismic excitations. Coupling of adjacent structures has proved to offer functional benefits such as the potential for shifting the buildings’ natural frequencies, likely leading to a reduction in the natural period of vibration. Structural performance is further enhanced by implementing energy-dissipative devices to connect adjacent buildings to minimize the seismic structural responses. One of the main challenges to control civil structures is the high uncertainty involved throughout their lifetimes. Adaptive control promises to deal with changes in structures’ characteristics, such as seismic-induced damage. The simple adaptive control method, which is a reference-model following scheme, is used in the current research to improve the seismic behavior of adjacent buildings connected by structural links where control devices are implemented. The philosophy of the simple adaptive control method is that an actual system (often called plant) can be forced to track the behavior of pre-determined trajectories through adjustable adaptive gains. The effectiveness of the simple adaptive controller in reducing the seismic responses is compared with other adaptive and non-adaptive control methods. The results reveal that the simple adaptive controller is effective in alleviating the structural responses and dealing with uncertainties of coupled structures with both linear and nonlinear behavior. The results also show that the coupling strategy is viable for reducing the structural responses under seismic excitations

Optimization of force-limiting seismic devices connecting structural subsystems

This paper is focused on the optimum design of an original force-limiting floor anchorage system for the seismic protection of reinforced concrete (RC) dual wall-frame buildings. This protection strategy is based on the interposition of elasto-plastic links between two structural subsystems, namely the lateral force resisting system (LFRS) and the gravity load resisting system (GLRS). The most efficient configuration accounting for the optimal position and mechanical characteristics of the nonlinear devices is obtained numerically by means of a modified constrained differential evolution algorithm. A 12-storey prototype RC dual wall-frame building is considered to demonstrate the effectiveness of the seismic protection strategy

A Review on the Magnetorheological Fluid, Damper and Its Applications for Seismic Mitigation

Magnetorheological (MR) fluids and dampers have wide advances as smart materials because of its unique properties, notably, viscosity increases in the presence when magnetic field applied MR Fluids composed of three key components, including carrier fluid, surfactants and metal particles. The major applications of MR Fluids are in brakes, dampers, journal bearings, fluid clutches, pneumatic artificial muscles, aerospace etc. where electrical energy is converted to mechanical energy (Damping Force) in a controlled manner. Within a few milliseconds the fluid converts from liquid to semi solid state. Over the years, researchers were concerned on the ways to enhance the modelling precision. Though the proposed Dynamic models of MR Dampers represent displacement and force behaviour. In this review paper, the advances of MR Fluids, MR Damper, Damper Models, Energy harvesting and their applications for seismic resistance of structures are briefly discussed in the present study

A semi-active control system in coupled buildings with base-isolation and magnetorheological dampers using an adaptive neuro-fuzzy inference system

Connecting two buildings has been proved as an effective method of structural control for alleviating seismic responses. Researchers have proposed that two adjacent buildings through supplemental energy dissipating devices to mitigate the buildings’ responses. Numerous researchers have proposed various methods: active, passive, and semi-active control strategies. In Japan, some applications of coupled buildings control have been successfully implemented by utilizing passive and active control technology. Magnetorheological (MR) dampers have been identified as semi-active devices that can be used to reduce the vibration of the seismic structures during various types of ground motions. They can offer the adaptability of active devices, stability, and reliability of passive devices. Nevertheless, one of the difficulties in application of the MR dampers is the development of the appropriate control algorithms. Accordingly, this study presents the implementation of the adaptive neuro-fuzzy inference system (ANFIS) controller for earthquake hazard mitigation under coupled buildings control system with base-isolated building connecting to the free wall by MR dampers. The ANFIS whose training data is based on the Linear Quadratic Regulator (LQR) method is conducted to modify the parameters of the fuzzy logic controller and optimize the fuzzy rules. The performance of MR dampers is evaluated under seismic response. It is compared under four methods, including passive-off, passive-on, and two semi-active control strategies: ANFIS and LQR. Besides, various types of feedback of the ANFIS operated as two-input single output feedback system are investigated to assess the performance of the developed control scheme for structural vibration control. The numerical simulation results show that the proposed semi-active control system consisting of coupled buildings system and MR dampers by utilizing ANFIS can be effective in mitigating seismic responses of structures

A novel phenomenological model for dynamic behavior of magnetorheological elastomers in tension-compression mode

Tension-compression operation in MR elastomers (MREs) offers both the most compact design and superior stiffness in many vertical load-bearing applications, such as MRE bearing isolators in bridges and buildings, suspension systems and engine mounts in cars, and vibration control equipment. It suffers, however, from lack of good computational models to predict device performance, and as a result shear-mode MREs are widely used in the industry, despite their low stiffness and load-bearing capacity. We start with a comprehensive review of modeling of MREs and their dynamic characteristics, showing previous studies have mostly focused on dynamic behavior of MREs in shear mode, though the MRE strength and MR effect are greatly decreased at high strain amplitudes, due to increasing distance between the magnetic particles. Moreover, the characteristic parameters of the current models assume either frequency, or strain, or magnetic field are constant; hence, new model parameters must be recalculated for new loading conditions. This is an experimentally time consuming and computationally expensive task, and no models capture the full dynamic behavior of the MREs at all loading conditions. In this study, we present an experimental setup to test MREs in a coupled tension-compression mode, as well as a novel phenomenological model which fully predicts the stress-strain material behavior as a function of magnetic flux density, loading frequency and strain. We use a training set of experiments to find the experimentally derived model parameters, from which can predict by interpolation the MRE behavior in a relatively large continuous range of frequency, strain and magnetic field. We also challenge the model to make extrapolating predictions and compare to additional experiments outside the training experimental data set with good agreement. Further development of this model would allow design and control of engineering structures equipped with tension-compression MREs and all the advantages they offer.We acknowledge funding from the European Research Council grant EMATTER 280078

Implementation of a closed-loop structural control system using wireless sensor networks

Wireless sensor networks have rapidly matured in recent years to offer data acquisition capabilities on par with those of traditional tethered data acquisition systems. Entire structural monitoring systems assembled from wireless sensors have proven to be low cost, easy to install, and accurate. However, the functionality of wireless sensors can be further extended to include actuation capabilities. Wireless sensors capable of actuating a structure could serve as building blocks of future generations of structural control systems. In this study, a wireless sensor prototype capable of data acquisition, computational analysis and actuation is proposed for use in a real-time structural control system. The performance of a wireless control system is illustrated using a full-scale structure controlled by a semi-active magnetorheological (MR) damper and a network of wireless sensors. One wireless sensor designated as a controller automates the task of collecting state data, calculating control forces, and issuing commands to the MR damper, all in real time. Additional wireless sensors are installed to measure the acceleration and velocity response of each system degree of freedom. Base motion is applied to the structure to simulate seismic excitations while the wireless control system mitigates inter-storey drift response of the structure. An optimal linear quadratic regulation solution is formulated for embedment within the computational cores of the wireless sensors. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60230/1/214_ftp.pd

Seismic Improvement and Rehabilitation of Steel Concentric Braced Frames: A Framework-Based Review

The ability of structures to withstand seismic loads is the most important feature of earthquake engineering. Because of their high stiffness and lateral strength, concentrically braced frames (CBF) are one of the most prevalent resisting methods in engineering structures. Under moderate seismic events, CBFs have limited lateral displacement capability, resulting in structural damage and substantial post-earthquake expenses. However, when these constructions are exposed to moderate to severe seismic events, their compression members start to buckle. Buckling these compression members in CBF also reduces ductility and causes hysteresis curve deterioration. As a result, they become brittle and have a limited capacity to dissipate seismic energy. On the other hand, conventional CBF constructions exposed to seismic hazards may display an unacceptable soft-story mechanism, in which drift and damage are localized in a single-story, while all the other stories are comparatively unscathed. Several research works have improved CBF seismic behavior, and different strategies have resulted in seismic improvement. This paper presented an overview of seismic improvement modifications of CBF, which have been studied in the literature. A review of current studies to better understand and analyze CBF behavior is presented

A Fail-safe, Bi-Linear Liquid Spring, Controllable Magnetorheological Fluid Damper for a Three-dimensional Earthquake Isolation System

Building codes governing building design and construction require that loss of human life is not anticipated during a large, infrequently occurring earthquake. However, earthquake-induced damage to the building load carrying components, nonstructural components, including architectural and mechanical systems, and internal equipment or contents, is still expected in code compliant buildings. Recent earthquakes have shown that economic losses are dominated by damage to nonstructural components and contents. Seismic isolation systems, which consist of layers of rubber or friction bearings separating the building from its foundation, are effective in protecting buildings from damage due to horizontal ground shakings. However, recent realistic large-scale earthquake shaking tests have shown that nonstructural components and contents in isolated buildings are susceptible to damage from vertical motions. In this study, a fail-safe, bi-linear liquid spring, controllable magnetorheological (MR) damper is designed, built and tested. The device combines the controllable MR damping in addition to the fail-safe viscous damping and liquid spring features on a single unit serving as the vertical component of the building suspension system itself. The controllable MR damping offers an advantage in the case that the earthquake intensity might be higher than that of the design conditions. The bi-linear liquid spring feature provides two different stiffnesses in compression and rebound modes. The higher stiffness in the rebound mode can prevent a possible overturning of the structure during rocking mode of vibrations.The device can be stacked together along with the traditional elastomeric bearings that are currently used to absorb the horizontal ground motions. In the occasion of an earthquake, it is not only exposed to vertical excitations, but also large residual shear excitations. It has to pass these shear forces between the ground and isolated structure. The theoretical and simulation modeling to overcome this major challenge and achieve other system requirements are presented. In addition, a comprehensive optimization program is developed in ANSYS platform to achieve all design requirements. The fabrication and experimental procedures are discussed. The test results showed that the device performed successfully under the combined axial and shear loadings. To our knowledge, this is the first device that not only can provide large damping and spring forces, but can also operate simultaneously under combined axial and shear loadings. The test results are compared against the theoretical modeling, and the results are discussed

Artificial Intelligence Approach for Seismic Control of Structures

Abstract In the first part of this research, the utilization of tuned mass dampers in the vibration control of tall buildings during earthquake excitations is studied. The main issues such as optimizing the parameters of the dampers and studying the effects of frequency content of the target earthquakes are addressed. Abstract The non-dominated sorting genetic algorithm method is improved by upgrading generic operators, and is utilized to develop a framework for determining the optimum placement and parameters of dampers in tall buildings. A case study is presented in which the optimal placement and properties of dampers are determined for a model of a tall building under different earthquake excitations through computer simulations. Abstract In the second part, a novel framework for the brain learning-based intelligent seismic control of smart structures is developed. In this approach, a deep neural network learns how to improve structural responses during earthquake excitations using feedback control. Abstract Reinforcement learning method is improved and utilized to develop a framework for training the deep neural network as an intelligent controller. The efficiency of the developed framework is examined through two case studies including a single-degree-of-freedom system and a high-rise building under different earthquake excitation records. Abstract The results show that the controller gradually develops an optimum control policy to reduce the vibrations of a structure under an earthquake excitation through a cyclical process of actions and observations. Abstract It is shown that the controller efficiently improves the structural responses under new earthquake excitations for which it was not trained. Moreover, it is shown that the controller has a stable performance under uncertainties