Comparative Study on Multi-Objective Genetic Algorithms for Seismic Response Controls of Structures

This chapter introduces three new multi-objective genetic algorithms (MOGAs) for minimum distributions of both actuators and sensors within seismically excited large-scale civil structures such that the structural responses are also minimized. The first MOGA is developed through the integration of Implicit Redundant Representation (IRR), Genetic Algorithm (GA), and Non-dominated sorting GA 2 (NSGA2): NS2-IRR GA. The second one is proposed by combining the best features of both IRR GA and Strength Pareto Evolutionary Algorithm (SPEA2): SP2-IRR GA. Lastly, Gene Manipulation GA (GMGA) is developed based on novel recombination and mutation mechanism. To demonstrate the effectiveness of the proposed three algorithms, two full-scale twenty-story buildings under seismic excitations are investigated. The performances of the three new algorithms are compared with the ones of the ASCE benchmark control system while the uncontrolled structural responses are used as a baseline. It is shown that the performances of the proposed algorithms are slightly better than those of the benchmark control system. In addition, GMGA outperforms the other genetic algorithms.

Optimal Passive Damper Positioning Techniques

A consolidated review of the current-state-of-the-art on optimal damper positioning techniques is presented in this chapter. The inherent assumptions made in previous research are discussed and substantiated with numerical studies. Earlier studies have shown that optimal distribution of dampers is sensitive to in-structure damping. In this chapter the significance of optimal distribution of dampers coupled with the necessity for the use of a more realistic in-structure damping model is qualitatively illustrated using a comparative sensitivity study. The effect of inherent assumption of linearity of the parent frame on the ‘optimality’ is also investigated. It is shown that linearity assumption imposed on the parent frame in a major seismic event may not be justified; thereby raising doubts on the scope of optimality techniques proposed in literature.

Optimal Placement of Viscous Dampers for Seismic Building Design

While the use of supplemental damping for improving the seismic performance of buildings has gained acceptance in recent years, there remains a lack of consensus over how dampers should be optimally arranged within a structure. The authors review recent advances in damper placement methodology based on optimisation theory, and present a detailed comparative study of five selected methods: two using simple empirical rules – uniform and stiffness-proportional damping distributions; and three more advanced, iterative methods – the simplified sequential search algorithm (SSSA), Takewaki’s method based on minimising transfer function drifts, and Lavan’s fully-stressed analysis/redesign approach. The comparison of the selected methods is based on the performance enhancement of a ten-story, steel moment-resisting frame. It is shown that even very crude placement techniques can achieve substantial improvements in building performance. The three advanced optimisation methods show the potential to reduce interstory drifts beyond the level that can be achieved using uniform or stiffness-proportional methods, though the influence on floor accelerations is less marked. The optimisation methods studied show broadly comparable performance, so ease of use becomes a significant factor in choosing between them. In this respect, Lavan’s approach offers some advantages over the others.

Damper Optimization for Long-Span Suspension Bridges

Long-span suspension bridges are becoming prevalent globally with the rapid progress in design methodologies and construction technologies. Although with apparent progress, the balance between excessive displacement and inner forces, under dynamic loads, is still a main concern because of increased flexibility and low structural damping. Therefore, effective controllers should be employed to control the seismic responses to ensure their normal operation. In this chapter, the combination of the analytic hierarchy process (AHP) and first-order optimization method are formulated to optimize seismic response control effect of the Runyang suspension bridge (RSB) under earthquakes, considering traveling wave effect. The compositive optimal parameters of dampers are achieved on the basis of 3-dimensional nonlinear seismic response analyses for the RSB and parameters sensitivity analyses. Results show that the dampers with rational parameters can reduce the seismic responses of the bridge significantly, and the application of the AHP and first-order optimization method can lead to accurate optimization effects.

Nonlinear Structural Control Using Magnetorheological Damper

This chapter provides an introduction to semi active control of base isolated buildings using magnetorheological (MR) dampers. Recently developed nonlinear control algorithms are discussed. First a fuzzy logic control (FLC) is designed to decide how much voltage is required to be supplied to the MR damper for a desired structural response. The FLC is optimized using micro genetic algorithm. A novel geometric approach is developed to optimize the FLC rule base. Experiments are undertaken to access the efficacy of the optimal FLC. Secondly the chapter develops two model based control algorithms based on dynamic inversion and integrator backstepping approaches. A three storey base isolated building is used for experimental and numerical studies. A numerical comparison is shown with clipped optimal control.

Evolutionary Optimization of Passive Compensators to Improve Earthquake Resistance

Compensators are widely used to influence the dynamic response of excited structures. The coupling of additional masses with defined stiffness and damping to the vibrating elements reduces or avoids unwanted oscillations. In earthquake engineering, compensators often consist of one or a small number of such additional mass-spring combinations. To come up with a good design of the compensators, a multidimensional optimization problem has to be solved. As there might be many local optima, evolutionary approaches are the appropriate choice of the optimization strategy. They start with some basic designs. Then a sequence of generations of design variants is studied. The members of each generation are derived from the parent generation by crossing and mutation. The best kids are the parents of the next generation. Optimization results show that the use of compensating systems may essentially reduce the impact of an earthquake.

Neuromorphic Smart Controller for Seismically Excited Structures

In this chapter, an application of a neuromorphic controller is proposed for hazard mitigation of smart structures under seismic excitations. The new control system is developed through the integration of a brain emotional learning-based intelligent control (BELBIC) algorithm with a proportional-integral-derivative (PID) compensator and a clipped algorithm. The BELBIC control is based on the neurologically inspired computational model of the amygdala and the orbitofrontal cortex. A building structure employing a magnetorheological (MR) damper under seismic excitations is investigated to demonstrate the effectiveness of the proposed hybrid clipped BELBIC-PID control algorithm. The performance of the proposed hybrid neuromorphic controller is compared with the one of a variety of conventional controllers such as a passive, PID, linear quadratic Gaussian (LQG), and emotional control systems. It is shown that the proposed hybrid neuromorphic controller is effective in improving the dynamic responses of structure-MR damper systems under seismic excitations, compared to the benchmark controllers.

Multi-Objective Optimization Design of Control Devices to Suppress Tall Buildings Vibrations against Earthquake Excitations Using Fuzzy Logic and Genetic Algorithms

The main objective of this chapter is to find the optimal values of the parameters of the base isolation systems and that of the semi-active viscous dampers using genetic algorithms (GAs) and fuzzy logic in order to simultaneously minimize the buildings’ selected responses such as displacement of the top story, base shear, and so on. In this study, performance of base isolation systems, and semi-active viscous dampers are studied separately as different vibration control strategies. In order to simultaneously minimize the objective functions, a fast and elitist non-dominated sorting genetic algorithm (NSGA-II) approach is used to find a set of Pareto-optimal solution. To study the performance of semi-active viscous dampers, the torsional effects exist in the building due to irregularities, and unsymmetrical placement of the dampers is taken into account through 3D modeling of the building.

Optimum Design of a New Hysteretic Dissipater

In this chapter, a new seismic protection device is proposed. It is designed to dissipate the energy entering a structure subject to seismic action through the activation of hysteresis loops of the material that composes it. These devices are characterized by a high capacity to absorb the seismic energy and the ability to concentrate the damage on it and, consequently, to keep the structure and the structural parts undamaged. Moreover, after a seismic event they can be easily replaced. In particular, this chapter proposes a new shear device that shows the plasticity of some areas of the device at low load levels. In order to maximize the amount of dissipated energy, the design of the device was performed by requiring that the material be stressed in an almost uniform way. In particular, the device is designed to concentrate energy dissipation for plasticity in the aluminum core while the steel parts are responsible to make stiffer the device, limiting out-of-plane instability phenomena. The geometric configuration that maximizes the energy dissipation has been determined using a structural optimization routine of finite element software.

Effective Configurations of Active Controlled Devices for Improving Structural Seismic Response

Improving structural seismic response using dampers became a widely used method in the recent decades. Various devices were developed for seismic protection of structures and appropriate methods were proposed for effective design of control systems. An actual problem is how many dampers should be used as is their optimal location for yielding the desired structural response with minimum cost. A method for finding effective dampers’ placement and using amplifiers for dampers connection was recently proposed in the literature. The current study presents analyses of the amplification and placement of active controlled devices on the efficiency of a control system. A model of a twenty-story structure with active control systems including different dampers configurations is simulated. The response of the structure to natural earthquake excitations is also reported. The results of this study show a method of selecting proper configuration of active devices allowing cost effective control.