Kwan-Soon Park

Minmax optimum design of active control system for earthquake excited structures

A minmax optimization method for the vibration control system considering uncertain dynamics is presented in this paper. In the proposed method, structural modeling errors and various excitations, which may cause performance degradation, are treated as plant parameters. The minmax problem considered in this study is not only to find an optimal controller that minimize structural responses but also to search the worst-case plant parameters that maximize structural responses, whereas the conventional optimal design usually deals with a minimization problem for a certain performance index. In order to solve the proposed minmax problem, the bimatrix co-evolution algorithm is adopted. It approximates the minmax problem as the bimatrix game between two fitness measures and finds the optimal solution effectively through the co-evolutionary process, as a result, the optimal controller and the worst-case plant parameters are searched simultaneously. Example design of an earthquake-excited building structure with active tendon control system is performed and comparative results of numerical simulation are presented to validate the proposed method.

Robust Performance of Fuzzy Supervisory Control for Seismically Excited Cable-Stayed Bridge

This paper investigates the robust performance of fuzzy supervisory control (FSC) technique for seismically excited cable-stayed bridge. The FSC technique utilizes fuzzy logic-based decision-making process to incorporate a set of pre-designed static control gains into a time-varying optimal control gain. To demonstrate the excellent robustness of the FSC technique on response control of earthquake-excited cable-stayed bridge, a conventional linear quadratic Gaussian (LQG) controller with single static gain and two fuzzy supervisory controllers are designed for the benchmark cable-stayed bridge, and their robust performances are examined under uncertainty in bridge model and against failures in actuators and sensors. Under the presence of uncertainty in the bridge model, the FSC system successfully reduces the seismic responses of the bridge without significant increase in the total amount of power and stroke required by the control system, while the LQG system exhibits a substantial increase in the seismic responses. Under conditions of sensor or actuator failures, the FSC system guarantees a more enhanced robust performance than the LQG system as well.

Preference Based Genetic Algorithm for the Optimum Design of Integrated Structural Control System

This paper proposes an optimal design of a hybrid system for the mitigation of wind-induced vibration in high-rise buildings. Even if effective control performance can be achieved by the hybrid system which applies simultaneously both active and passive control devices, its design is extremely complicated due to the increase of the design variables. This paper considers a hybrid system composed of hybrid mass damper and viscous dampers. The corresponding design variables are the mass, tuning ratio, damping ratio, damper locations and capacity of the dampers. Since the minimization of cost factors is also a matter of utmost importance, the required control efforts and dynamic responses of the target structure are selected as objective functions to be minimized. Therefore, the problem is formulated as a multi-objective optimization problem involving the design of two different types of systems. The validity of the proposed optimization technique is verified through a wind-excited 20-story building with hybrid control system and comparative results with non-hybrid design approach are presented.

Analysis of soil-structure interaction considering complicated soil profile

The effect of soil-structure interaction (SSI) is an important consideration and cannot be neglected in the seismic design of structures on soft soil. Various methods have been developed to consider SSI effects and are currently being used. However, most of the approaches including a general finite element method cannot appropriately consider the properties and characteristics of the sites with complicated soil profiles. To overcome these difficulties, this paper presents soil-structure interaction analysis method, which can consider precisely complicated soil profiles by adopting an unaligned mesh generation approach. This approach has the advantages of rapid generation of structured internal meshes and leads to regular and precise stiffness matrix. The applicability of the proposed method is validated through several numerical examples and the influence of various properties and characteristics of soil sites on the response is investigated.

Evaluation of Robust Performance of Fuzzy Supervisory Control Technique

This paper describes the robust performance of fuzzy supervisory control (FSC) approach for the seismic response control of cable-stayed bridges. FSC is a hybrid control method with the hierarchical structure of several sub-controllers and fuzzy supervisor. Each sub-controller is preliminarily designed to reduce the selected response of the structure only, and a fuzzy supervisor is introduced to improve the overall control performance by modulating the predesigned static gains into time-varying dynamic gains. To demonstrate the robust performance of the proposed strategy, the FSC and linear quadratic Gaussian (LQG) controller are optimally designed and their seismic performances are compared according to the variation of the bridge stiffness in the phase I benchmark control problem. The comparative results show that the FSC system can clearly guarantee the robust performance against the uncertainties of the bridge model.

Evaluation of seismic performance and effectiveness of multiple slim-type damper system for seismic response control of building structures.

This paper presents the evaluation of seismic performance and cost-effectiveness of a multiple slim-type damper system developed for the vibration control of earthquake excited buildings. The multiple slim-type damper (MSD) that consists of several small slim-type dampers and linkage units can control damping capacity easily by changing the number of small dampers. To evaluate the performance of the MSD, dynamic loading tests are performed with three slim-type dampers manufactured at a real scale. Numerical simulations are also carried out by nonlinear time history analysis with a ten-story earthquake excited building structure. The seismic performance and cost-effectiveness of the MSD system are investigated according to the various installation configurations of the MSD system. From the results of numerical simulation and cost-effectiveness evaluation, it is shown that combinations of the MSD systems can effectively improve the seismic performance of earthquake excited building structures.