Mai Tong

Optimized Damping Device Configuration Design of a Steel Frame Structure Based on Building Performance Indices

Energy dissipation devices (EDDs) have been accepted as one of the viable strategies for enhancing the seismic performance of building structures. However, the current design provisions do not provide guidelines for optimizing the EDD configurations on structures. For many building structures an efficient configuration of EDDs may provide considerable performance improvement. Similarly, an optimized configuration may reduce the number of EDDs required to achieve a target performance objective. In this paper an existing building with added linear viscous dampers is redesigned based on different performance index optimization. The results indicate that the optimal device configurations are highly related to the dynamic properties of the structure and its required performance index. In one instance, where the cost is the major concern and a performance requirement is placed on story drift limitation, the total device damping coefficient can be reduced by 26%.

Dynamic responses under the excitation of pulse sequences

This paper studies the dynamic responses of SDOF system under pulse-dominant excitations. The purpose of the study is to prepare for scrutiny of some near-field pulse-dominant ground motions and their potential to cause structural damage. Extending the single pulse dynamics, we consider the effect of pulse sequences. This kind of excitation was particularly obvious in some of previous earthquakes such as Northridge (1994) and Chi-Chi (1995). Based on the duration, peak and rise and decay era of the main pulse as well as its relationship with the predecessor and successor pulses, we propose a classification for the pulse sequences. Consequent studies have been carried out for acceleration, velocity and displacement response spectra of the main pulse with either a predecessor or a successor pulse. The analysis also includes general response behaviors in different fundamental period segments and special aspects of response at certain points (e.g., the corresponding peak points).

A real-time structural parameter modification (RSPM) approach for random vibration reduction: part I, principle

Earthquake-induced structural vibrations are stochastic in nature. Part I of this study presents a novel structural control methodology for earthquake vibration reductions. It summarizes the efforts of the authors toward the development of RSPM control between 1993 and 1996. The operating control principle is minimization of conservative energy. The control hierarchy is realized by low-power-consuming devices (functional switches) with multiple ranked loops. The control method is to adjust optimally the physical parameters (mass, damping and stiffness) of the structure in real time. This method is therefore described as real-time structural parameter modification (RSPM). It may be called variable passive control or parametric control. The basic thesis of RSPM is presented, together with a discussion of the minimal principle of conservative energy of a vibrating system and the RSPM control hierarchy which contains four ranked loops. Variable passive control is capable of handling the stochastic nature of earthquake ground motion and it does not have certain major drawbacks of conventional active control methods. Part II of this study will describe the experimental verifications of RSPM. It will be shown that RSPM can dissipate considerably more energy than existing passive energy dissipation devices. In addition, RSPM can reduce vibrations resulting from multi-directional excitations.

A real-time structural parameter modification, approach for random vibration reduction: Part II. Experimental verification

Abstract Earthquake induced structural vibrations are stochastic in nature. In this paper, we present a novel structural control methodology for earthquake vibration reductions in two parts. Part I summarizes the efforts of the authors toward the development of real-time structural parameter modification (RSPM) control between 1993 and 1996. The operating control principle is minimization of conservative energy. The control hierarchy is realized by low-power-consuming devices (functional switches) with multiple ranked loops. The control method is to optimally adjust the physical parameters (mass, damping and stiffness) of the structure in real time. This method is therefore described as RSPM. It may be called variable passive control or parametric control. In Part I of this paper, the basic thesis of RSPM is presented, together with a discussion of the minimal principle of conservative energy of a vibrating system and the RSPM control hierarchy which contains four ranked loops. Variable passive control is capable of handling the stochastic nature of earthquake ground motion and it does not have certain major drawbacks of conventional active control methods. Part II of this paper describes experimental verifications of RSPM. It will be shown that RSPM can dissipate considerably more energy than existing passive energy dissipation devices. In addition, RSPM can reduce vibrations resulting from multidirectional excitations.

An Off-and-Towards-Equilibrium Strategy for Vibrational Control of Structures

Traditional control strategies have difficulty handling nonlinear behavior of structures, time variable features and parameter uncertainties of structural control systems under seismic excitation. An off-and-towards-equilibrium (OTE) strategy combined with fuzzy control is presented in this paper to overcome these difficulties. According to the OTE strategy, the control force is designed from the viewpoint of a mechanical relationship between the motions of the structure, the exciting force and the control force. The advantage of the OTE strategy is that it can be used for a variety of control systems. In order to evaluate the performance of the proposed strategy, the seismic performance of a three-story shear building with an Active Tendon System (ATS) using a Fuzzy Logic Controller (FLC) is studied. The main advantage of the fuzzy controller is its inherent robustness and ability to handle any nonlinear behavior of structures. However, there are no design guidelines to set up the corresponding control rule table for a FLC. Based on the proposed strategy for the FLC, a control rule table associated with the building under study is developed, which then allows formation of a detailed algorithm. The results obtained in this study show that the proposed strategy performs slightly better than the linear quadratic regulator (LQR) strategy, while possessing several advantages over the LQR controller. Consequently, the feasibility and validity of the proposed strategy are verified.

Hybrid response control of closely spaced buildings

Publisher Summary Seismic retrofit of buildings in urban centers often encounters the challenge of limiting the displacement between closely spaced buildings in addition to acceleration reduction. Recent advances in energy dissipation technologies have enabled structural engineers to control deformational responses to desired levels. A combined realtime structural parameter modification (RSPM) and passive damping control system approach takes advantage of the RSPM effectiveness in reducing displacement and acceleration by passive damping. It can be used to effectively reduce the displacement and acceleration. By optimizing the control parameter, the roof displacement of a building can be reduced effectively and the acceleration response can also be controlled at the same time. Inelastic response analysis indicates that the combined RSPM and passive damping hybrid control system can have 20% more response reduction for 15% damping and 30% stiffness level. The system has the greatest reduction in the ductility demand range of 5 to 10, which is the life safety performance ductility range for most building structures. In general, the nonlinear stiffness part of the RSPM technology alone can provide damping up to 30%, however the size and capacity are normally balanced with other considerations such as the level of damping and the capacities of the supporting load bearing structural members.

Development of real-time structural parameter modification (RSPM) systems

In recent years the authors have engaged in the development of a special technology to optimally modify a structures physical parameters (mass, damping and stiffness) in time- dependent loading conditions. Specific efforts have been devoted to reduce structural responses under seismic loading. In this regard, there are many other research activities dealing with different devices and control algorithms generally classified in the following categories: passive control, active and hybrid control, adaptive control, semi-active control, etc. All together, this newly emerging field of structural control has generated significant momentum of development. Real-time structural parameter modification (RSPM) is a different approach from the categories mentioned above. A detailed explanation of RSPM is given in the references. In this paper, we discuss a number of fundamental issues facing the development of various structural control technologies. These issues are summarized from our development of RSPM, and are examined based on the view that structural control devices may be considered from only two distinct types: material type and mechanical type. Such a view helps to classify some advantages and disadvantages of different structural protective systems including RSPM.