Ging Long Lin

A Theoretical Study on Piezoelectric Smart Isolation System for Seismic Protection of Equipment in Near-fault Areas

In order to enhance the efficiency and safety of seismic isolation for equipment subjected to near-fault earthquakes that usually possess a long-period pulse-like waveform, a semi-active isolation system named piezoelectric smart isolation system (PSIS), composed of a sliding isolation platform and a piezoelectric friction damper (PFD), is proposed in this study. By controlling the embedded piezoelectric actuator with a DC voltage, the friction force of the PFD can be regulated; therefore, the PFD is able to provide a supplemental damping, which is controllable by a predetermined control law, for the PSIS system. In order to evaluate its isolation performance, the seismic responses of the PSIS was simulated numerically, and the isolation performance of the PSIS was also compared with those of a passive and an active isolation system. The results of these comparisons are discussed in this study. The simulation result has shown that the PSIS can prevent both the excessive isolator displacement and equipment acceleration induced by the long-period pulse component of a near-fault earthquake.

A Unified Analysis Model for Energy Dissipation Devices Used in Seismic Structures

To date, various types of energy dissipation devices (EDDs) have been invented and applied to structural systems for mitigating their seismic responses. An elastic structure with EDDs can be treated as a nonlinear dynamic system with hysteretic property. Due to the diversity of the hysteretic properties of various EDDs, it is difficult to obtain a generic analysis method that can be applied to structures with different EDDs. In this study, a unified analysis model containing an internal variable is proposed for simulating the hysteretic behavior of various types of EDDs. By assigning different physical meanings to the internal variable, the model is able to simulate 3 types of widely used EDDs; namely, yielding, viscoelastic, and friction dampers. The unified model is also able to simulate nonlinear viscous dampers whose velocity terms have an exponential coefficient not equal to 1.0. Furthermore, based on this model, this article also developes a numerical analysis method derived from the discrete-time solution of a state-space equation. Without requiring iteration at each computational time step, the numerical method is able to accurately simulate the hysteretic properties of the 3 kinds of EDDs. The accuracy and efficiency of the proposed analysis method is investigated by using the analytical solution of a nonlinear system governed by Duffings equation, and also by using a seismic structure equipped with multiple EDDs.

Fuzzy Friction Controllers For Semi-active Seismic Isolation Systems

Some studies have shown that a conventional seismic isolation system may suffer from an excessive isolator displacement when subjected to a near-fault earthquake that usually has a long-period velocity pulse waveform. In order to alleviate this problem, a semi-active isolation system (SAIS) with a variable friction damper (VFD) controlled by proposed fuzzy controllers is investigated in this study. By varying the clamping force in the VFD damper, the slip force of the damper applied on the isolation system can be regulated on-line. Moreover, in order to determine the clamping force, four types of simple fuzzy controllers are developed based on the concept of antilock braking systems used in automobiles, and their isolation performances are simulated and compared. In addition, in order to assure a fair comparison, four types of earthquakes, namely far-field, weak near-fault, strong near-fault, extreme near-fault earthquakes, representing a wide variety of ground motions are considered as the ground excitations in the simulation. The numerical result shows that among the four fuzzy controllers proposed, the one that takes the ground velocity as an input variable has the best overall performance. As compared to the uncontrolled passive isolation system, the SAIS system with this controller greatly reduces the structural acceleration and base displacement responses simultaneously in a strong or extreme near-fault earthquake, whereas the controller results in a roughly equal level of acceleration response and a much less base displacement in a far-field or weak near-fault earthquake.

Fuzzy Logic Controllers for a Seismic Isolation System with Variable Friction Damper

Protecting a seismic isolated building from the attack of near-fault earthquakes is a challenge, because a near-fault earthquake usually contains strong long-period components, which are significantly different from a regular earthquake. Conventional seismic isolation systems, such as sliding or elastomeric bearing systems, may induce excessive isolator drift in a near-fault earthquake. To overcome this problem, current practice usually adopts supplementary passive damping in the isolation system. Nevertheless, due to its passive nature, the parameters of a passive damper can not be adjusted online, so the damper may not perform well when it is subjected to an earthquake significantly different from the one that the damper is designed for. In order to improve the performance of seismic isolation in near-fault areas, this study investigates the possible use of a fuzzy logic controlled variable friction damper (VFD) in a sliding isolation system. Four types of fuzzy controllers were studied numerically for the control of the VFD, and their resulting isolation performances in both near-fault and far-field earthquakes with various earthquake intensities are compared and highlighted. It is demonstrated that by properly selecting the fuzzy control law, the isolator drift induced by a near-fault earthquake can be significantly suppressed, without sacrificing the isolation efficiency.