Civil Engineering Association

1) Semiactive control of friction dampers
Abstract :
Semi!active control of friction dampers has been proposed to improve the energy dissipation characteristics of passive friction dampers and to broaden the areas of application in which they can successfully be used[ In this paper\ we propose control laws for friction dampers which maximize energy dissipation in an instantaneous sense by
modulating the normal force at the friction interface[ In particular\ we consider the effect of displacement! and velocity!induced friction dynamics on the design of the control law[ A dynamic controller is proposed that prevents stored frictional energy from being returned to the system[ Using both simulation and experimental results\ we demonstrate under what operating conditions friction dynamics are vital to the control problem and\ for these
conditions\ demonstrate the e.cacy of the proposed controller[ Furthermore\ the experiments reveal that control strategies which\ unlike instantaneous optimization\ take system dynamics into account could lead to significant additional improvements in energy dissipation.

2) Semi-active control of a building complex with variable friction dampers
Abstract :
Semi-active coupling control of a building complex, which consists of a main building and a podium structure, using variable friction dampers is investigated in this paper for mitigating seismic responses. The mathematical model of a building complex with variable friction dampers under earthquake excitation is first established. A clipped control strategy is then developed to allow variable friction dampers to work effectively with linear quadratic Gaussian control algorithms as a global-feedback controller. Local-feedback controllers, which include viscous and Reid friction controllers, modulated homogeneous friction controllers, and non-sticking friction controllers, are also formulated for use with variable friction dampers. A building complex of a 20-story main building and a 3-story podium structure is finally used as a numerical example to demonstrate the effectiveness of semi-active coupling control and to compare the local-feedback controllers with the global-feedback controller. The control performance of each controller for the building complex with either single or multiple friction dampers under various ground motions is examined in terms of both story drifts and acceleration responses. The numerical results show that semi-active coupling control is quite promising for reducing seismic responses of both buildings.

3) Seismic analysis of structures connected with friction dampers
Abstract :
Analytical seismic responses of two adjacent structures, modeled as single-degree-of-freedom (SDOF) structures, connected with a friction damper are derived in closed-form expressions during non-slip and slip modes and are presented in the form of recurrence formulae. However, the
derivation of analytical equations for seismic responses is quite cumbersome for damper connected multi-degree-of-freedom (MDOF) structures as it involves some dampers vibrating in sliding phase and the rest in non-sliding phase at any instant of time. To overcome this difficulty, two numerical models of friction dampers are proposed for MDOF structures and are validated with the results obtained from the analytical model considering an example of SDOF structures. It is found that the proposed two numerical models are predicting the dynamic behavior of the two connected SDOF structures accurately. Further, the effectiveness of dampers in terms of the reduction of structural responses, namely, displacement, acceleration and shear forces of connected adjacent structures is investigated. A parametric study is also conducted to investigate the optimum slip force of the damper. In addition, the optimal placement of dampers, rather than providing dampers at all floor levels is also studied to minimize the cost of dampers. Results show that using friction dampers to connect adjacent structures of different fundamental frequencies can effectively reduce earthquake-induced responses of either structure if the slip force of the dampers is appropriately selected. Further, it is also not necessary to connect two adjacent structures at all floors but lesser dampers at appropriate locations can significantly reduce the earthquake response of the combined system.

4) Integrated vibration control and health monitoring of building structures
using semi-active friction dampers: Part II —Numerical investigation
Abstract
An integrated procedure for model updating, vibration control and damage detection of a building structure using semi-active friction dampers has been presented in part I of this paper. The feasibility of the proposed procedure and the practical issues of its application are investigated numerically in this accompanying paper. The model updating scheme is first applied to an example building to identify its structural parameters. The effects of measurement noise, incomplete measurement information and damper stiffness on the quality of model updating are evaluated. The control performance of seismic response of the example building using the semi-active friction dampers manipulated by a local feedback control strategy with a Kalman filter is then assessed through comparisons with the same local feedback control strategy but without the Kalman filter and with a global feedback control strategy. The optimum damper stiffness suitable for both model updating and vibration control is also determined. Finally, two damage scenarios are presented to ascertain the accuracy of the damage detection scheme for different damage severities and locations with and without noise contamination. The additional comparison is made between the proposed damage detection scheme and the traditional sensitivity approach. The numerical results demonstrate the feasibility of the proposed integrated procedure.

5) Integrated vibration control and health monitoring of building structures
using semi-active friction dampers: Part I—methodology
Abstract
Vibration control and health monitoring of building structures subjected to harsh environments have been actively investigated in recent years. Nevertheless, in most investigations the two aspects have been treated separately. This paper presents an integrated procedure for vibration control
and health monitoring of a building structure using semi-active friction dampers. The concept of an integrated system using semi-active frictiondampers is first introduced. A scheme based on adding a known stiffness by using semi-active friction dampers is then presented to update the stiffness and mass matrices of the building and to identify its structural parameters. Based on the updated system matrices, the control performanceof semi-active friction dampers using local feedback control with a Kalman filter is investigated for a building subjected to earthquake excitation. By assuming that the building suffers certain damage after extreme events or long service and by using the previously identified original structural parameters, a damage detection scheme based on adding a known stiffness using semi-active friction dampers is proposed and used for damage detection. The feasibility and accuracy of the proposed integrated procedure will be demonstrated in Part II of this paper through detailed numerical examples and parametric studies.

6) Feasibility study of a tunable friction damper
Abstract
A new design of friction damper is proposed and called the tunable friction damper. The design is
proposed as an alternative to a conventional sliding mass-type friction damper, which is commonly used to reduce vibration in rotating systems. The design combines advantages of the friction damper, which dissipates energy via sliding friction, and the spring-mass-type vibration damper, which absorbs energy by its own vibration. The tunable damper is designed to work as a friction damper while the mass slips and as a vibration absorber while the mass sticks, during which the conventional friction damper ceases to function as a damper. The most important advantage of the design is that the damper can be tuned for a large reduction of the vibration in a narrow frequency range of choice while providing damping in a broad range of frequency as well. Despite its simple concept, design analysis of the system is difficult due to the nonlinear dynamics of the system. Numerical simulations are employed to demonstrate the feasibility of the concept, and to understand the roles of major design parameters. It is shown that proper sizing of the mass and the compliance of the damper allows the design to exploit benefits of both the friction damper and vibration absorber.

All 6 papers in single 11.6MB rar file