Vibration control of structures with viscoelastic dampers

Abstract

This dissertation is concerned with improvement and identification of the mathematical model for viscoelastic dampers, development of analytical methods for structures with such dampers, design of damping devices for horizontal and vertical vibration control and their application to building structures. Experimental investigations on the selected viscoelastic dampers have been carried out. The hysteresis loops of such dampers under different excitation conditions have been found and their associated equivalent stiffness, damping ratio and energy dissipation ability have been determined. Based on the review of the commonly used mathematical models for viscoelastic dampers and the dynamic characteristics obtained in the experimental studies, the fractional derivative model has been chosen and improved to describe the dynamic behaviours of viscoelastic dampers. To evaluate the parameters of the proposed model, two kinds of identification method which can facilitate the use of all test data simultaneously in the identification process have been developed. Parameter values of the proposed model for the two selected dampers have been obtained by the developed methods. By comparison between the hysteresis loops derived from the proposed model and the corresponding loops of the tested results, and also those derived from the commonly used Kelvin-Voigt model, it has been found that the proposed model can well describe the dynamic behaviours of various viscoelastic dampers, and is more versatile and can be used more widely for various kinds of viscoelastic damper than the Kelvin-Voigt model. Moreover, parametric studies on the proposed mathematical model have been carried out and the features of the model have been discussed in detail. Two schemes for modelling viscoelastic dampers in the structural response analysis have been proposed. An analytical method in time domain in association with the modelling schemes has been developed. Since the proposed model has simple expression in frequency domain, an analytical method in hybrid time-frequency domain has also been developed. This method can save more computing time than the method in time domain and can be used for structures subject to not only sinusoidal excitation, but also random excitation like seismic loading. In addition, the damping matrix of structures incorporated with viscoelastic dampers can be obtained by the proposed analytical methods, which is useful for carrying out dynamic analysis with other commercial software packages. A practical damping device has been designed for horizontal vibration control of framed structures. It has been proved experimentally that such damping device is effective in attenuating horizontal vibration. By comparison of experimental and analytical results, the proposed analytical methods for predicting the dynamic responses of structures incorporated with such damping devices have been verified. A large amount of numerical simulation work with various parameters has been carried out on a multi-story building structure. Some useful guidelines for practical design of horizontal vibration control with such damping devices have been obtained. To control vertical vibrations of long span structures, a beam-column connection incorporated with viscoelastic dampers has been proposed. Great effectiveness in control the vertical vibration of beam structures can be achieved, which has been demonstrated by the experimental tests carried out on a long span beam with such beam-column connections. Comparisons between the analytical results and the experimental results have been made with which the analytical methods have been verified. Numerical simulation has been carried out on a real long span beam with and without such beam-colunn connections. The effects of various parameters on vertical vibration control have been studied and useful design guidelines for the design of vibration control for long span structures with the proposed beam-column connections have been drawn.