An experimental and analytical study is made of the performance of particle dampers under wide-band random excitation. A small model, provided with a nonlinear auxiliary mass damper, was used to investigate the major system parameters that influence the performance of particle dampers: total auxiliary mass ratio, particle size, container dimension, and the intensity and direction of the excitation. It is shown that properly designed particle dampers, even with a relatively small mass ratio, can considerably reduce the response of lightly damped structures. An approximate analytical solution, which is based on the concept of an equivalent single unit-impact damper, is presented. It is shown that the approximate solution can provide an adequate estimate of the root-mean-square response of the randomly excited primary system when provided with a particle damper that is operating in the vicinity of its optimum range of parameters.

This article presents an experimental study of the performance of particle dampers under harmonic excitation. The effects of various system parameters—including particle size, container dimensions, intensity, and frequency of excitation—were investigated using a single degree-of-freedom building model under harmonic base excitation. It is shown that particle dampers, even with a small mass ratio, can be very effective in attenuating the vibrations of lightly damped structures. An approximate method is provided to estimate, with reasonable accuracy, the response of a harmonically excited structure that is equipped with a particle damper operating in the vicinity of the optimum range of its system parameters. NOMENCLATURE dx = separation of the walls of the damper that are perpendicular to the direction of the excitation dy = separation of the walls of the damper that are parallel to the direction of the excitation dz = maximum height that the balls can reach (depth of particle container) e = square root of the summation of the variations of the response e f -variation of the response corresponding to a discrete frequency ratio M = mass of the primary structure m -total mass of the particles in the multiparticle damper ' so = amplitude of the harmonic excitation x; = amplitude of the response of structure with an attached single-particle damper x; = amplitude of the response of structure with an attached multiparticle damper = ratio of critical damping of the primary system ~ .

The fundamental period is one of the most critical parameters for the seismic design of structures. There are several literature approaches for its estimation which often conflict with each other, making their use questionable. Furthermore, the majority of these approaches do not take into account the presence of infill walls into the structure despite the fact that infill walls increase the stiffness and mass of structure leading to significant changes in the fundamental period. In the present paper, artificial neural networks (ANNs) are used to predict the fundamental period of infilled reinforced concrete (RC) structures. For the training and the validation of the ANN, a large data set is used based on a detailed investigation of the parameters that affect the fundamental period of RC structures. The comparison of the predicted values with analytical ones indicates the potential of using ANNs for the prediction of the fundamental period of infilled RC frame structures taking into account the crucial parameters that influence its value.

SUMMARYThis paper presents the results of an experimental and analytical study of the performance of granular material dampers with tungsten powder, as an impacting mass, under wide-band random excitation. The influence of some of the major system parameters such as the total auxiliary mass ratio, container dimensions and intensity of the excitation are investigated using a small building model under base excitation. An approximate analytical solution based on the concept of an equivalent single-unit impact damper is presented. Comparison between the experimental and analytical results shows that, with the proper use of the equivalent single-particle impact damper approach, reasonably accurate estimates of the rms response of a primary system under stationary random excitation can be obtained.

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