Analysis of uniformly and linearly distributed mass dampers under harmonicand earthquake excitation

The effectiveness of multiple mass dampers has been investigated by Igusa a nd Xu [Dynamic characteristics of multiple tuned mass substructures with cl osely spaced frequencies. Earthq. Engng Struct. Dynam. 21 (1991) 1050-70], Yamaguchi and Harnpornchai [Fundamental characteristics of multiple tuned m ass dampers for suppressing harmonically forced oscillations. Earthq. Engng Struct. Dynam. 21 (1993) 51-62], Abe and Fujino [Dynamic characterization of multiple tuned mass dampers and some design formulas. Earthq. Engng Stru ct. Dynam. 23 (1993) 813-35] and Kareem and Kline [Performance of multiple mass dampers under random loading. J. Struct. Engng 121 (1995) 348-61]. In this paper, we extend the results of these previous investigations to exami ne the performance of uniformly and linearly distributed multiple mass damp ers, respectively. These systems were selected to ascertain whether the dis tribution of masses located close to the central mass damper would influenc e the performance of the entire system in reducing vibration. We evaluate p erformance numerically through assessing the effectiveness and robustness o f each system, as well as considering the effects of redundancy, under harm onic excitation. In this regard, we evaluate the performance of the system when certain individual dampers do not function. We show that the uniformly distributed mass system is more effective in reducing the peak dynamic mag nification factor. The linearly distributed system is more robust under mis tuning. It is more robust to damping variation for low damping values but t he effectiveness of the two systems converges as damping increases. The uni formly distributed system is slightly more reliable when an individual damp er fails. The eleven mass system is optimum for both configurations for har monic excitation. The Il-mass system is more effective in structural vibrat ion decay in both cases for the El Centro earthquake simulation. (C) 2001 E lsevier Science Ltd. All rights: reserved.