The practical effects of friction for tuned mass dampers installed in tall buildings

Abstract

In real-world applications, tuned mass dampers (TMDs) possess friction that must be overcome before they will increase the total effective damping of the structure. The performance of structure-TMD systems with unintended TMD friction is investigated in this study. A nonlinear time domain model is developed, which incorporates the TMD damping due to friction, and also exhibits TMD “lock-out” if the forces of friction are not overcome, a feature that existing studies have not considered. Comparisons with full-scale measurements indicate the model adequately captures the response of a TMD with friction. A linearized equivalent mechanical model is also presented, which represents the friction as amplitude-dependent viscous damping, but this model does not capture TMD lock-out. A parametric study is conducted to assess the effect of TMD friction on the performance of TMD systems with various TMD mass ratios, structure and TMD damping ratios, and the TMD damping form (linear or quadratic). In all cases, the TMD performance decreases markedly if the baseline peak structural acceleration is not at least an order of magnitude greater than the acceleration that causes the TMD to break free. If the baseline acceleration is less than five times the break-free acceleration, the TMD motion reduction performance may be negligible, and the linearized model predictions do not agree with the nonlinear simulations. TMD lock-out produces a non-stationary system response, in which the TMD reduces the peak structural accelerations slightly more than the RMS structural accelerations.