Condition Assessment of an In-Service Pendulum Tuned Mass Damper

The performance of passive tuned mass dampers (TMDs) has generally been assessed by parametric studies using numerical models, primarily with the purpose of selecting optimal damper parameters. Alternatively, limited full-scale and experimental verifications of the performance of TMDs have been undertaken; however, these have the inherent shortcoming of not being able to accurately quantify the performance of the TMD to the same excitation time history. Therefore, a hybrid approach is proposed, where the modal characteristics of a full-scale structure equipped with a pendulum TMD (PTMD) are determined through a measurement program and system identification. Subsequently, the responses of a numerical model with natural frequencies, primary mode shapes, and modal damping ratios consistent with the full-scale structure are found using excitation data gathered from a boundary layer wind tunnel by the high frequency base balance (HFBB) method, commonly used to predict the responses of structures through wind tunnel studies. Using a Lagrangian approach, the equations of motion for a three-dimensional PTMD coupled with a flexible main structure are determined, and the time-domain HFBB method is adapted to accommodate the directional coupling of the non-linear, three-dimensional PTMD, where both the planar and spherical motion of the auxiliary mass is considered. The results are compared to the responses predicted using simplistic models excited by broadband white noise, where motion of the tuned mass is linearized to the planar direction. The findings demonstrate the value of passive PTMDs, shed new light on the effect of using simplistic models to predict their performance, and demonstrate a practical approach to quantifying PTMD performance using full-scale measurement data.