Vibration control identification of seismically excited m.d.o.f. structure-PTMD systems

In this paper, the vibration control philosophy and optimal design of passive tuned mass dampers (PTMDs) for a multi-degree-of-freedom (m.d.o.f.) structure are presented. In order to prove the effectiveness of PTMD, the modal properties of a m.d.o.f. building with an optimal PTMD are identified using a specified system identification procedure. The difference in the modal properties between a structure with and without PTMD determines the PTMD vibration control performance. An extended random decrement method, which considers the measurement correlation, was first employed to reduce the measured dynamic responses of the building. The Ibrahim time domain technique was then applied to calculate the modal frequencies, damping ratios, and mode shapes based on only a few floor response measurements. To obtain the complete mode shapes, an interpolation method was developed to estimate the mode shape values for the locations without measurements. The seismic responses at floors with and without measurements were also calculated. Numerical results throughout a five-storey building under ambient random excitations demonstrated that the proposed system identification techniques are able to identify the dominant modal parameters of the system accurately, even with high closed-space frequencies and noise contamination. In addition, PTMD was proved to be a useful control device. (C) 2001 Academic Press.