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In recent years, the use of Tuned Mass Damper (TMD) to reduce
the dynamicresponses of structures under strong environmental
loadings has become an area of considerable research interest.
To design an optimum TMD requires the prior knowledge of modal
properties of the controlled structure. For a real building
structure, the lateral and torsional motions are coupled if the
centers of mass and resistance do not coincide. Therefore, it is
of great importance and necessity that system identification of
torsionally-coupled buildings using real response measurements
be carried out in conjunction with the design of optimal TMDs.
In the first part of this thesis, a system identification
technique is developed to evaluate the modal parameters of
irregular buildings, modeled astorsionally-coupled buildings,
based only on few floor earthquake response records. First, a
modified random decrement technique is employed to reduce the
floor response data to extract their corresponding free
vibration responses.Then, the Ibrahim time domain technique is
applied to calculate the structural modal frequencies, damping
ratios and mode shapes. Because of using only partial floor
response measurements, a mode shape interpolation method is also
developed to estimate the mode shape values for the locations
without measurement. The results through simulation data of a
five-story building under 1940 El Centro bi-directional
earthquakes and real records of a seven-story building in I-Lan,
Taiwan due to 1994 Nan-Au earthquake (M=6.2) show that the
proposed system identification technique is capable of
identifying structural dominant modal parameters and responses
accurately even with highly-coupled modes and high level of
noise contamination. In the second part, the vibration control
effectiveness of passive tuned mass dampers (PTMDs) to reduce
the seismic responses of torsionally-coupled buildings is
investigated. Some practical design issues such as the optimal
installed location of PTMDs are considered in this study. The
optimal PTMD''s system parameters are determined by minimizing
the mean-square displacement response ratio of controlled DOF
between the building with and without PTMDs. In addition, the
parametric studies about the PTMD''s planar position and effect
of detuning are investigated to realize their influence on the
response control efficacy. Finally, numerical results from
several typical multi-story torsionally-coupled buildings under
bi-directional components of 1940 and 1979 El Centro earthquakes
verify that the proposed optimal PTMDs are able to effectively
reduce the building responses.
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