**Spring
2004
**

** ****Control of Seismic Vibration using TMD and Diagonal Bracing
**

Ferdaus Khan

In order to reduce the losses of life and property
due to excessive structural vibration under seismic motion, research workers
have been trying to define innovative approaches to improve performance of
engineered structures and infrastructure systems. The main
objective of the current work is to study the effectiveness of Tuned Mass Damper
(TMD) and Lateral Bracing System to control seismic vibration of RCC buildings.
For these purposes several two-dimensional RCC buildings of varying heights (2,
5, 10, 20 storied) are considered and results based on linear dynamic analyses
are studied. TMDs of optimized parameters are installed at the top of the
buildings while lateral diagonal bracings are provided at each story and
modifications of the structural behavior are studied for the El Centro
earthquake in USA (1940). Observations are made on the effect of mass ratio of
the so-called optimized TMD and stiffness of the diagonal bracing system on the
vibrations of the first and top floor of the structures as well as the critical
shear forces. The results are presented in terms of the statistics of structural
response, peak shear forces as well as the frequency spectra.
For the 2 and 5
storied buildings the standard deviations for both the first and top floor
relative deflections are reduced with the TMD mass ratio, but the reduction is
irregular for taller buildings, actually increasing with mass ratio for the
20-storied building. The results also show that for the 2, 5, 10 storied
building the maximum shear force is steadily reduced with different mass ratio
but in the 20 storied building shear force is increased with higher TMD mass
ratio. The TMDs reduce the spectral peak at the respective natural frequency of
the structure, which are predominantly maximum for the 2 and 5-storied
buildings. Similar analyses
have been done for all the buildings using diagonal bracings of different
stiffness. The Fourier amplitude spectra of first floor displacement show that
the bracings reduce the structural vibration mainly by increasing its natural
frequency This is particularly effective for the shorter and stiffer structures,
but not that successful for taller structures. |