NUMERICAL MODELLING OF MULTIPLE TUNED MASS DAMPER EQUIPPED WITH MAGNETO RHEOLOGICAL DAMPER FOR ATTENUATION OF BUILDING SEISMIC RESPONSES

Abstract

The Tuned Mass Damper (TMD) is generally as a passive vibration control device consisting of added auxiliary mass with functioning spring and damping elements. TMD is basically designed to be tuned to the dominant frequency of a structure which the excitation of frequency will resonate the structural motion out of phase to reduce unwanted vibration. However, a single unit TMD is only capable of suppressing the fundamental structural mode. In order to control multimode vibrations and to cater wide band seismic frequency, more than one TMD is required to improve the effectiveness of a control mechanism. For the purpose of this study, a 3-storey benchmark reinforced structural building subjected to El Centro seismic ground motion is modelled as uncontrolled Primary Structure (PS) by considering appropriate structural properties such as stiffness and damping. Mathematical modelling of uncontrolled PS is developed and further evaluated numerically by assuming the PS as an equivalent lumped system. For the case of controlled PS which the passive mechanism is included to the system, optimum parameters of both TMD and Multiple TMD (MTMD) are designed to be tuned to the dedicated structural modes where the performance is dependent on specified parameters such as auxiliary mass ratio, optimum damping ratio, and optimum frequency ratio. The eigen value analysis is carried out by assuming that the structure is a linear time-invariant system. The input and output components of structural system arrangements are then characterized in the transfer function manner and then converted into state space function. To enhance structural control effectiveness, the adaptive system is incorporated by the attachment of Magneto-Rheological (MR) damper to both single TMD and MTMD passive system. The response analysis of the control system arrangements is executed using both time history and frequency response analysis. The main objectives of the design are to minimize both structural peak and Root Mean Square (RMS) displacements. From the analysis, the designed control mechanisms are concluded as highly effective in reducing all structural floor displacements for the semi-active cases with 99% displacement reduction for the third and second floors, and 98% for the first floor, compared to the uncontrolled case. It is concluded that the MR damper significantly contributed to the enhancement of the passive system to mitigate structural seismic vibration.