EFFICACY OF TUNED MASS DAMPER FOR SEISMIC RESPONSE REDUCTION ON STEEL BRIDGES

Abstract

Use of energy damping systems is often questioned in earthquake resistant design of structures. Its applications are still limited as it has not attained full-recognition. One such system is tuned mass damper system which has proved its efficiency against wind forces. But its efficacy against seismic forces is yet to be justified. Present study is to check the efficacy of tuned mass damper system under seismic forces for steel truss bridges. Efficiency is checked for vertical displacement of mid-span of bridge under vertical ground motions. Steel truss bridges of different spans viz. 45.6 m, 61.0 m and 76.8 m are taken for study. Different time-history records of Uttarakhand region are taken for seismic analysis. An average response spectrum is developed using response spectrum of these time-histories. Again, spectrum based time-histories are generated using this response spectrum. Initially single tuned mass damper system is used to evaluate the effect of its different parameters on vertical displacement of bridge. Thereafter, average response reduction is calculated for all time-histories. Further, 3 TMD systems with different frequency attributes are used for response reduction. Change in average response reduction is observed with shift infrequency band as well as change in frequency band-width of 3 TMD system. Further, 5 TMD system is used, for all bridge models, with different frequency range as well as minor change in one frequency of TMD. Substantial reduction in response is observed when frequencies of TMD system is tuned with the excitation frequencies