The combined anti-vibration platform, which was composed of the mega-frame platform (MFP) and the multiple extended tuned mass damper (METMD) system, was simplified as a multiple-degree-of-freedom system for the study of the resonant responses’ decrease of the platforms under the rare seismic wave forces. The METMD system was made up of several ETMD units that had a specific frequencies’ bandwidth. The average frequency was tuned to the platform’s first natural frequency, which was the target frequency to be controlled. So, the offshore platform and the METMD system were simplified to an m+1 DOFs system to be analyzed theoretically. The ratio of the METMD system mass to the platform residual mass was 14% and the ratio of the exciting frequency to the platform’s natural frequency varied between 0.5 and 1.5 The theoretical analysis shows that the platform has the best vibration control effect when the frequencies’ bandwidth is 0.45; the damping coefficient is 0.1 and the number of the ETMDs is 5. In order to analyze the dynamic response of the combined anti-vibration platform under the random seismic loads, the El-Centro, Taft and Qian’an seismic waves were chosen as typical loads and their maximal acceleration values had been adjusted according to 8 level fortification under rarely occurred earthquake. The FEM simulations shows that: 1) the average vibration displacements decrease ratios of the entire platform in the X, Y, Z directions are 80.48%, 61.93% and 64.31% respectively under the El-Centro seismic wave; 2) the X, Y, Z directions average decrease ratios for the entire platform are 84.21%, 49.95% and 56.6% respectively under the Taft seismic wave; 3) the X, Y, Z directions average decrease ratios of the entire platform are 50.09%, 32.645% and 23.34% respectively under the Qian’an seismic wave; and 4) the average displacement decrease ratios of the whole platform in X, Y and Z-direction are 71.59%, 48.18% and 48.08% respectively considering all seismic waves above. So the combined anti-vibration platform has the better ability on the vibration control under the random seismic loads.

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