The traditional base-isolated system is vulnerable to long-period ground motions, which usually result in a large displacement concentration at the isolated floor due to the resonant effect. To address this issue, two types of base isolation systems with tuned inerter dampers (TID) composed of a spring, an inerter and a dashpot in serial or parallel, are proposed and evaluated in this paper. The design parameters of the two TID isolation systems are optimized using the H2 norm criteria to achieve the best RMS vibration performance under stochastic excitation. The TID frequency ratio and damping ratio are defined as the design parameters, whose optimal values are analytically derived for the undamped primary system and numerically verified. The results show that the optimum exists for isolation system with serial TID (inerter and dashpot in serious), while in the parallel TID isolation system large TID stiffness and large TID damping are preferred in practice. The parallel TID system cannot be tuned optimally for practical structures, nevertheless, it still achieves a better isolation performance than the optimal serial system by an appropriate selection of the design parameters. The influence of the structural parameters on the optimal design parameters are studied. Case studies are conducted in comparison with the traditional isolation system for a laboratory prototype of a five-story building. The proposed optimal serial TID isolation system has 59% more reduction in the RMS relative displacement between the superstructure and base and 58% in the RMS response of the base vibration under the far-fault earthquake. And 52% and 56% more reductions in the RMS relative displacement and the base vibration are respectively achieved under the near-fault earthquake. The potential power in the TID isolations in earthquakes are also examined.
this paper, a novel semi-active magnetorheological tuned liquid column damper (MR-TLCD) device combining tuned liquid column damper (TLCD) and magnetorheological damper (MRD) is devised for wind or earthquake vibration control of civil structures. In this device, a traditional moving head loss in the TLCD is replaced with a controlled MRD in the bottom or one side of the vertical column, which can easily and rapidly adjust the damping of the device. A semi-active experimental prototype MR-TLCD consisting of a shear rotary MRD and a TLCD is built. Based on the four basic presumptions, a dynamic model of the devised MR-TLCD is established using the Lagrange equation. In this equation, the formula of MRD employs the Bingham Boltzmann model. The natural frequency of the MR-TLCD is determined by the total central length and spring stiffness. It is worth noting that the natural frequency differs with the simple TLCD, because the device adds a joint spring. An equivalent linear damping expression is developed under harmonic excitation, and its mechanical model is developed using the equivalent period displacement and the coulomb friction force of MRD. At the same time, the equivalent damping can be adjusted by the real-time applied current, which can achieve the semi-active control performance. To validate the proposed frequency and damping model, Experimental test is conducted on a section area 150mm × 150mm and a total length 2.24m of the MR-TLCD dimensions. Comparisons are made between predicted and measured TLCD liquid surface displacement motion. The result shows the error of its nature frequency is only 2.29%.
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