S U M M A R YWe developed a new method of geodetic data inversion to estimate slip history at a plate interface by using Akaike's Bayesian Information Criterion (ABIC). In this method we considered the effects of viscoelastic stress relaxation in the asthenosphere, which cannot be neglected to estimate slip history at a plate interface during one earthquake cycle. We also introduced a proper formulation to incorporate two sorts of partially dependent prior information into observed data by Bayes' rule. By applying the new inversion method to levelling data for 1893-1983 in Shikoku, southwestern Japan, we reconstructed the pattern of space-time variation in slip motion during one earthquake cycle, including the 1946 Nankai earthquake, at the interface between the Eurasian and the Philippine Sea plates. The result shows that a steady slip motion at a plate convergence rate (40 mm yr −1 ) proceeds in the shallow and the deep regions through the entire earthquake cycle. In the intermediate depth range (10-30 km), on the other hand, an instantaneous slip of approximately 4 m occurs at the time of the Nankai earthquake. After that, this portion keeps in stationary contact until the occurrence of the next Nankai earthquake. If we neglect the effects of viscoelastic stress relaxation, the inversion analysis gives geophysically unrealistic results.
Base-isolated structures are vulnerable to long-period ground motions due to resonances. The hybrid control strategy combining traditional tuned mass dampers (TMDs) with base-isolation systems has been proved by some researchers to be effective in preventing the resonant behaviors. However, large space for TMDs is required because of large stroke lengths of TMDs, which may be difficult to realize in practical applications. In this paper, a non-traditional TMD that is directly connected to the ground by a dashpot is adopted to mitigate the resonant behavior of a structure. It is found that the conventional design method of traditional TMDs based on the quasifixed points theory cannot provide the global minimum value of the objective function for non-traditional TMD systems. An optimum design method for obtaining a wide suppression bandwidth is proposed. Seismic-induced vibration control for a three degree-of-freedom base-isolated structural system with a non-traditional TMD is studied. The control effect of the optimally designed non-traditional TMD is significantly improved, and the stroke length of the non-traditional TMD is greatly reduced, compared with the traditional TMD during near-field long-period earthquakes. In these regards, non-traditional TMDs may provide a better solution for retrofitting or constructing base-isolated structures. = 0.119): (a) absolute acceleration of primary structure; (b) stroke length of tuned mass damper (TMD). OPTIMUM DESIGN FOR MORE EFFECTIVE TMD
SUMMARY Floor isolation system (FIS) achieving very small floor accelerations has been used to ensure human comfortability or protect important equipments in buildings. Tuned mass damper (TMD) with large mass ratios has been demonstrated to be robust with respect to the changes in structural properties. This paper presents the concept of a TMD floor vibration control system, which takes advantages of both the FIS and TMD. Such a system is called ‘TMD floor system’ herein. The TMD floor system (TMDFS) in which building floors serve as TMDs can achieve large mass ratio without additional masses. Furthermore, multiple TMD floors installed in a building can control multimode vibrations. Then, an optimal design process, where the objective function is set as the maximum magnitude of the frequency response functions of inter‐storey drifts, is proposed to determine the TMD floor parameters. Additionally, the multimode approach is applied to determine the optimal locations of TMD floors if not all of the floors in a building can serve as TMDs. In addition to the numerical simulations, a scaled model shaking table experiment is also conducted. Both the numerical and experimental results show that the absolute accelerations of the TMD floors are smaller than those of the main structural storeys, which indicates the TMDFS maintains the merit of FIS while greatly reducing seismic responses of main structures. Copyright © 2013 John Wiley & Sons, Ltd.
SUMMARYA variant type of tuned mass damper (TMD) termed as 'non-traditional TMD (NTTMD)' is recently proposed. Mainly focusing on the employment of TMD for seismic response control, especially for base-isolated or high-rise structures, this paper aims to derive design formulae of NTTMDs based on two methodologies with different targets. One is the fixed points theory with the performance index set as the maximum magnitude of the frequency response function of the relative displacement of the primary structure with respect to the ground acceleration, and the other is the stability maximization criterion (SMC) to make the free vibration of the primary structure decay in the minimum duration. Such optimally designed NTTMDs are compared with traditional TMDs by conducting both numerical simulations and experiments. The optimum-designed NTTMDs are demonstrated to be more effective than the optimum-designed traditional TMDs, with smaller stroke length required. In particular, the effectiveness of the TMDs combined with a base-isolated structure is investigated by small-scale model experimental tests subjected to a time scaled long period impulsive excitation, and it is demonstrated that the SMC-based NTTMD can suppress structural free vibration responses in the minimum duration and requires much smaller accommodation space. Additionally, a small-scale shaking table experiment on a high-rise bending model attached with a SMC-based NTTMD is conducted. This study indicates that NTTMD has a high potential to apply to seismic response control or retrofit of structures such as base-isolated or central column-integrated high-rise structures even if only a limited space is available for accommodating TMDs.
SUMMARYPerhaps one of the most signiÿcant technological innovations in the structural engineering ÿeld is the practical application of active and semiactive control to civil structures. A number of structures integrating active, hybrid, and semiactive response control technologies have been constructed in Japan. Most of them are building structures. This paper provides an overview of those building structures, focusing mainly on the types of buildings that are controlled, and on the types of control devices that are implemented. Future directions of structural engineering are also discussed.
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