Jun Tobita

Evaluation of nonstationary damping characteristics of structures under earthquake excitations

Abstract The time-varying vibration characteristics of structures are investigated by applying system identification techniques to a series of short-time segments of the observed earthquake records. Structures are modelled as parametric, linear, time-invariant systems in each time segment, and the identification is performed in the frequency domain. To show the effectiveness of such an equivalent linear, time-variant model in evaluating the nonstationary and nonlinear vibration systems, simulated hysteretic responses are examined by the procedure. Examples of actual buildings are given in which distinctive amplitude-dependent damping characteristics of base-isolated structures, and nonlinear properties with stiffness degradation of a 9-story SRC building during strong excitations are evaluated.

620 Maybe the World's First Attempt on Vibration Engineering Lecture : Report of Experience-Based Program : Building to Perform a Lecture Vibrated Freely

Susumu HARA, Nobuo FUKUWA, Toshihiro NODA, Takashi TASHIRO, Jun TOBITA, Takuya NAGAE, Kazumi KURATA and Tsuyoshi INOUE Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan

Ground Vibration Caused by Tunnel Construction and its Effect on an Electron Microscope

Abstract In this study, we observed the vibrations caused by the construction of a roadway tunnel excavated using the New Austrian Tunneling Method (NATM) in an urban area. We analyzed the resulting vibrations and disturbances and their effect on a high-voltage electron microscope (HVEM). The characteristics of the construction equipment, various construction tasks, wave propagation and attenuation in the soil, along with the transmission of vibration forces to adjacent buildings were also clarified. These findings were combined and the effects on the HVEM were examined to model vibration-induced disturbances. The accuracy of these findings was confirmed by comparing the results obtained with actual observations that were recorded later. The findings of this study are expected to enhance the ability to distinguish between the many factors involved in vibration-induced disturbances caused by equipment. The findings could also be applied to monitoring construction activities and predicting the effects of vibration-induced disturbances on high-precision equipment.