Evaluation of Existing Building Dynamic Characteristics Based on Micro-Tremor Measurements and Strong Motion Observations

Abstract eng:
In Japan, huge earthquakes such as the Tokyo inland earthquake and the Tokai-Tonankai-Nankai earthquake are predicted to occur in the near future. For earthquake-induced damage estimation and seismic performance evaluation of buildings, it is important to understand the dynamic characteristics of buildings. A large number of studies have employed practical observations to investigate the dynamic characteristics of super high-rise buildings and quake-absorbing structures; however, there is currently a lack of studies focusing on low- and medium-rise buildings. To address the lack of research on such structures, the authors installed seismometers in an existing steel-frame reinforced concrete (SRC) building in Tokyo, and conducted long-term-observations. After several years, during which time the 2011 Off the Pacific Coast of Tohoku Earthquake occurred, the dynamic characteristics of this building based on the observation records were investigated. Micro-tremor measurements of this building were also acquired on several occasions, and the dynamic characteristics from these measurements were investigated. Additionally, vibration analysis of a three-dimensional frame model was performed, and the differences between the observations and the analysis were investigated. The building adopted in this study was a nine-story SRC residential building located on the alluvium ground in Tokyo and built in September 1978. Micro-tremor measurements were acquired in September 2007, and strong motion observations were continuously taken beginning in May 2008. The building experienced the 2011 Off the Pacific Coast of Tohoku Earthquake in March 2011, and micro-tremor measurements were acquired again in October 2012 and October 2013. The strong motion observations were recorded using a small-sized strong-motion-seismograph with semiconductor sensors at a sampling rate of 100 Hz. The measurement points were located at the first floor and the roof floor of the building in order to record the acceleration in three dimensions on each floor. The micro-tremor measurements were recorded using servo-type speedometers at a sampling rate of 200 Hz. The analysis model consisted of line elements comprising the three-dimensional frame. Eigenvalue analysis was performed using a three-dimensional structural analysis software, and the vibration mode and natural frequency of the frame model were calculated. As for the strong motion observations, 36 records excluding incomplete or incorrect data were obtained. The changes in the dynamic characteristics of the building during the course of the long-term observations were investigated through analysis of the strong motion data. The natural period of the building was found to be substantially longer during the 3.11 earthquake, and gradually reduced over time following the event. The comparison between the analyses of the micro-tremor measurements and the frame model analysis revealed nearly identical results for the vibration mode and natural frequency.

• Export as: BibTeX | MARC | MARCXML | DC | EndNote | NLM | RefWorks
• Add to your basket