Tsubasa SATO

Study on vibration characteristics of wooden structures based on observation results

Takaaki IKEDA

In June 2019，an earthquake with a seismic intensity of over 6 occurred off the coast of Yamagata Prefecture. By this earthquake，A seismic intensity of over 6 was observed at Fuya， Murakami city，but the wooden structure didn’t collapse．Therefore，in this study，I calculated the natural frequency of the wooden structure in Fuya and investigated the possibility that the response of the wooden structure was amplified．
The natural frequency was calculated using the transfer function from the waveform obtained by microtremor observation．In addition，We measured the microtremor of two wooden houses in Nakahama．
As a result of calculating the natural frequency，For wooden house A，ridge direction is 3.8Hz and span direction is 4.0Hz，For wooden house B，ridge direction is 5.7Hz and span direction is 5.0Hz．
From this result，the natural frequency of ridge direction was smaller than the natural frequency of span direction in the house A．The reason why the natural frequency was reversed was considered to be the influence of Niigata earthquake．Niigata earthquake caused cracks in the ridge direction．It was considered that the natural frequency was reversed due to this crack in the ridge direction．
Finally，the obtained natural frequency was evaluated．Therefore，I made the acceleration response spectrum of the earthquake off Yamagata Prefecture．Then，both the wooden house A and the wooden house B deviated from the frequency at which the acceleration response peaked．However，when compared with the acceleration response spectrum of 1995 South Hyogo Prefecture Earthquake，the maximum acceleration response of the earthquake off the coast of Yamagata Prefecture was larger．Therefore，it is necessary to investigate from the point of view of seismic strength of wooden structures in the future．