CLARIFICATION OF THE AMPLITUDE DEPENDENCY OF NATURAL FREQUENCIES OF TRADITIONAL TIMBER FRAME STRUCTURES FOR UTILIZATION OF AMBIENT VIBRATION MEASUREMENTS

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  • 常時微動計測の活用に向けた伝統木造軸組架構の固有振動数の変形角依存性の解明

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Abstract

<p>We aim to apply the natural frequencies obtained from ambient vibration measurements to the following three points for traditional wooden buildings: simple seismic diagnoses, rapid assessment of the degree of damage, and verification of the analytical models of buildings. However, there are some problems in achieving each of them as follows: </p><p>1) A simple seismic diagnosis is to estimate the maximum response of a building to a postulated earthquake ground motion from the amplitude dependency of the natural frequency using the response spectrum method. If the amplitude dependency of natural frequency can be estimated using the natural frequency obtained from ambient vibration measurement, the maximum response of the building can be easily predicted. However, we had not obtained the amplitude dependency of natural frequency from the extremely minute deformation region related to the ambient vibration to the large deformation region related to the collapse, which is necessary for this purpose. </p><p>2) In the rapid assessment of the degree of damage, we focus on the fact that the natural frequency of a building, which is obtained by ambient vibration measurement, decreases after an earthquake occurs. The maximum deformation angle during an earthquake can be estimated from the rate of decrease in the natural frequency of the building, which is obtained from ambient vibration measurement. However, there were insufficient data on the rate of decrease. </p><p>3) The validity of the analytical model is verified by comparing the fundamental natural frequency that corresponds to the initial stiffness of the solid analytical model, which is usually prepared in detailed seismic diagnosis, with that obtained from ambient vibration measurement. In general, the natural frequencies of models are lower than those obtained from ambient vibration measurement, but the quantitative relationship has not been fully understood. </p><p>Based on the above background, in this study, we gained quantitative data that is essential for realizing the above purposes on five kinds of test specimens with different building components. The test specimens consisted of a common planar framework and various building components, such as dry mud wall panels and plasterboards. Two wooden frames were made for each type of test specimen, and these were connected by orthogonal beams so that they could stand on their own. </p><p>Three relationships were quantitatively clarified by combining ambient vibration measurements, vibration tests, and static loading tests: the amplitude dependency of the equivalent natural frequency, the maximum deformation angle dependency of the natural frequency in ambient vibration, and the relationship between the natural frequency that corresponds to the initial stiffness of analytical model and the natural frequency obtained from ambient vibration measurement. These results are essential to realizing the application methods: simple seismic diagnosis, rapid assessment of the degree of damage, and validation of the analytical model of the building, respectively. In addition, we proposed models based on previous studies for each relationship, which is useful to realize each of the application methods. </p>

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