In the event of an earthquake that could cause damage to the house, various institutions are conducting survey, such as emergency risk determination, on the damage level of houses for different purposes. Though both of these investigations differ in purpose and criteria, they are indispensable for restoration and reconstruction of housing and residents' lives, and accurate and stable survey results are required. However, in the survey based on visual, it is impossible to avoid variations and bias of judgment by the implementer. In addition, when many houses suffer damage, it is essential to shorten the investigation time in order to respond promptly.
Meanwhile, due to technological innovation in recent years, an acceleration sensor that can be applied to microtremor measurement has been developed. Main improvements are improvement of accuracy in the low frequency range due to high resolution and noise reduction, less burdensome transportation by weight reduction and ultra miniaturization, simplification of installation and measurement wirelessly, and cost reduction of the measurement system.
In the review of these background, in this paper, for the purpose of disaster evaluation of low-rise housing by microtremor measurement directed to Japanese conventional wooden and light-gauge steel structure, the reduction rate of the primary natural frequency of the vibration table test fm / f0 (However, f0: initial primary natural frequency, fm: the primary natural frequency after excitation (earthquake)) was newly constructed. And by comparing and examining past evaluation formulas related to traditional wooden structure, the following knowledge was obtained.
· Regarding each shaking table test of conventional wooden, light-gauge steel, and traditional wooden structure considered in this paper, regardless of the structure type, it is possible to unify the deformation dependence evaluation formula of the primary natural frequency decrease rate using a coefficient γ0.5m, which is γmax when (fm/f0)2 is 0.5.
· The coefficient α, relating to the decrease gradient to the maximum deformation angle of the reduction rate of the primary natural frequency, make it possible to improve the accuracy of the evaluation formula of the primary natural frequency decrease rate, between a micro deformation and the deformation angle 1/50rad, which is the criteria to determine the continued availability of houses.
However, the findings obtained here are based on specific experimental results, and from now on, it is necessary to verify the validity of the evaluation formula with reference to the results of the actual shaking table experiment.
