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A method is proposed to identify the story stiffness matrix of torsionally coupled shear buildings story by story, using the modal parameters extracted from Green’s functions. Numerical tests reveal that although the method is valid, robustness to noise is low. In particular, the stiffnesses of the top story are greatly underestimated due to non-cancellation of noise, indicating that noise-reduced modal parameters are of importance for identification. An application of the method to an existing building reveals that knowledge of the precise masses and moments of inertia of individual floors is required in advance, and that velocity recordings and their decomposition into three degrees of freedom using a precise location of the center of gravity may reduce noise of the modal parameters.
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The Fukui Earthquake wreaked havoc on the Kuzuryu River bank. In this study, we obtained microtremor observations on the Kuzuryu River bank. An extended spatial autocorrelation (eSPAC) analysis was applied to the collected array observation data to estimate the Rayleigh wave-phase velocity. The predominant period of the bank was calculated from single-point three-component observation. S-wave velocity structures were back-analyzed based on the H/V spectrum. It was confirmed that the earthquake damages on the bank were harmonized with the back-analyzed structures.
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This article derives a time-varying function of the momentary energy input to a linear elastic single-degree-of-freedom system with viscous and complex damping. The problem is formulated in the form of a Fourier series using the Fourier amplitude and the difference of Fourier phase angles. The numerical analysis results show that (1) the time-varying function formulated using the Fourier series corresponds to the envelope of ground acceleration, and (2) the maximum momentary input energy evaluated using the formulation in this paper agrees well with that obtained from time-history analysis.
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A phase transform angle is known to be an important parameter in the liquefaction analysis, but there is little research on the phase transform angle, it is assumed to be constant or to be proportional to the internal friction angle in practical. In this study, we read off phase transform angles and the internal friction angles from the cyclic shear test results on sand under the triaxial condition. It is found that the phase transform angles scatter between 18 and 28 degrees, and there is strong correlation with the internal friction angle when the fines content is less than 20 %. Based on the findings, an empirical equation is proposed in which the phase transform angle is expressed as a function with respect to the internal friction angle.
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This study investigated the frequent near-fault strong motions recorded during active series of inland crustal earthquakes using sorted and ranked pseudo-velocity response spectra and ranked response spectral ratios to realize performance-based design consideration for buildings. The impact of repeating strong motions on building responses could be determined by multiplying the response spectra of the design-standard earthquake motions or the target spectra by the proposed ranked response spectral ratios.
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In order to support disaster response activities, we developed an automatic damage classification model using aerial photographs obtained from several earthquakes in Japan. First, we visually classified all buildings into one of four damage levels, then constructed a training and test data set covering four damage levels. By using this training data set, we were able to develop a CNN-based damage detection model with higher performance than previous models. As a result, an average recall value of 70% was obtained, and we confirmed that it is sufficiently accurate to assess the state of disaster damage to wooden buildings in Japan.
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In this paper, we report the results of an analysis using microtremor array data to estimate a 1D S-wave velocity structure consisting of several layers and an S-wave 3 km/s layer around the Okinawa Islands. The depths of the top of S-wave 3 km/s layer at each site are 0.2 to 0.4 km in northern and western Okinawa Island and Kume Island, and 2.0 to 2.5 km in southern Okinawa Island. The average S-wave velocities of each layer (0.69, 1.10, 2.01, and 3.46 km/s) and the depth of the layer boundary are also presented for the four-layer model based on the estimation results for all locations.
