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In previous studies, it was suggested that integrating the vertical component of strong acceleration records in time domain often yields a residual velocity, which is always negative. This study proposes a generation mechanism of this residual velocity V_non; at the moment of the action of a horizontal inertia force, the sensor is tentatively tilted in that direction and the horizontal inertia force multiplied by sinθ is felt by the vertical sensor, where θ is the tilt angle. The tilt of the sensor can be either due to the shear deformation of the ground or the tilt of the house. The apparent residual velocity generated by this mechanism is always negative. It was shown for the K-NET records for which the effect of the housing is small that the proposed mechanism can readily explain the order of magnitude of the observed V_non values.
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The types of embankment damage during earthquakes are crest or slope tension cracking and circular sliding. However, it remains unclear which damage occurs during which earthquake. In a previous study, we conducted a crack propagation analysis using Peridynamics (PD) to examine various embankment damage types. The results showed that the type of damage varies with the maximum acceleration and frequency. However, the analysis was limited to two dimensions. Therefore, in this study, a three-dimensional seismic response PD was developed and compared with the two-dimensional PD to demonstrate the validity of the code. We also investigated the influence of the maximum acceleration and frequency on the failure modes.
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To facilitate effective and efficient earthquake disaster prevention, understanding the subsurface structure of an area with a high degree of accuracy is important. Generally, accurate subsurface structure estimation requires high-density borehole data; however, the low density of boring data in regional cities makes it difficult to construct a highly accurate subsurface structure model. Recently, technological progress has been made in estimating the subsurface structure using microtremors observations. Thus, in this study, we attempted to estimate the three-dimensional subsurface structure with high accuracy by combining borehole and microtremor observation data. The validity of the estimated subsurface structure was validated in terms of topography and amplification characteristics.
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In this paper, we examine the dynamic properties of an existing 3‐story light‐gauge steel‐framed house based on the observation records obtained from seismic observations and microtremor measurement. As a result, it was concluded as follows. The first is that a decrease in the natural frequency and an increase in the damping constant, which are thought to be caused by earthquakes and aging, were observed. The second is that even within an earthquake, the natural frequency drops during periods of particularly large amplitude and then recovers. It is possible that this characteristic mainly depends on a reversible phenomenon such as friction between non-structural members. The third is that at the microtremor level, the natural frequency is higher and the damping constant is smaller than during the earthquake.
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In this study, five types of optical fiber cables were buried at a test site to carry out Distributed Acoustic Sensing (DAS) measurements. Three types of interrogators were independently tested with these buried cables, while multiple geophones were deployed at equal intervals for comparative analysis. Strain rate records, calculated by dividing the difference between adjacent geophones by the installation interval, confirmed that records of hammer-induced excitations were successfully obtained. Moreover, microtremor observation records were effective in estimating the phase velocity in the frequency band of approximately 2 Hz or higher. Seismic interferometry analysis of the DAS records and combination of DAS and microtremor records revealed that the dispersion curves are consistent with the Rayleigh wave phase velocity estimated by the microtremor survey.
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First, we present a method for obtaining the eigenvalues and eigenvectors of a multi-degree-of-freedom system with nonproportional complex damping. These eigenvalues and eigenvectors are complex and appear in conjugate pairs, corresponding to the number of masses, with forward waves and their conjugate backward waves. By leveraging the orthogonality of the eigenvectors, we show that the seismic transfer function for each mass can be expressed as a superposition of the transfer functions of the complex modes of the forward wave, exhibiting conjugate symmetry. Similarly, using the orthogonality of the real eigenvectors, we derive an approximate transfer function by superimposing the transfer functions of the real modes. Finally, numerical calculations using a simple model are performed to validate the proposed complex eigenvalue analysis method and the transfer function based on complex modes. Additionally, we discuss the reliability of the transfer function derived from real modes.
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We propose a method to evaluate the restorability of railway structures. In the proposed method, all earthquake motions expected within a structure’s design service life are used as the design earthquake motions. In addition, the recovery time after an earthquake, which is directly related to early recovery, is used as the verification index. We also propose a more practical method of representing structural conditions that correspond to the same recovery time using a nomogram by performing calculations under various conditions in advance. The proposed method allows us to design structures that can be restored more easily, following the same procedure as conventional seismic design, and it is expected to shorten the recovery time after an earthquake.
