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Seismic records collected from earthquake with large magnitude and far distance may contain long period seismic waves which have small amplitude but with dominant period up to 10 sec. For a general situation, the long period seismic waves will not endanger the safety of the structural system or cause any uncomfortable for human activity. On the con...
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Context 1
... that Japan earthquake, there were also several far distant earthquakes that brought the unexpected shutdown to wafer scanners in many high-tech fabs in the Science Parks situated in Taiwan. Table 1 lists the earthquake information and the impact of these earthquakes. It is important to point out that not all the far distant earthquakes can cause vibration-sensitive equipments to shutdown, therefore, some ground motion features need to be extracted and identified from the recorded seismic waveforms. ...
Context 2
... the results demonstrate that the severer impact occurred on the wafer scanners, the higher portion of low frequent content is dominated. On the other hand, it was observed that the slope index increased with respect to time for 4 seismic events (April 11, 2012, April 20, 2013, April 25, 2015, and May 30, 2015 Table 1. Therefore, the brief examination reveals that he proposed features can be used to detect the far distant earthquake that is potential damaging and provide early warning for it. ...
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Ground motions induced by strong, distant earthquakes may contain extremely long-period seismic waves that have a dominant period of up to 10 s. In general, these long-period seismic waves have small amplitudes and do not endanger the safety of building structures and civil infrastructures. However, they may bring unexpected shutdown of some vibrat...
Citations
This study conducted the parametric and quantitative analysis of the influence of soil-structure cluster interaction (SSCI) on ground motion. Based on the results of the shaking table test and numerical simulation, the changes in the characteristics of ground motion with the alterations of multiple factors are explored via wavelet packet decomposition. The results indicated that: (a) structure cluster reduces the site eigenfrequency, thereby amplifying the low-frequency components of ground motion and attenuating the high-frequency components. Ground can capture more of the high-frequency seismic energy coming from the bedrock through the long piles; (b) homogeneous structures inhibit the ground motion component with a frequency close to the structural eigenfrequency. The effect is more significant with increasing the number of structures and is gradually transformed into the energy dissipation effect acted in the wideband with increasing the damping ratio of structures; (c) the peak ground acceleration gradually diminishes from the center of the homogeneous structure cluster outward and this spatial variation is more pronounced under the excitation with high-frequency seismic waves. Furthermore, the energy variation index and coefficient of variation are employed to quantify the influence of SSCI on ground motion. The mass density of the structure cluster is the crucial variable for affecting the holistic variation of free-field ground motion. The spatial variation of ground motion attenuates significantly with increasing the thickness, shear wave velocity of subsoil, structural spacing, and homogeneity of structure cluster. The spacing between the structures required for the degeneration of SSCI into soil-structure interaction is chiefly related to the site condition and the structural frequency, which is enlarged with the decrease in soil shear wave velocity and structural frequency.
Nonstructural damage brings serious threats to life safety, property loss, and functional loss and results in countless economic losses, directly and indirectly. Recently, researchers have found that overall seismic hazard can only be reduced once the nonstructural components (secondary structures) receives the same degree of consideration as primary structures. To be functional during and after an earthquake, a passive control device in the form of isolation system has been acknowledged as an effective method for the nonstructural components, especially the critical equipment. However, the equipment with isolation system may still suffer from low-frequency resonances; for example, the vibration sensitive equipment may have excessive isolator displacements when subjected to a near-fault earthquake, and moreover, the ultra-sensitive equipment may have glitch and breakdown when subjected to a long-period ground motion generated by a far distant earthquake. Clearly, the seismic mitigation of vibration-sensitive equipment is one part of a comprehensive measure against earthquakes and shall be developed.
To achieve this, the isolation systems with adequate periods are still necessary. First, the smart and adaptable active or semi-active control systems are integrated with the equipment isolation systems. Considering the non-stationary nature of earthquake excitations, signal processing techniques are utilized to enhance the traditional control algorithms. This advanced control algorithm can control both structures and nonstructural components (vibration-sensitive equipment) simultaneously to overcome the limitations of traditional control algorithms under seismic excitations. Moreover, the active or semi-active isolation system combined with various control algorithms against near-fault earthquakes is investigated through both numerical simulation and experimental validation. Nevertheless, some equipment is too sensitive to survive any seismic ground motion, even the small one generated by a far distant earthquake. For this kind of ultra-sensitive equipment, an alternative measure is to turn off the equipment before seismic vibration by applying feature extraction techniques to the ground motion data collected from strong motion networks in Taiwan. The ground motion features efficiently extracted from the seismic waveforms and the dynamic characteristics numerically simulated according to the ultra-sensitive equipment are then correlated to investigate the possibility of issuing a timely warning, turning off the equipment, and avoiding the impact before the arrival of the main shock. Finally, by providing the advanced control algorithm and the informative early warning, the seismic vibration of vibration-sensitive equipment can be mitigated, the functionality of critical equipment can be secured, and the overall seismic hazard can be consequently reduced.
