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Liu J.Y.,National Taiwan University of Science and Technology | Chen C.H.,National Chung Cheng University | Sun Y.Y.,National Central University | Chen C.H.,National Cheng Kung University | And 7 more authors.
Geophysical Research Letters | Year: 2016

In this paper, concurrent/colocated measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency-continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011M9.0 Tohoku earthquake. No time delay between colocated infrasonic (i.e., super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves (i.e., STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan. © 2016. American Geophysical Union. All Rights Reserved.

Hsu T.-Y.,National Taipei University of Technology | Wu R.-T.,National Center for Research on Earthquake Engineering Taipei Taiwan | Chang K.-C.,National Center for Research on Earthquake Engineering Taipei Taiwan
Computer-Aided Civil and Infrastructure Engineering | Year: 2016

An on-site earthquake early warning system (EEWS) can provide more lead-time at regions that are close to the epicenter of an earthquake because only seismic information of a target site is required. Instead of leveraging the information of several stations, the on-site system extracts some P-wave features from the first few seconds of vertical ground acceleration of a single station. It then predicts the intensity of the forthcoming earthquake at the same station according to these features. However, the system may be triggered by some vibration signals that are not caused by an earthquake or by interference from electronic signals, which may consequently result in a false alarm at the station. Thus, this study proposes two approaches to distinguish the vibration signals caused by non-earthquake events from those caused by earthquake events based on support vector classification (SVC) and singular spectrum analysis (SSA). In the first approach (Approach I), the fast Fourier transform algorithm and the established SVC model are employed to classify the vibration signals. In the second approach (Approach II), a SSA criterion is added to Approach I for the purpose of identifying earthquake events that are classified as non-earthquake events by the SVC model with increased accuracy. Both approaches are verified by using data collected from the Taiwan Strong Motion Instrumentation Program and EEW stations of the National Center for Research on Earthquake Engineering. The results indicate that both of the proposed approaches effectively reduce the possibility of false alarms caused by an unknown vibration event. © 2016 Computer-Aided Civil and Infrastructure Engineering.

Lin P.-C.,National Center for Research on Earthquake Engineering Taipei Taiwan | Tsai K.-C.,National Taiwan University | Chang C.-A.,National Taiwan University | Hsiao Y.-Y.,National Taiwan University | Wu A.-C.,National Center for Research on Earthquake Engineering Taipei Taiwan
Earthquake Engineering and Structural Dynamics | Year: 2015

A thin-profile buckling-restrained brace (thin-BRB) consists of a rectangular steel casing and a flat steel core that is parallel to a gusset plate. A thin configuration reduces the width of the restraining member and thus saves usable space in buildings. However, deformable debonding layers, which cover the steel core plate in order to mitigate the difference between the peak tensile and compressive axial forces, provide a space for the steel core to form high mode buckling waves when the thin-BRB is under compression. The wave crests squeeze the debonding layers and produce outward forces on the inner surface of the restraining member. If the restraining member is too weak in sustaining the outward forces, local bulging failure occurs and the thin-BRB loses its compression capacity immediately. In order to investigate local bulging behavior, a total of 22 thin-BRB specimens with a ratio of steel core plate to restraining steel tube depth ranging from 0.3 to 0.7 and axial yield force capacities ranging from 421kN to 3036kN were tested by applying either cyclically increasing, decreasing, or constant axial strains. The restraining steel tube widths of all the specimens were smaller than 200mm and were infilled with mortar with a compressive >strength of 97MPa or 55MPa. Thirteen of the 22 thin-BRB specimens' restraining members bulged out when the compressive core strains exceeded 0.03. A seismic design method of the thin-BRB in preventing local bulging failure is proposed in this study. Test and finite element model (FEM) analysis results suggest that the outward forces can be estimated according to the BRB compressive strength, steel core high mode buckling wavelength, and the debonding layer thickness. In addition, the capacity of the restraining member in resisting the outward forces can be estimated by using the upper bound theory in plastic analysis. Both the FEM analysis and test results indicate that the proposed method is effective in predicting the possibility of local bulging failure. Test results indicate that the proposed design method is conservative for thin-BRB specimens with a large steel core plate to restraining steel tube depth ratio. This paper concludes with design recommendations for thin-BRBs for severe seismic services. © 2015 John Wiley & Sons, Ltd.

Chuang M.-C.,National Taiwan University | Tsai K.-C.,National Taiwan University | Lin P.-C.,National Center for Research on Earthquake Engineering Taipei Taiwan | Wu A.-C.,National Center for Research on Earthquake Engineering Taipei Taiwan
Earthquake Engineering and Structural Dynamics | Year: 2015

A welded end-slot buckling-restrained brace (WES-BRB) has been developed at the Taiwan National Center for Research on Earthquake Engineering (NCREE). A steel frame equipped with a WES-BRB can offer a cost-effective solution to meet interstory drift and earthquake-resistant design requirements for seismic steel buildings. According to the WES-BRB and connection design procedure proposed by NCREE, there are seven key elements of a buckling-restrained braced frame (BRBF) design that require design checking. In order to assist an engineer with the design of the WES-BRB members and connections, an innovative cloud service named Brace on Demand has been constructed at NCREE. In this study, using 581 BRBF design examples, the effectiveness of the proposed design procedures to meet all design checks is demonstrated. It is found that the most critical limit states for an initial design are joint region buckling, gusset plate buckling, and gusset-to-beam and gusset-to-column interface strength. Accordingly, the causes of improper designs and associated strategies for improving the initial designs are discussed in this paper. Recommendations on initial selections including the BRB joint size and gusset plate thickness are given. The paper provides the detailed road map for engineers to develop the spreadsheet for BRB and connection designs. © 2014 John Wiley & Sons, Ltd.

Chen P.-C.,National Center for Research on Earthquake Engineering Taipei Taiwan | Wang S.-J.,National Center for Research on Earthquake Engineering Taipei Taiwan
Structural Control and Health Monitoring | Year: 2016

Sloped rolling-type isolation devices incorporating built-in friction damping and pounding preventer have been verified to be effective for mitigation of seismic risks posed to critical equipment and facilities. Although the built-in damping design can effectively suppress excessive displacement responses, it also increases the acceleration transmitted to the protected object above the isolation device. In this study, a novel mechanism using embedded electromagnets is proposed to improve the control performance of the isolation device. By varying the input currents to the electromagnets, the corresponding magnetic force becomes controllable and can appropriately adjust the normal force applied to the sliding interface, leading to indirect semi-active control of friction damping force. The efficacy of the proposed mechanism is verified through several shaking table tests. Experimental results demonstrate that the control target of the isolation device can be semi-actively achieved using the electromagnetic mechanism. Accordingly, a numerical model of such a smart isolation system, the incorporation of the proposed controllable damping mechanism into the conventional sloped rolling-type isolation device, is proposed and calibrated by the experimental data. Its effectiveness and advantage can be clearly observed particularly when appropriate control algorithms are applied to calculating input currents for the electromagnets. © 2016 John Wiley & Sons, Ltd.

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