This paper presents the identification and assessment of the dynamic characteristics of building and bridge structures from the long-term monitoring of seismic response data. Over 40 events of the seismic response data of these structures during the past 10 years were used. To extract the dynamic characteristics of the structures from its seismic response data, the time-domain data-driven subspace identification (SI-DATA) technique is used to extract the system natural frequencies, damping ratios and mode shapes. To enhance the stability of the identified real system poles in using SI-DATA, an algorithm of removing spurious modes is used. Discussion on the identified system dynamic characteristics of the structures under different intensity level of ground excitation is presented. Effect of soil-structural interaction on the identified system natural frequencies and damping ratios by considering either free-field data or basement data as input in subspace identification is also discussed.
SUMMARYSeismic isolation devices and technology have been developed in the last two decades and the ÿrst seismic-isolated bridge, Bai-Ho Bridge, in Taiwan was completed in 1999. This bridge was equipped with a seismic monitoring system under the Taiwan Strong Motion Instrumentation Program (TSMIP). On 22 October 1999, a moderate earthquake took place and struck the bridge. The seismic monitoring sensors were normally triggered and produced an intact time history for the health monitoring of the bridge system. The data set provided valuable records about the seismic response of the isolation bridge structure. This paper uses this data to explore the vibration mechanism of Bai-Ho Bridge. The analysis includes (1) the global dynamic behavior identiÿcation and (2) the local component mechanism of the bridge such as the LRB and boundary condition between the deck and the abutments. Both the EMD + HHT method and the non-linear parametric model were used to identify the model of the bridge structure.
Taiwan is located on the boundary between the Eurasia Plate and Philippine Sea Plate, which is a very high seismicity rate area. We begin calculating the earthquake occurrence probability using four recurrence models to mitigate seismic disasters. We focus on estimating the occurrence probabilities for regional earthquake sources based on the catalog released by the Central Weather Bureau over the period from 1900 to 2011. According to the tectonic and seismicity characteristics areas in and around Taiwan are divided into several zones for shallow and deep earthquakes. We utilize four recurrence models to estimate the earthquake occurrence probabilities over the next 30 and 50 years, respectively. In addition, the grid-based probabilities in 0.1° × 0.1° spatial size are calculated using the micro-zoning method. The results obtained from four recurrence models show that areas with high values over the next 30 and 50 years are correlated with two subduction zones and a suture zone. High probabilities in the western foothills appear highly active tectonic. Moreover, the high values appear at in Eastern Taiwan, offshore Hualien County. There are discrepancies between the results from the four models. The highest grid-based probability is about 3.0, 3.5, 2.5 and 3.5% for the Lognormal, Gamma, Exponential, and Weibull models, respectively. The inland probabilities are below 0.5% for the results from Lognormal, Gamma, and Weibull models. Even so, the results from the Exponential model are upmost in the range from 0.5 -1.0%.
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