| Summary: | 碩士 === 朝陽科技大學 === 營建工程系碩士班 === 99 === Located at the active western circum-Pacific seismic belt where the Luzon arc of the Philippine Sea plate and the Eurasian plate collides with each other, Taiwan is subject to frequent earthquakes. Because of their devastating potential, there is a growing research interest in areas of earthquake engineering and seismic hazard mitigation. Although a great deal is known about where earthquakes are likely to occur, there is currently no reliable way to predict the time when an event will occur in any specific location. In this regard, seismic fragilities play an important role in performance-based design engineering and seismic risk analysis in region of high seismic activities as in Taiwan.
In this study, the capacity spectrum method (CSM) employed in ATC-40 is adopted here to evaluate the seismic capacity of pile-supported wharves. Utilizing the SAP 2000 analysis program, the capacity curve of the target structure can be obtained by implementing the push over analysis for the wharf structures. The response spectra can then be scaled by considering the PGA values associated with the design earthquake and maximum possible earthquake. The performance points under earthquake intensity of the above two levels can be yielded by using the intersection point of capacity spectrum and demand spectrum considering nonlinear response effect. The states of these performance points can then be used to assess the seismic capacity of structure.
An approach to estimate seismic fragility without the need to perform the nonlinear dynamic analysis for determining the damage state of the structure as well as the need to perform the Monte Carlo simulation for calculating the damage probability with respect to ground motion of different intensities is developed here. The capacity spectrum method employed is again adopted to determine the damage state of the target wharf structure. Consequently, nonlinear push over analysis is performed to obtain the capacity curve of the target structure and the damage state of the structure can then be determined by using the intersection points of capacity spectrum and demand spectrum associated with ground motion within certain range of PGA values. Fragility curves in this study are assumed to be lognormal distribution described by two parameters and are developed as a function of peak ground acceleration (PGA). The estimation of these two parameters is done by the maximum likelihood method treating each event of damage as a realization from a Bernoulli experiment. In fact, genetic algorithm(GA) is employed to obtain the parameters. The uncertainty associated with the ground motion is simulated by analyzing the statistical characteristics of the records of ground motion collected near the site. In addition, the uncertainties associated with the capacity spectrum and the thresholds of different damage states are also analyzed. Finally, fragility curves considering different level of uncertainties are constructed and compared for target pile-supported wharves.
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