Data Extraction of Structural Behaviors At the Moment of Earthquake Occurrence From Video Capturing Clips

Abstract eng:
When the Tohoku Taiheiyo-Oki Earthquake occurred at the east coast area of Tohoku region in Japan in 2011, lots of realtime video movies were recorded by mobile phone users and lots of video images of actual behaviors of buildings or infrastructures at just the moment of the natural disaster have been distributed through the web streaming site on the Internet. In this study, effective utilization of those video image resources for analyzing structural behaviors under the actual disasters is discussed. For this purpose, importance to provide data extracting techniques for quantification of the target's motions taken as the image information on the video screen is pointed out. Emphasis is put on assuring the data accuracy and the degree of errors on the extracted data from the video photographs recorded by normal video cameras or mobile phones. Furthermore, this approach aims to utilize effectively the various kinds of video resources recorded at the moment of disasters as quantitative data resources to know structural motion of the target structures. As the actual example of the video movies at just the right moment of the disasters, the highrise buildings' free vibrations after the earthquake in 2011 are selected. All the motion videos found for this study are available on the Internet streaming site, and those on-line videos have been uploaded by non-professional photographers who happened to take the video in personal by their mobile phone or handy camera devices. In this paper, investigations for the following items are carried out [1], [2]. Firstly, exactness and resolution on the extracting data from motion pictures recorded by the normal video camera are evaluated. For this aim, the actual video images of the building model specimen on the shaking table tests are used. Through this investigation, the validity of the data extractions by using the normal video camera for sensing displacements is assured. The data property reproduced from the motion videos are investigated and the exactness of the identified motions are evaluated by comparing to the actual measurement data with the displacement sensors equipped directly on the testing specimen. In this study, quantitative results about the data accuracy and the available resolution on the motion captures from the normal video camera are shown. Secondly, the actual video images streamed on the Internet about the free vibrations after earthquakes at the high-rise buildings in Tokyo while the Tohoku earthquake in 2011 are investigated. The data extractions of the displacement on the target building are evaluated. Through this study, as one of the importance for recording scenes, it is considered that the virtual fixed point should be caught on the screen with the target at the same time. It is assured that the probability to success extracting data can be improved, if there is some position to be able to deal with the fixed point on the video images. Furthermore, from the reproducing test supposing to the video recording with the mobile phones, importance of recording the fixed point on the video screen is also investigated and confirmed quantitatively.

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