Development of the Residual Seismic Capacity Evaluation System with Capacity Spectrum Method (2014)

Once a big earthquake occurs, many buildings are severely damaged, and consequently it gives rise to many homeless. The damage level could increase due to an aftershock in some buildings. Thus enormous harm to the inhabitants in such buildings could occur. On the contrary, some people could get caught up in fear and would escape from even the buildings that have enough residual seismic capacity from the engineering point of view. Hence, the number of homeless can increase drastically. In order to reduce further damage due to an aftershock and to reduce the number of homeless, a quick inspection on the damaged buildings must be carried out soon after a main shock. However, under the present situation, the buildings have to be investigated one by one by engineers or researchers. For example, 5,068 engineers and 19 days were needed to investigate 46,000 buildings on a damaged area at the Kobe earthquake. Nineteen days were too long and yet the number of investigated buildings was not enough. Moreover, many buildings were judged as gCaution h level, which needs detailed investigation by engineers. gCaution h judgement is a gray zone and it could not take away anxieties from inhabitants. Furthermore, the current quick investigation system presents a dilemma since buildings should be investigated by visual observation of engineers. Thus, this judgement varies according to the engineers f experiences. After Tohoku Earthquake, it was also found that visual investigation takes too long time for high-rise buildings. Most of them were designed so that building forms weak beam strong column mechanism. That makes visual investigation difficult, since beams are usually covered by ceiling system. In order to solve the problems mentioned above, authors have been developing the real-time residual seismic capacity evaluation system, which needs only few relatively inexpensive accelerometers. The system calculates the performance and demand curve from a measured acceleration of the basement and of each point of a structure with inexpensive accelerometers, and further estimate the residual seismic capacity of a structure by comparing these curves. To draw the performance curve, the absolute response accelerations and relative response displacement at each point are needed. Response displacements are derived from measured accelerations by double integral. It is well-known that the error components contained in the measured acceleration grows much by double integral. Therefore, the Wavelet Transform Method (WTM), which is a powerful time-frequency analysis method, is applied. The WTM is a method that decomposes a signal in temporal domain with holding the best relationship between the time increment and frequency increment for the decomposition. The error component that has relatively long period can be decomposed and eliminated by using the WTM. In this paper, the health monitoring results of the building for the department of architecture, Yokohama National University, one span one bay single story R/C specimen for a shaking table test, and full scale one span one bay three story R/C frame specimen for a shaking table test will be presented and the validity of the proposed structural health monitoring method will be discussed.