EVALUATION OF THE EFFECTS OF SEISMIC RETROFIT FOR REINFOECED CONCRETE SCHOOL BUILDINGS USING MICROTREMOR OBSERVATION

earthquakes have been occurring frequently in recent years and the importance of seismic retrofit has been pointed out. In this study, the effect of seismic strengthening is investigated by two methods, microtremor observation and a numerical analysis, for retrofitted buildings. Two school buildings were strengthened by different construction methods, one using external braces and another adding a frame. The results of microtremor observation and numerical analysis show that the rigidity of these buildings have improved by implementing seismic strengthening. The microtremor observation shows a higher rate of rigidity improvement than that by the numerical analysis. The factors that are difficult to model, such as non-structural elements and construction accuracy, are taken into consideration in microtremor observation. We must avoid that the natural periods of ground and a building overlap by retrofit. Thus it is important to know change of the natural period of a building by retrofit. We suggest that microtremor observation is a useful tool to confirm the effect of seismic retrofit together with numerical analyses