This research evaluates local structural conditions of RC columns of viaducts during earthquakes using acceleration measurement data. During strong earthquakes, the stiffness of RC columns reduces more severely during loading time steps than unloading time steps. The stiffness reduction from the unloading time steps to the loading time steps is evaluated as a damage indicator of the columns. A structural parameter identification method is first improved to identify loading and unloading stiffness separately. Then, the method of extracting loading and the unloading time steps are described. The proposed method is applied to a nonlinear SDOF model and a nonlinear viaduct model. Finally, the method is applied to the data sets of a large-scale RC column experiment conducted at E-Defense.
