Abstract
The elastic natural period and the equivalent natural period of railway structures are important indicators in the maintenance and the seismic diagnosis respectively. This paper aims to propose a method for evaluating the equivalent natural period of railway viaducts on the basis of the elastic natural period identified by microtremor measurement. The method for identifying the natural vibration modes with limited measurement points is proposed, in which the characteristics of the vibration mode shapes of viaduct groups are effectively utilized. The method enables to identify the elastic natural period of rigid frame viaducts within a error of 5% approximately. In addition, the ratio of the elastic natural period to the equivalent natural period of rigid frame viaducts is shown to be more or less constant depending on structural type of viaducts. A conversion method based on the ratio can estimate the equivalent natural period within a error of 10% approximately, applied for rigid frame viaducts. However, when the method is applied to piers, errors increase due to the effect of the coupling with the adjacent structures and the ground condition variation.
