Abstract
We present a simple method to estimate the horizontal incident direction of earthquake ground motion, which gives most severe response of a curved girder bridges: we call it “critical direction.” To find the critical direction, most of designers have to calculate dynamic responses of a structure for incident waves from various azimuth. Thus, the many resources are required for calculation. To diminish such the difficulty in numerical calculation, we improve a method proposed by Okano. He has developed a method to estimate the principal axis of the ground using coherence functions among the observed time traces of earthquake ground motion. It is concluded that the proposed method can reduce the cost for numerical calculation without a lack of accuracy.
