VIBRATION OF SUSPENSION BRIDGE DUE TO VERTICAL GROUND MOTION

Abstract

As regards the vibration of suspension bridge due to horizontal ground motion, which can be represented by sinusoidal wave, and whose direction is parallel to the bridge axis, the writer has already published the results obtained by model tests and by theoretical analysis at the 2 nd World Conference on Earthquake Engineering, 1960. In order to investigate the vibrational characteristics of vibration of suspension bridged, and to prove the validity of the theory, the writer made a model, whose total length is 548 m, and the vibration tests were done by using the model. After confirming the validity of the theory given by the writer, he applies his analytical method to analyze the vibration of suspension bridges due to vertical ground motion, and performs numerical analysis about the Wakato Bridge, which is now under construction.In this paper, the writer does not analyze the vibrational characteristics of suspension bridges due to horizontal ground motion, whose direction is perpendicular to the bridge axis, because the perpendicular strength of the suspension bridge is mostly checked against large wind load, and usually lateral vibration of the suspension bridge causes the torsional vibration which does not give rise to large additional cable tension.The ratio of vertical acceleration to horizontal one of earthquakes is obtained by using the acceleration records in the past. The number of kinds of cases which are treated in this paper is four, owing to the combination of both side span with stiffening girder or not and condition of the top of the tower, sliding or fixed.