A practical 3-dimensional analytical method for earthquake response of steel towers in a power transmission system is described. The method takes into account the differ ence in elevation of conductor support points of adjacent towers, the difference in horizontal angle of lines and the difference in length of spans. Earthquake response analysis using this method was compared with the results of a 500kV conventional 2-dimensional analysis in a horizontal plane. The study also included the effect of the vertical earthquake on the response of the tower, which can not be obtained from the 2-dimensional analysis.
