[Abstract] Based on the view point of strain energy, some problems in structural earthquake analysis have been researched in this paper. Firstly, a general method of judging the adequacy of the number of participation modes is proposed. Secondly, the author advance the concept of “the most disadvantageous earthquake direction” , on which a detailed algorithm is given. Then the direction angle of a mode is defined and the corresponding calculation formulas are also listed. At last, the calculation formulas of the lateral and the torsional vibrating components of a mode is presented.

[Keywords] Ratio of participation energy, The most disadvantageous earthquake direction, Direction angle of a mode, Component of lateral vibration, Component of torsional vibration